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Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
Human resources section_8-textbook_on_public_health_and_community_medicine
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  • 1. 10095752550
  • 2. Section 8 : Entomology in Public Health Practice154 Introduction to Entomology Rina Tilak 903155 Principles of Vector Control Rina Tilak 906156 Housefly Rina Tilak 927157 Mosquitoes Rina Tilak 931158 Fleas Rina Tilak 940159 Human Lice Rina Tilak 944160 Sand Flies Rina Tilak 946161 Some Annoying Pests Rina Tilak 948162 Envenomizing Pests Rina Tilak 952163 Ticks and Mites Rina Tilak 955164 Rodents Rina Tilak 960166 Snakes Rina Tilak 966
  • 3. (iv) Order Hemiptera : It contains the bedbugs and some other 154 Introduction to Entomology species like kissing or ‘assassin’ bugs, which act as vectors of ‘Chagas’ disease. Rina Tilak (b) Class Arachnida : It includes arthropods like ticks, mites, spiders and scorpions. The class is characterized by the presence of eight legs, body divided into two parts viz. cephalothoraxThe word ‘Entomology’ is derived from the Greek words (head and thorax are fused together) and abdomen and‘ENTOMON’ meaning an insect and ‘LOGOS’ meaning science, absence of antennae and wings. The cephalothorax bears sixthus ideally making Entomology ‘the branch of science which pairs of appendages, the first two pairs function as mouthpartsdeals with the study of insects’; however, the scope of the (chelicerae and pedipalps) and last four pairs as walking legs.subject has been broadened to include study of all Arthropods.Phylum Arthropoda constitutes all invertebrates with jointed (c) Class Crustacea : It includes lobsters, crabs, water fleasappendages and presence of chitinous exoskeleton besides and cyclops; some species of these are intermediate hosts ofother features. The word Arthropoda is derived from two words certain human helminths, e.g. Cyclops as intermediate host of‘ARTHRON’ meaning jointed and ‘PODA which means legs or ’, guinea worm infestation.appendages. The Phylum has many important classes of which (d) Class Myriapoda : It includes centipedes and millipedes.Class Insecta is the largest, constituting more than four million Modes of Disease Transmissioninsect species. The other important classes are Arachnida,Crustacea and Myriapoda. Arthropods transmit diseases to man through specialized modes of disease transmission. The modes of disease transmission byVector borne diseases are one of the leading causes of morbidity arthropods can be classified as under :and mortality the world over and pose a major public healthchallenge especially to the third world or developing countries. Direct Contact : When two hosts are in direct contact withOne of the important measures to combat these diseases is other, the arthropod vector itself gets transferred from one hostthrough control of vectors. To ensure effective vector control, to the other, e.g. pediculosis and scabies.the knowledge about their lifecycle, habits, habitat and Mechanical transmission : In this mode of transmission,diseases transmitted is essential. The chapters in this section the disease causing organism is transmitted on the outsidewill guide the reader on these aspects so that sound vector or inside the bodies of arthropods without undergoing anycontrol strategies can be formulated, wherever and whenever, development, propagation or any changes in the pathogenicityvector control is desired. e.g. diseases transmitted by houseflies - diarrhoea, dysentery,Classification of Arthropods cholera, hepatitis A & E etc.Diversity of structures amongst arthropods necessitates the Biological Transmission : The disease causing organismsub-division of the phylum Arthropoda into a number of undergoes certain biological changes inside the body of theclasses, orders, families, genera and species. The following vector. Depending on the type of biological changes, biologicalclasses include species of medical importance. transmission has been further classified as :(a) Class Insecta : It comprises about 70% of all the known Cyclo-developmental : In this mode of transmission, thespecies in the animal kingdom. The insects are characterized disease causing organism undergoes a part of its cycle in theby the presence of six legs, body divided into head, thorax and vector and simply develops or grows inside the body of theabdomen and presence of antennae besides other features. vector, e.g. Wuchereria bancrofti (Filariasis) transmitted byThe head bears the mouthparts, eyes in the form of compound Culex female.or simple eyes or at times may have no eyes and a pair of Cyclo-developmental-propagative or Cyclo-propagative :antennae. The thorax is subdivided into three segments with a In this mode of transmission, the disease causing organismpair of legs in each called the pro, meso and metathoracic legs. undergoes a part of its life cycle in the vector and also grows/The class is further subdivided into 29 orders of which only 4 develops and multiplies inside the body of the vector. Examplecontain species of medical importance. is Plasmodium sp (Malaria) transmitted by Anopheles female.(i) Order Diptera : It possesses one pair of wings and a pair Propagative : In this transmission mode, the disease organismof ‘halters’, which are vestigial wings. This is the largest order simply grows and multiplies in the body of the vector, e.g.comprising about seventy thousand described species with Yersinia pestis (Plague) transmitted by rat flea and allworld wide distribution. It contains such insects of medical bacterial, viral, spirochaetal or rickettsial diseases transmittedimportance as mosquitoes, sandflies, simulium flies and by arthropods.house-flies. Other Specialized Modes of Disease Transmission : These(ii) Order Anoplura : It comprises true or sucking lice, which specialized modes of disease transmission are generallyare parasitic on mammals and the chewing lice, which infest encountered in ticks and mites.birds as well as mammals. Lice of medical importance to man Trans-ovarian : The disease organism is transmitted to eggsare human lice. through ovary of infected female, e.g. Orientia tsutsugamushi,(iii) Order Siphonaptera : It contains many species of fleas the agent for Scrub typhus transmitted by trombiculid mite-including the rat flea, which is a vector of plague and endemic Leptotrombidium deliense.typhus. • 903 •
  • 4. Table - 1 : Important arthropod borne diseases Disease Vector Causal organism Reservoir I Mosquito borne diseasesMalaria Anopheles species Plasmodium species ManFilariasis Culex quinquefasciatus W bancrofti (nocturnal, periodic) Man Aedes niveus group W. bancrofti (diurnal sub-periodic) Man Mansonoides species Brugia malayi Man, PrimateChikungunya Aedes species Arbovirus group A ManDengue fever & DHF Aedes species Arbovirus group B ManYellow fever Aedes species Arbovirus group B Man/ MonkeysJapanese Encephalitis Culex vishnui group Arbovirus group B Mammals/ Birds (C tritaeniorhynchus) II Sandfly borne diseasesLeishmaniasisVisceral (Kala azar) Phlebotomus argentipes Leishmania donovani Man/MammalsCutaneous (Oriental sore) P. papatasi L. tropica Man/MammalsEspundia P. sergenti L. braziliensis Man/MammalsSandfly fever P. sergenti, P. papatasi Virus Man III Fly borne diseasesBacillary dysentery M domestica Shigella ManAmoebic dysentery M domestica E. histolytica ManGastroenteritis M domestica Specific/Non specific organisms Man/animalsTyphoid M domestica Salmonella typhi ManParatyphoid M domestica Paratyphoid A&B ManCholera M domestica Vibrio cholera ManPoliomyelitis M domestica Virus ManViral hepatitis (Type A) M domestica HAV ManTrachoma M domestica C trachomatis ManYaws M domestica T pertenue Man IV Flea borne diseasesPlague (Bubonic) Xenopsylla species Yersinia pestis RodentsEndemic/Murine Typhus Xenopsylla species R. typhi Rodents/ Domestic animalChiggerosis (Jigger) - - Tunga penetrans (chigoe) Dogs, cats, wildDipylidium caninum Ctenocephalides. felis/canis Dipylidium caninumHymenolepis diminuta Hymenolepis diminuta Carnivores X cheopis / N fasciatusH nana X cheopis / C canis/ Pulex irritans H nana Rats, mice V Louse borne diseasesEpidemic typhus Pediculus humanus R. prowazeki ManEpidemic relapsing fever Pediculus humanus Borrelia recurrentis ManTrench fever Pediculus humanus Bartonella quintana Man/animalsDermatitis Pediculus humanus/ capitis Secondary organisms Man VI Tick borne diseasesKyasanur Forest Disease (KFD) Hard ticks species Arbovirus group B Monkeys/BirdsTick typhus Hard ticks species R conorii DogsTularaemia Hard ticks species P tularensis Rabbits/ Rodents/ cattleRelapsing fever Soft Tick B duttoni Rats VII Mite borne diseasesScrub typhus L. deliense Orientia tsutsugamushi RodentsRickettsial pox Allodermanyssus sanguineus1 R akari RodentsScabies S scabei - Man VIII Cyclops transmitted diseasesDracontiasis Cyclops species D medinensis ManFish tape worm Cyclops species D. latum Fish IX Reduviid bugsChagas disease Reduviid/Cone-nosed T cruzi Domestic animals/ man X Tsetse fliesTrypanosomiasis Glossina species T gambiense and T rhodesiense Wild animals/ cattle/ man • 904 •
  • 5. Trans-stadial : The disease causing organism is transmitted Study Exercisesfrom one stage to another e.g. Tick typhus organism - Rickettsia Short Notes : Modes of disease transmission.conorii transmitted from infected larva to nymph to adult. MCQs & ExercisesArthropod Borne Diseases 1) Class Insecta is characterised by presence of how manyArthropods are responsible for transmission of innumerable legs? : (a) 4 (b) 5 (c) 6 (d) 8diseases. Some of the important arthropod borne diseases is 2) Mosquito belongs to the order a) Diptera (b) Anopluralisted in Table - 1 along with their vectors, causative organisms (c) Siphonoptera (d) Hemiptera.and reservoir hosts. 3) Mode of transmission of malaria by Anopheles is : (a) Cyclo - developmental (b) Cyclo - propogativeSummary (c) Propagative (d) Cyclo - developmental propagativeEntomology is the branch of science which deals with the 4) Orientia tsugtsugamushi is the causal organism for thestudy of insects, however, the scope of the subject has been diseases (a) Scrub typhus (b) Epidemic typhus (c) Endemicbroadened to include the study of all Arthropods. Amongst typhus (d) Tick typhus.the many important classes of the phylum, Insecta is the 5) Which of the following is not a mosquito borne disease :largest constituting more than 4 million species. Vector borne (a) Dengue (b) Filaria (c) Leishmaniasis (d) Yellow feverdiseases are one of the leading causes of morbidity & mortality 6) Aedes species cannot transmit : (a) Chickungunyaespecially in the developing countries. These diseases can (b) Dengue haemorrhagic fever (c) Japanese Encephalitisbe largely combated by effective vector control for which a (d) Yellow feversound knowledge of the bionomics of the vector is needed. The 7) Causal organism for bubonic plague : (a) R typhiimportant classes of Phylum Arthropoda are Insecta, Arachnida, (b) Y pestis (c) H nana (d) H diminutaCrustacea, Myriapoda. The class Insecta is characterized by 8) Murine Typhus is transmitted by : (a) Hard tick speciespresence of six legs, body divided into head, thorax & abdomen. (b) Soft tick species (c) Xenopsylla species (d) TrombiculidThe class has 4 orders of medical importance, Diptera, Anoplura, Mite speciesSiphonaptera & Hemiptera. The order Diptera has 1 pair of 9) Causal organism for epidemic Typhus : (a) B quintanawings and contains insects such as mosquitoes, sandflies, (b) R prowazeki (c) Borrelia recurrentis (d) R typhisimulium flies and houseflies. The order Anoplura comprises 10) KFD is transmitted by : (a) Soft Tick (b) Mite (c) Hard Ticktrue or sucking lice. Order siphonoptera includes the rat flea; (d) Licethe order hemiptera contains bed bugs. The class Arachnida 11) ___________ is the largest class of Phylum Arthropodaincludes ticks, mites, spiders and scorpions; body is divided constituting more than __________ insect speciesinto cephalothorax and abdomen and presence of eight legs. 12) Direct mode of transmission is seen in _______ & ______The class crustacea includes lobsters, crabs, water fleas and 13) Entomology is derived from the Greek word ENTOMONCyclops. Myriapoda includes millipedes and centipedes. meaning _________ & LOGOS meaning __________Arthropods transmit diseases to man by different modes of 14) Arthropoda is derived from two words ARTHRON meaningtransmission, mainly direct, mechanical & biological. In direct __________ & PODA meaning __________transmission, two hosts come in direct contact with each other 15) Leptotrombidium deliense is vector for __________e.g. pediculosis & scabies, mechanical transmission where Answers : (1) c; (2) a; (3) b; (4) a; (5) c; (6) c; (7) b; (8) c;disease causing organism is transmitted without undergoing (9) b; (10) c; (11) Insecta ; 4 Million; (12) Pediculosis;any change in pathogenecity or development e.g. diseases Scabies; (13) Insect, Science; (14) Jointed, Appendages;transmitted by houseflies. Biological transmission is further (15) Scrub Typhus.divided into cyclodevelopmental - the disease causing organismundergoes part of its life cycle in the vector e.g. Wuchereria Further Suggested Readingbancrofti; cyclopropogative - the disease causing agent 1. Gordon C cook, Alimuddin Zumla, Manson’s Tropical diseases, 21st Ed, 2003, Chapter 50, Rickettsial infections, p 900.undergoes part of the lifecycle in the vector & also multiplies 2. Service Mike. Medical Entomology for students. 3rd ed. Cambridge :inside the vector e.g. malaria transmitted by Anopheles female. Cambridge University Press, 2004.The other mode is propogative where disease causing organism 3. Kettle DS. Medical and Veterinary Entomology. 2nd ed. CAB International, 1995.simply grows & multiplies in the body of vector e.g. Yersinia 4. Hati AK. Medical Entomology. Allied Book Agency, Kolkata, 2001.pestis (plague) transmitted by rat flea, other specialized modesare transstadial & transovarian. • 905 •
  • 6. stream flushing and regulation of the water level in reservoirs, 155 Principles of Vector Control vegetation removal, shading and exposure to sunlight. (c) Modification or Manipulation of Human Habitation or Rina Tilak Behaviour : This means “A form of environmental management that reduces man-vector - pathogen contact”. Examples of this approach are siting of settlements away from vector sources,Control of arthropods is one of the key strategies in the mosquito/rodent proofing, personal protection and hygienicmanagement of vector borne diseases. A strategist should measures against vectors and provision of mechanical barriers,have sound knowledge of the bionomics, distribution, seasonal providing facilities for water supply, disposal of waste waterprevalence, vectorial capacity, insecticide susceptibility status and excreta, laundry, bathing and recreation to prevent orand role of arthropods in diseases transmission coupled with discourage human contact with infested water.the knowledge of identification features of the incriminatedvectors for formulating effective control strategies. Once armed Chemical Controlwith this knowledge, the choice of effective vector management The new era of control of vector borne disease began with thetools may be exercised; the range and sophistication of control discovery of the insecticidal value of Dichloro Diphenyl Trichloromethods is impressive. The various control options available ethane (DDT). DDT was first synthesized by Othmar Zeidler inare as follows : 1874 at Strasbourg, Germany. In 1939, Paul Muller of the Geigy●● Environmental Control Company in Basle, Switzerland, discovered its remarkably long●● Chemical Control residual insecticidal property, earning him the Nobel Prize in●● Biological Control Medicine. The availability of several effective, safe and low●● Personal Protective measures cost pesticides, coupled with improvements in the techniques●● Mechanical control of their application, made it possible for many governments in●● Physical control the developed as well as developing countries to embark upon●● Genetic control extensive countrywide programmes for the control or eradication●● Legislative control of vector borne diseases. However, development of resistanceEnvironmental Control amongst vectors to insecticides has necessitated reassessment of the place of pesticides in vector control programmes. BesidesThe important environmental control measures which are the technical and financial difficulties, there is a growingincreasingly being used are described below : concern about the environmental contamination resulting fromEnvironmental Management the persistent use of insecticides.This has been defined as “The planning, organization, carrying Classification of Insecticidesout and monitoring of activities for the modification and/or Pesticides may be classified in many ways based on mode ofmanipulation of environmental factors or their interaction with entry, target stage, chemical composition and mode of action.man with a view to prevent or minimize vector propagation and However, the most common classification used is based onreducing man-vector-pathogen contact.” This is a naturalistic chemical composition. According to this classification, theapproach which attempts to extend and intensify natural insecticides are classified in the following categories asfactors which limit vector breeding, survival and contact with presented in Fig. - 1.man.(a) Environmental Modification : It is defined as “A formof environmental management consisting of any physicaltransformation that is permanent or long-lasting of land, water and vegetationaimed at preventing, eliminating or Fig. - 1 : Classification of insecticides as per chemical compositionreducing the habitats of vectors without Insecticidescausing unduly adverse effects on thequality of the human environment”. Natural SyntheticEnvironmental modification includesdrainage, filling, velocity alteration, Plant Based Inorganic Organicland levelling and transformation of Pyrethrum Mineral Oils Paris Greenimpoundment margins. Azadirachtin(b) Environmental Manipulation : Itis defined as “A form of environmental Organophosphates Syntheticmanagement consisting of any planned Malathion Pyrethroids Carbamatesrecurrent activity aimed at producing Temephos Deltamethrin Organochlorines Propoxurtemporary conditions unfavourable to Fenthion Cyfluthrin DDT Bendiocarbthe breeding of vectors in their habitats”. Dichlorvos Bifenthrin CarbarylExamples of environmental manipulation Fenitrothion Lambda-Cyhalothrinactivities are water salinity changes, Pirimiphos methyl Permethrin • 906 •
  • 7. Natural Insecticides Chapter on Mosquitoes for further details on use). As per Govt.Plant based of India Gazette notification number S.O. 378(E) dt 26th May 1989, the use of DDT in Agriculture has been withdrawn andPyrethrum : Pyrethrum extract is obtained from the dried restricted to 10000 MT/ annum for Public Health programmeheads of the flower Chrysanthemum cinerariafolium and except in case of North East as Insecticidal Residual Spraycontains the active ingredients pyrethrins I and II, constituting (IRS).1 to 2% of the total weight of the raw pyrethrum. Pyrethrum ischaracterized by rapid knockdown action on arthropods even Organophosphorus Compounds : These insecticides arewhen used in very low dilution. It is very unstable in light and derivatives of phosphoric acid and act by inhibiting theair and has practically no residual effect. This makes repeated activity of cholinesterase. Many of the insects, which haveapplications necessary. Pyrethrum is available as 2% extract, become resistant to Organochlorines are still susceptible towhich needs 20 times dilution to make it 0.1% solution, which the members of this group. However, due to their extensiveis actually used for spraying. Using a 0.4 mm or lower calibre use in agricultural as well as public health field, more andnozzle, 50 to 100 ml of pyrethrum solution in kerosene oil is more insects are developing resistance to Organophosphorussprayed per 100 m3 of space. Addition of an Organophosphorus compounds. Some of the common compounds are Malathion,insecticide to pyrethrum formulation is a common commercial Temephos, Fenthion, Dichlorovos (DDVP) and Fenitrothion.practice for obtaining a better effect. It is one of the main Malathion : It is one of the least toxic Organophosphorusinsecticidal constituents in aerosol dispensers and also an compounds. Malathion is a broad spectrum insecticide, withinsecticide of choice for ULV sprays. Pyrethrum is perhaps the efficacy against a large number of pests ranging from mosquitoes,most acceptable insecticide for use in cook houses, dining halls houseflies, cockroaches, bedbugs, lice etc. It is available asand other food preparation areas. Malathion Technical (95%) for use as space spray, 50% WaterAzadirachtin : The active ingredient Azadirachtin is obtained Dispersible Powder (WDP) and Emulsifiable Concentrate (EC)from the seed kernels of neem plant Azadirachta indica. for residual control and 90% dust for use against fleas and lice.Azadirachtin has insecticidal, fungicidal, bactericidal, viricidal Malathion under the National Vector Borne Diseases Controlproperties including insect growth regulating qualities besides Programme of India is being used as Indoor Residual Spraydeterrent, anti-ovipositional, anti-feedant, fecundity and against mosquitoes in areas where the vectors have becomefitness-reducing properties on insects. It has been variously resistant to DDT. The dosage of its application is 2 g/m2 (Referformulated for mosquito larval and adult control in the form to Chapter on Mosquitoes for further details). As ULV spray itof liquid and cream formulations. Neem products contain up has been very widely used during outbreaks of Dengue and JEto 3% Azadiractin. as an anti adult mosquito measure. However, development of resistance has been reported in a large number of vectors toMineral Oils : Kerosene oil, diesel oil, petrol and crude engine Malathion.oil have been successfully used as mosquito larvicides. Theoil film cuts off the air supply, enters and blocks the trachea, Temephos : It is available as 50% EC. It is the only insecticidemay act as a stomach poison, and also lowers surface tension approved for use in potable water. Because of its low toxicity,which prevents larvae from floating. Malariol is the best and it has been successfully used for the control of Anopheleseasiest larvicidal oil to use for Anopheline and Culicine larvae. stephensi breeding in wells and domestic containers at aMalariol is used as it is @ 10 litres per 500 linear meters. dosage of 1ppm (Refer to Chapter on Mosquitoes for details). Sand impregnated with Temephos in 1% concentration has beenSynthetic Insecticides : These can be organic or inorganic. used in some countries against Aedes aegypti which breeds inThe only inorganic compound used in vector control (mosquito containers of clean and potable water. It has proved to be verylarvicide) was Paris green (Copper-aceto-arsenite). It acted as successful in Guinea worm eradication programme in India.stomach poison when ingested by mosquito larvae. However, itis not used any more for mosquito control. Fenthion : It is formulated as 82.5% EC and as granules containing 2% toxicant. It is a good mosquito larvicide but canThe Organic Insecticides fall into four major groups viz. not be used in potable water bodies. It is highly effective as aOrganochlorines, Organophosphates, Carbamates and Synthetic larvicide against Culex quinquefasciatus or any other vectorpyrethroids. found breeding in non potable water bodies at a dosage of 1Organochlorine Compounds : These compounds are contact ppm (Refer to Chapter on Mosquitoes for further details). Itpoisons and act on the nervous system. These or their can also be used for housefly control as a larvicide (Refer todegradation products are more or less stored in body fat and Chapter on Houseflies for details).may be demonstrated in milk, urine or sweat. They all have Pirimiphos methyl : This insecticide is being considered as anvariable residual action for variable periods and are toxic to alternative insecticide for Indoor residual spray. It is availableman and animals. The most important and the only member of as 25% WP; 2 kg is mixed in 10 litres of water and sprayed @ 10this group used in Public Health is DDT. litres/ 250 sq m area to give a deposit of 2g/sqm. Three roundsDichloro-diphenyl-trichloroethane (DDT) : Currently DDT is of spray are recommended as is followed in case of Malathion.being used for indoor residual spray in the North Eastern states Dichloro-dimethyl-dichlorvinyl-phosphate (DDVP orof India. A deposit of 1 g of DDT/m2 of surface area of walls Dichlorvos) : It differs from other organophosphorusand ceiling upto a height of 3.5 m in all dwellings applied at 8 compounds in that it possesses a much greater vapour pressureweeks’ interval, effectively controls majority of the mosquitoes at ordinary temperature which produces fatal insecticidaland also other arthropods resting on the treated wall (Refer to • 907 •
  • 8. vapour. It is available as 72.6% EC. It can be combined with solid are available as Pretreated or Long Lasting Nets (LLNs).substances like wax and used as tablets or bricks thus allowing Other Synthetic pyrethroids used in Public health : Thereit to evaporate slowly. It is one of the common insecticides used is a large range of molecules used in the field of Public healthfor disinsecting aircraft. It is an effective housefly larvicide. besides the ones listed above. These molecules are Allethrin,Fenitrothion : It is available as Fenitrothion 40% water Resmethrin, Phenothrin, Cypermethrin, Imiprothrin, Bifenthrin,dispersible powder (WDP). The insecticide has shown promise Cyhalothrin, Cyphenothrin etc. These are all available as WP EC ,as an effective insecticide for control of bedbugs; however or Aerosol formulations for use against pests like cockroaches,toxicity constraints have limited its widespread use. houseflies and mosquitoes.Carbamates : These compounds are derivatives of carbamic Newer Group of Insecticidesacid and resemble Organophosphorus compounds in their Phenyl pyrazoles : Fipronil is the only member of this class ofmode of action. Some of the preparations produce a rapid insecticide. Fipronil acts by antagonizing the effect of GABA.knockdown effect like that of pyrethrum. The inhibition of It is available as 0.3% Gel for use against cockroach as a crackAcetylcholine esterase is reversible with Carbamates and hence and crevice treatment. It is a systemic material with contactthese compounds are less toxic. Some of the compounds in and stomach activity. It has a unique action called ‘cascadecommon use are Propoxur, Carbaryl and Bendiocarb. effect’ which is evident due to necrophagy seen in cockroaches.Propoxur : It is formulated as WDP as well as EC. It is considered When cockroaches consume the insecticide bait, they are killed;as the least toxic Carbamate compound for man and domestic these dead cockroaches when consumed by other cockroachesanimals. It has a flushing out effect and therefore is commonly bring about the death of these cockroaches and this goes on forused for cockroach and bedbug control. It is also used in bait about two months or so, thus obviating the need to retreat theformulations against houseflies and cockroaches. area at lesser intervals.Bendiocarb : Bendiocarb is an alternative insecticide for Indoor Neo Nicotinoids : Imidacloprid is the sole member from thisresidual Spraying. It is available as 80% WP For indoor residual . class. It acts by causing irreversible blockage of postsynapticspraying, it is recommended @ 200 mg/sqm. Two rounds of acetylcholine receptors. Imidacloprid is a systemic insecticide,spray are recommended for effective control against malaria. having notable contact and stomach action. Imidacloprid isSynthetic Pyrethroids : These are synthetic derivatives or available as 2.15% Gel for use against cockroaches and as Baitanalogues of natural Pyrethrum. These are broad spectrum, for use against houseflies, where it is formulated with houseflyhighly potent with quick knock down action and long residual pheromone - Muscalure.life. Synthetic pyrethroids are many times more effective than Biorational Insecticides : ‘Biorational’ means any substancethe previously available insecticides. Their relative safety of natural origin that has a detrimental or lethal effect onto man and higher animals, their efficient biodegradability specific target pest, e.g. insects. These insecticides are non-together with their higher target specific toxicity makes toxic to man, plants and animals and have little or no adversethem very attractive materials for integrated vector control. effects on the environment. An overview of the biorationalThe commonly available products are Permethrin, Allethrin, insecticides is presented in Fig. - 2.Phenothrin, Cypermethrin, Cyfluthrin, Deltamethrin andBifenthrin. The Synthetic pyrethroids are formulated as WDP , Fig. - 2 : Biorational Insecticides Used in Vector ControlEC, SC, Flow, EW and ULV formulations. Being broad spectrum,these insecticides are being used for vector control as residual Biorational Insecticidesspray, space spray and topical application as well as fortreatment of clothing. Pheromones BiocidesDeltamethrin : It is one of the most widely used Synthetic Insect Growthpyrethroid molecule in the field of vector control. It is available  Muscalure  Bacillus Regulatorsin many formulations for various vector control strategies viz.  Oviposition attractant thuringiensisSC 2.5% (Flow) formulation for treatment of bednet and routine var israelensishousehold pest control activity; 2.5% WP formulation for Indoor  BacillusResidual spray in Malathion resistant areas and 1.25 ULV for sphaericusspace spraying. The target dose (for Indoor Residual Spray) is Chitin Synthesis Juvenile Hormonegenerally 20 mg of a.i. (active ingredient) per sq m of surface Inhibitors Mimicsarea.  Diflubenzuron  Methoprene  Lufenuron  PyriproxyfenCyfluthrin : Besides Deltamethrin, this is the next most widely  Novaluron  Fenoxycarbused molecule. It is available as 0.5% EW formulation for  Triflumurontreatment of bednets; 5% EC for household use and 10% WP foruse as indoor residual spray in Malathion resistant areas.Permethrin : Widely used for control of lice, scabies and for Insect Growth Regulators : A new approach to vector controltreatment of clothing and bednets. The product is formulated in is the use of substances that adversely affect insect growthvarying concentration as Shampoo formulation for use as anti- and development. The enzymes and hormones that regulatelice treatment and 5% cream for use in scabies treatment. Bed developmental processes within an insect’s body can sometimesnets treated with Permethrin at the manufacturing stage itself be exploited as chemical control weapons. These compounds, • 908 •
  • 9. often known as Insect Growth Regulators (IGRs) can be used houseflies) and oviposition attractant (Aedes control) haveto stimulate development at inappropriate times or inhibit it been exploited in the field of vector management.at other times. They are quite selective in their mode of action Biocides : The development of insecticide resistance amongstand potentially act only on target species. Most of the IGRs that the major pests and vectors coupled with the non target toxicity,have shown effectiveness against insect pests, cause the rapid necessitated development of safer alternatives to insecticides.death of the insect through failure of a key regulatory process This led to the screening, promotion and use of a large numberto operate or function. IGRs generally control insects either of biorational products of which biocides are one of the mostthrough inhibition of chitin synthesis or interference with important control options. The two biocides used in the fieldmetamorphosis by mimicking the action of juvenile hormone. of vector control are Bacillus thuringiensis var israelensis andThe major groups of IGR compounds include : Bacillus sphaericus. Both these products are widely used asChitin Synthesis Inhibitors : These chemicals inhibit the larvicides in Mosquito control programmes and act as stomachmoulting process by blocking the activity of chitin synthetase, poison.an enzyme needed by epidermal cells when constructing Bacillus thuringiensis var israelensis (Bti) : It was discovereda new exoskeleton. Because of this mode of action, Chitin in 1976 and has been found to be effective as mosquito larvicide.Synthesis Inhibitors (CSIs) are highly specific to arthropods. It is a gram positive spore forming bacteria. Bti produces toxinsThey act rather slowly (2-5 days), but eventually disrupt any which are present in parasporal body called the ‘protein crystal’.process that involves construction of new cuticle (e.g., molting, It primarily kills by the action of delta-endotoxin. When thehatching, pupation). They are most effective when used against mosquito larva ingests the protein crystal (inactive protoxin),the immature stages of a vector. Diflubenzuron, is used for it is activated inside its midgut by the action of proteases intocontrolling mosquitoes, houseflies etc. It is available as 25% active protoxin; these bind to the cell receptors present onEC, WP & 0.5% Granules and is used @ 1.0 g/ acre of surface midgut epithelium and cause disturbance in osmoregulatorywater as mosquito larvicide. Lufenuron, is a systemic CSI and mechanism which leads to swelling and eventual bursting ofis especially effective for flea and tick infestation control on the epithelium and finally death of the larvae. The product isanimals. Novaluron is a recent addition to the list, which has available as WP Granules, AS & Briquette. Bti 12 AS is used @ ,been found effective against the mosquitoes. It is a contact 20ml/m2 and has been found to be effective up to 15 days (forlarvicide and is available as 10% EC. It is used @ 20 μg a.i./ l details refer chapter on mosquito). Bti however, suffers fromand the efficacy lasts up to 3 months. the disadvantage that it can not be used in polluted watersJuvenile Hormone Analogues or Mimics : Juvenile hormone or where particulate matter is more; it also cannot recycle inanalogues or Juvenile Hormone Mimics (JHM’s) act by inhibiting nature. It is used in non potable water bodies.the developmental changes associated with embryogenesis, Bacillus sphaericus : A naturally occurring bacterium usedmorphogenesis, and reproduction. During normal development, against mosquito larvae. It is more effective in polluted waterJH levels are elevated in larvae (or nymphs) and decrease and can recycle and persist in nature. It is available in variousprior to pupation (or adult eclosion). Contact exposure to JH formulations like Bti viz. pellets, briquettes, granules & WP It .analogues during the egg stage or after the last larval molt is used @ 20ml/m2 and has been found to be effective up tocan inhibit development, delay maturation, and eventually three weeks.result in death. Since the onset of mortality is usually quite Fumigants : Some of the fumigants used as pesticides areslow (days to weeks), these chemicals are not used during carbon tetrachloride, methyl bromide, ethylene dibromide,epidemics; however, these chemicals are much in demand for chloropicrin, carbon disulphide and dichlorvos (DDVP).routine vector control due to their specificity and safety tonon-target organisms. Several compounds (e.g., Methoprene, Application TechniquesPyriproxyfen, Fenoxycarb, Triflumuron) have been successfully Control of arthropods in different habitats necessitates the useincorporated into vector management programmes especially of different types of spraying equipment as well as a variety ofDengue and Malaria and in products used for controlling ants, formulations such as liquids, granules and dusts. For examplefleas, and other household pests. Pyriproxyfen can cause control may involve treatment of small domestic or peridomesticsterilization and inhibition of growth of adult insects; it has a water collections which are ideal breeding places for Aedesresidual effect up to 3 to 6 month indoors and 30 days outdoors. mosquitoes; applications to stagnant waters in cesspools,It is widely used against mosquitoes @ 2gm a.i./ sq m. ditches and drains where Culex mosquitoes breed, large bodiesPheromones : Pheromones are semiochemicals (chemicals of standing water where certain Anopheles mosquito specieswhich mediate interactions between organisms) secreted by may be breeding; or aerosol spraying of extensive areas to haltan organism which provokes specific reaction in receiving epidemics. To meet with diverse situations, significant progressorganisms of the same species. These chemicals may further has been made in improving the spraying equipment. The Ultrabe classified based on the type of interaction mediated e.g. sex Low Volume (ULV) equipment for ground and aerial spray topheromone (muscalure secreted by houseflies), oviposition control mosquitoes and other haematophagous arthropods hasattractant (mosquito larvae), aggregation pheromone resulted in not only the elimination of several impediments(cockroach, bedbugs), alarm pheromones, trail pheromones like frequent mixing and reloading but helped in increasingetc. The scope of pheromones in vector control is promising, the speed of application and reducing the dosages and costs. Ithowever so far only two pheromones viz. Muscalure (in is specially recommended for control of an outbreak of vectorcombination with Imidacloprid insecticide as baits against borne disease. • 909 •
  • 10. Formulations from 1 to 5%. These can be used in irrigation channels, irrigated or flooded lands, paddy fields and particularly whereManufacturers combine pesticides with other materials there is vegetation on the water surface. After sinking, theseto make usable concentrations called formulations. These formulations disintegrate slowly releasing small particles offormulations are designed to kill insects readily without insecticides. These can be effectively used also in small watercausing undue hazards to non-target organisms when diluted collections such as ornamental tanks and earthen pots, treeand applied correctly. Factors influencing application and holes and other domestic or peridomestic breeding places ofefficacy of an insecticide are its toxicity, size and shape of Aedes mosquitoes.its particles, concentration in formulation; type of solventused, type of surface to be sprayed, atmospheric temperature Wettable Powder : This formulation consists of the technicaland humidity, type of sprayer and its nozzle, training of the grade pesticide, an inert carrier and a wetting agent (usually aspraying personnel, the bionomics, morphology and physiology synthetic detergent) that helps it mix with water. These usuallyof the particular arthropod. No single preparation can meet the contain 50 to 75% of the toxicant. Most of these can be putrequirement of vector control in all spheres of human ecology. directly into water and require only slight agitation to makeSolutions, emulsions, suspensions, water dispersible powders, suspension; others may require mixing with a small amount ofdusts and granules to suit different conditions and problems water to form a paste or slurry. The required volume of waterare therefore, prepared and used. is then added to paste or slurry followed by thorough agitation of the mixture.Technical Grade Pesticide When water is added to a wettable powder it makes a suspension;This is the basic toxic agent in its purest commercial form. this enables the pesticide to stay on porous surfaces likeSome technical grade pesticides are liquids; others occur in concrete, plaster or unpainted wood. Water penetrates thesesolid form. Technical grade Malathion is used in ultra low surfaces, leaving the carrier and the maximum amount of thevolume space applications. pesticide on the surface available to kill pests. Suspensions haveTypes of Formulations other advantages, too. They have no solvent odour, and theyFormulations essentially are of three types : Solid or dry, liquid don’t tend to irritate or penetrate skin. However, they generallyand gaseous formulations. need agitation to keep pesticidal particles from settling out.Solid or Dry formulations Also, they tend to clog sprayer nozzles and strainers, especially when the wettable powder is stored for long periods in humidDusts : Dusts are normally ready-to-use formulations with a areas or when a high concentration is used.low percentage of active ingredient (usually 1 - 10%) plus a Liquid formulationsvery fine inert carrier such as talc, chalk, diatomaceous earth,clay or volcanic ash. These materials are usually low in cost, Emulsifiable Concentrates : Emulsifiable concentrates consisteasy to apply, non-staining and non-toxic to vegetation. Dusts of the technical grade pesticide (typically 45% to 75%), a solvent,are always used dry and can easily drift into non-target areas and an emulsifying agent, usually a synthetic detergent. Thisif they are not applied carefully. For this reason, outdoor agent is used to allow the concentrate to be diluted in water,applications should be made only when the wind is calm. A resulting in an emulsion.common use for dusts is in crack and crevice or spot treatments Emulsifiable concentrates are usually clear but emulsions lookindoors in out-of-sight areas (behind equipment, in wall voids similar to milk. Finished sprays are emulsions or solutionsand so on) which remain dry. The residual pesticidal activity diluted to field strength. Unlike solutions, most emulsionsof dust is normally fairly long, provided the dust stays dry, but need a little periodic agitation to keep the concentrate fromquickly loses it toxicity in the presence of moisture. They don’t separating out of the water. Emulsions are used for residualadhere well to vertical surfaces. treatments. Pests that contact these surfaces are killed byDusts are used on people during mass delousing operations to the pesticidal residue. Emulsions may damage aluminium,control outbreaks of lice borne diseases. Dusts are also used varnish, and painted surfaces due to the action of solvents suchfor flea control during plague outbreak. Dusts aren’t generally as Xylene. Emulsions may also be corrosive to metal sprayersabsorbed through the skin, but may be dangerous if inhaled and their fittings and hence sprayers made of stainless steel,into the respiratory tract. aluminium or other non-corrosive materials should be used.Granules : These are basically the same as dust formulation, Oil Solutions : These formulations consist of a technical gradeexcept the carrier particles are larger and thus don’t stick to pesticide dissolved in a solvent such as kerosene or dieselleaves allowing penetration in dense foliage. This is a real oil. Solutions are available as ready-to-use formulations (foradvantage when the pesticide must reach the water surface for example ordinary household fly and mosquito sprays with amosquito control in vegetated swamps, or if it must get to the low percentage of pesticide) and as solution concentrates. Theseground surface through trees and shrubs for chigger control. concentrates contain a high percentage of insecticide and mustGranules are also available in timed-release formulations that ordinarily be diluted in oil or another suitable solvent. Somerelease a dosage of the pesticide over an extended period of concentrates are used without dilution in Ultra Low Volumetime. Other advantages of using granules are that they provide (ULV) applications. Oil solutions applied as finished sprayslonger lasting effects and their use results in less drift than often kill insects on contact, since the oil helps the pesticidegenerally occurs with liquids or dusts. penetrate the insect’s waxy body wall.The percentage of insecticide in granules and pellets varies Ultra-Low Volume (ULV) : While most items of ULV pesticide • 910 •
  • 11. dispersal equipment use the readily available solutions or Ticks depending on the formulation. Care should be takentechnical grade formulations, there are special ULV formulations while handling aerosol cans since they can explode if puncturedavailable for e.g. Deltamethrin 1.25 ULV etc. or overheated, even after the pesticide has been dispensed.Gaseous formulations : Gases are primarily used in Common insecticides used as aerosols are Pyrethroids,fumigation operations. They may be prepared as liquefied Malathion, DDVP and repellents like DEET and DEPA. Thesegases and packaged in pressure containers or in a material are used for disinfesting aircrafts, tents, rooms, other smallform that reacts with the moisture in the air to form a gas. enclosures, uniforms and for topical application. An emissionThe gas molecules can penetrate cracks, crevices and tightly of nearly 15 seconds is enough for a 100 m3 space.packed material. Gases are the most dangerous pesticides used Equipmentand hence special safety equipment and training are necessarywhen using gases and must never be attempted except by Equipment used for vector control can be broadly classified astrained pest management personnel operating in pairs. One ground equipment and equipment used for aerial applications.of the common gaseous formulations viz. Calcium cyanide (a) Ground Equipment(powder) and Aluminium phosphide (tablet) are used for rodent (i) Sprays for production of fine or coarse spray which may becontrol. either manually operated or power operated.Special formulations (ii) Sprayers for the production of mist which may be eitherResin Strips : Pesticide-impregnated resin strips release with gaseous energy nozzles (manual operated or powervapours as they are heated or exposed to normal room operated) or with centrifugal nozzles.temperatures. The use of resin strips in rooms occupied by (iii) Devises for the production of aerosols which maythe young, the elderly or in food preparation and food serving be mechanical, thermal or gaseous energy aerosolareas is strictly prohibited. generators. (iv) Dusting equipment which may be manually operated orBaits : Baits are commonly used to manage scavenging pests power operated.such as rodents, ants, flies, and cockroaches, which are (v) Applicators for granules and pellets, manually or powerparticularly difficult to manage with standard techniques. operated.Baits consist of the toxicant mixed with a food attractive to thetarget pest or with water. For this reason, baits made with local (b) Aerial Equipmentfoods are normally more effective than premixed formulations. Equipment for aerial sprays is essentially the same but withRecent development is the use of pheromone Muscalure with certain modifications. The equipment in common use is theImidacloprid as bait for houseflies. boom and nozzle system.Gel : One of the special formulations developed for use against Sprayerscockroaches is Gel formulation. Gels comprise some foodattractant mixed with the toxicant and some stabilizing agents. The equipment commonly used for spraying various insecticidalExamples are Fipronil and Imidacloprid Gels marketed against formulations are the hand operated sprayers, power operatedcockroaches. sprayers, aerosol dispensers, fog generators and dusters.Shampoo : This formulation has been specially developed (a) Hand Operatedfor use against head lice infestation. Permethrin is the most These are hand sprayers, knapsack sprayer and compressioncommon ingredient of the commercially available anti-lice sprayer.Shampoo formulations worldwide. (i) Hand Sprayer : The hand sprayer is used for space sprayingBeads / Pellets / Briquettes : Small floating beads, pellets or of small apartments. It is provided with a small can for holdingbriquettes incorporating biocides - Bti and B sphaericus have ½ to 1½ litres of spray fluid and a cylindrical plunger type airbeen developed against Anopheline larvae. These formulations pump. The nozzle size is less than 0.4 mm in order to produce acan be made as controlled release formulations as well. fine spray. The simplest form is the familiar ‘flit gun’ producingPaints and Lacquers : These can be used for incorporation intermittent spray. A number of other light hand sprayers haveof insecticides especially for control of pests on ships. These been designed, which can be pressurized in the manner ofpreparations remain effective for long periods. The new compression sprayers and are used to produce a mist or fineinsecticide, Imidacloprid is also available as a paint formulation droplet spray.against houseflies. (ii) Knapsack Sprayer : This is designed to fit on to the backMats / Coils : These are special formulations which have been of the operator and usually has a capacity of 15 to 20 litres.developed as controlled release formulation for indoor use It incorporates a light but powerful diaphragm pump actuatedagainst mosquitoes. These have synthetic pyrethroids such as by a lever carried forward to the operator’s hand where it isAllethrin, which acts as toxicant to knock down the mosquitoes worked by an up-and-down movement. These sprayers are usedwhen used indoors. both for larviciding and residual spraying. The nozzle size used for residual spraying varies between 0.78 to 1.0 mm so as toAerosols : Aerosols are pressurized cans containing a small produce a coarse spray.amount of pesticide driven through a small nozzle. They’recommonly used as space sprays for flying insects viz. (iii) Compression Pneumatic Sprayer : This is the commonestmosquitoes and houseflies and as residual sprays for Mites/ type of equipment used in National Vector Borne Diseases Control Programme for the application of insecticides. It has • 911 •
  • 12. a hand operated pump incorporated to build up adequate (d) Wash your overalls and other protective clothing at thepressure. When the pressure is released by a trigger on the end of each working day in soap and water and keep themlance, the liquid is forced out from the tank to the nozzle by separate from the rest of the family’s clothes.the compressed air and a continuous spray of the insecticide (e) If the insecticide gets on your skin, wash off immediatelyformulation is produced. It is slung over the shoulder with with soap and water.one strap or may be carried on the back with two straps. It is (f) Change your clothes immediately if they becomeoperated by one person. contaminated with insecticides.(b) Power Operated Sprayers (g) Inform your supervisor immediately, if you do not feel well.These are useful for application of insecticides over large areas. (h) Wear protective clothing (Fig. - 3) :These are hydraulic sprayers in which the spray liquid is expelled - Broad rim hat (protects head, face and neck from sprayto the nozzle by positive displacement by the plunger pump. droplets).Insecticide tanks built into a truck or mounted over a hand - Goggles or face shield (protects face and eyes againsttrolley are connected directly to a power operated compressor. spray fall-out).By means of a long hose the spraying fluid is conveyed under - Face mask (protects nose and mouth from airbornepressure through the lance to the nozzle. particles of the spray fall-out).(c) Insecticidal Fog Generators - Long sleeved overalls (Keep overalls outside of boots).Several types of fog generators are now available for the - Rubber gloves.production of insecticidal fogs in the open on a large scale. - Boots.In these fogging machines the oily solution of the insecticide Preparationsis finely atomized by the powerful blast of hot exhaust gases The Household : Inform the householder of the sprayingfrom a petrol engine. schedule and the purpose of spraying, giving them time to(d) Aerosol Dispensers prepare and vacate the house. Occupants MUST leave housesThese are used for disinfestations of aircrafts, tents, rooms before spraying. Rooms occupied by sick people who cannotand similar small enclosures. It contains insecticide and a be moved must NOT be sprayed. Remove all household items,propellant. Common aerosols contain Synthetic pyrethroids including water, food, cooking utensils and toys from the house.or their combination, which are routinely used for mosquito, Move and cover, or take out the furniture to allow easy accesscockroaches and fly control. for spraying walls. Items that can not be removed should be well covered.(e) Dust Gun Equipment : Indoor residual spraying of insecticides isInsecticidal dusts are applied against lice and fleas in rat normally done using hand-operated compression sprayers.burrows or on water surfaces as dry powders diluted with inert Before starting a spray operation, the equipment must bedusts. Small light weight guns are used for mass delousing of checked. Faulty sprayers may result in poor control or over-infested people. treatment. Examine the sprayer visually to ensure that all partsResidual Spraying are present, assembled correctly and are in good condition (Fig. - 4).This is the application of insecticides to surfaces so that theinsecticide particles remain on the surface in the form, size and Fig. - 3 : Protective Fig. - 4 : Hand-operatedquantity suitable for insects to pick up on contact and sufficient clothing for spraying compression sprayerto exert a lethal effect over a long period. Organochlorine,Organophosphorus, Synthetic pyrethroids and Carbamate A: Hat H.Hosecompounds can thus be applied on the inside walls of houses B: Goggles G.Strainerand also on thick bushes in forests. The type of surface to C: Mask D.Pump (handle)which an insecticide is applied influences its toxicity againstinsects and its persistence. Solutions and emulsions quickly E.Pressure gaugeget soaked in the absorbent surfaces of soft bricks and mud D: Long J.Triggerwalls which take in a large portion of insecticidal material Sleeved Overalls C.Liddeposited on them; but when suspended in water it remainsover the surface after the water evaporates or gets absorbed. The B. A.Sprayer tanknozzles of sprayers used for residual spraying must conform to E: Rubber Shoulderthe need of having a droplet size which is neither too large nor Gloves strap F.Lancetoo small. Similarly, safety precautions should be observed, asfollows, while spraying as per standard WHO guidelines : F: Boots K. Foot rest(a) Do not eat, drink or smoke while working. I.Nozzle(b) Wash your hands and face with soap and water after Nozzle body spraying and before eating, smoking or drinking. Nozzle tip(c) Shower or bathe at the end of every day’s work and change Nozzle cap into clean clothes. • 912 •
  • 13. A. Sprayer tank (c) Operate the pump using both hands and with foot onB. Shoulder strap the footrest. Pump to the working pressure of 55 psiC. Lid (Fig. - 7).D. Pump (handle)E. Pressure gauge Fig. - 7F. LanceG. StrainerH. HoseI. Nozzle - check correct type of nozzle is fitted and is not damaged or worn (flat fan nozzle with 55º to 60º swath and 0.75 l/min flow rate at 700 g/ sq cm).J. Trigger on/off valve. Is the strainer inside valve handle clean?K. FootrestBefore using an insecticide, use clean water to ensure that theequipment operates properly and does not leak. Wear protectiveclothing. To check, follow the steps below :(a) Pour clean water into the tank (never fill tank more than 3/4 full) (Fig. - 5). Fig. - 5 (d) Check tank is holding pressure. Listen for hissing sound of escaping air (Fig. - 8). Fig. - 8(b) Fit the lid. Turn the handle to lock the lid in position (Fig. - 6). (e) Check to make sure there are no leaks along lance and Fig. - 6 hose, especially where hose joins tank and trigger on/off valve (Fig. - 9). Fig. - 9 • 913 •
  • 14. (f) Operate trigger on/off valve to make sure that spray is container with water for several hours before the blockage is emitted from the nozzle (Fig. - 10). removed by a very soft toothbrush. NEVER clean nozzle with a hard pin or piece of wire and NEVER put a nozzle to your Fig. - 10 mouth to blow through it. Mixing, Handling and Spray Techniques Prepare the insecticide spray according to the manufacturer’s instructions. The insecticide may be mixed separately in a bucket and poured into the sprayer. Water soluble sachets, tablets and insecticides granules are added directly to the water filled tank. These formulations mix readily with water and reduce the hazards associated with handling and mixing in a separate container. When the sprayer has been filled with water to the maximum level indicated on the tank, the lid of the tank is fitted and the sprayer pumped to a pressure of 55 psi by pumping 55 times (700 g/sq cm). The contents of the tank should be thoroughly mixed by shaking the tank before starting to spray (Fig. - 12). Fig. - 12(g) Check the spray pattern from the nozzle by spraying a dry wall surface. Look to see that the pattern is even and without streaks. Ensure nozzle does not drip when trigger on-off valve is released (Fig. - 11). Fig. - 11 Spraying in a room should commence from the backside of a door clockwise completing the plain surfaces of walls. Then the crevices on the walls and inside portion of windows etc. should be sprayed. Thereafter the pillars, under surfaces of furniture and lastly the ceilings should be taken for spray.(h) Calibrate the nozzle with water in the tank. Pump to 55 Spray is done from roof to floor, using downward motion, to psi (700 g/ sq cm). Open the trigger on-off valve for one complete one swath; then stepping sideways and spraying minute, collect the discharge and measure the amount in a upwards from floor to roof. Spray is applied in vertical swaths measuring jug. Empty the jug. Discharge for a further one 52-56 cm wide. Swaths should overlap by 5 cm and spraying minute and measure the amount. Repeat again and calculate should be undertaken as shown in Fig. - 13. Normal swath the average of the three, one-minute measurements. coverage will take 2.7 sec if height of wall is assumed to beWith the above procedure, the average discharge of an 8002 3 meters and hence in one minute 22-23 swaths will cover anozzle is about 750 ml per minute. If the discharge is incorrect, wall of 10-11 metres length and 3 metres height i.e. 30 - 33 sqcheck the nozzle and the screen filters to ensure they are not m. It takes about 5 minutes to spray a house with an averageclogged. If necessary replace nozzle. Repeat the calibration. surface area of 150 sq m.If the nozzle is clogged : The opening in a nozzle is very smalland must not be damaged. Clogged nozzles should be put in a • 914 •
  • 15. Time your spray speed to cover one meter every 2.2 seconds, Fig. - 13 i.e. 4.5 seconds for a 2 m high wall. Timing may be aided by mentally counting “one thousand and one - one thousand and two - one thousand and three -…”. Adjust the mental counting procedure according to the local language (Fig. - 15). If spray stops due to a blockage in nozzle, unscrew the nozzle cap, remove blocked nozzle and replace with a new one. The blocked nozzle should be cleaned as explained above. Do not let spray drip on the floor. Re-pressurize the tank when the pressure falls. Fig. - 15To ensure the correct swath width, keep the spray tip about45 cm from the wall. Lean forwards as you spray from top ofthe wall and move back as you bring the nozzle downwards(Fig. - 14). Fig. - 14 Procedures after Spraying (a) Advise the occupants to stay outside until the spray is dry. (b) Instruct the householder to sweep or mop the floor before children or pets are allowed to re-enter. (c) Instruct the householder not to clean the sprayed surfaces. Disposal of Remains of Insecticides and Empty Packaging: At the end of the day’s work, put the washings from the sprayer into pit latrines, if available, or into pits dug especially for this purpose and away from sources of drinking water. Dilute any insecticide with more water before putting into pits. It is advisable to prepare only sufficient insecticidal solution to avoid disposal of remaining insecticidal solution. Never pour the remaining insecticide into rivers, pools or drinking water sources. All empty packaging should be returned to the supervisor for SAFE disposal. Never re-use empty insecticide containers. Empty insecticide containers should NOT be burned or buried. Maintenance of Equipment : After completing the day’s work, de-pressurize the tank and empty any remaining insecticide, following the instructions given in the previous section. Clean the tank as explained below :The flow of liquid from the nozzle tip at 700 g/sq cm pressure ●● De-pressurize the tank.is 750 ml/minute. Hence 30 sq m surface will be covered with ●● Fill the tank half-full with clean water.750 ml of the insecticide solution. ●● Replace the lid. • 915 •
  • 16. ●● Shake the tank so all inside surfaces are washed Fig. - 19 (Fig. - 16). Fig. - 16 ●● With lid open, turn tank upside down, open the on/off valve and let all the water drain out of the hose and lance. ●● Ensure the lance is parked to protect nozzle when not in use. ●● When storing the sprayer for a long period, hang it upside down with lid open to allow air circulation. Allow lance to hang from D-ring on the tank with the trigger valve kept open (Fig. - 20). Fig. - 20●● Pump up to 700 g/ sq cm pressure. Spray water through nozzle (Fig. - 17). Fig. - 17●● De-pressurize the tank and pour out any remaining water into pit latrines or into a pit away from sources of water.●● Unscrew trigger on/off valve handle and check and clean the strainer.●● Reassemble the trigger on/off valve (Fig. - 18). Space Spraying Fig. - 18 It is an ideal method for bringing about rapid control of vectors in emergency or epidemic situations and may also be used for seasonal control of flying insect pests or vectors. An additional objective may be to reduce or interrupt the transmission cycle of insect-borne diseases. However, it may not be ideal for all vectors or situations and as such may not be an economical method of control. Among the disease vectors affecting public health, the most important and widespread are mosqui­ oes, t●● Remove the nozzle tip and wash houseflies, sandflies and other biting flies; some of these may●● Refit the nozzle be tar­ eted for space treatment. g●● Clean the outside of tank. Immediate killing of actively flying insects requires a cloud of insecticide droplets that they will encounter in flight. To • 916 •
  • 17. be cost-effective and obtain good biological efficacy, space Cold Fogspraying requires : The cold fog is produced by a special device (cold fogger) that(a) Knowledge of the behaviour and biology of the target breaks up the chemical into microscopic droplets by mechanical species - to understand where and when space treatments means, basically with a high-pressure pump and an extremely will be effective; fine nozzle. The spray droplets are generated without any(b) Knowledge of insecticides and formulations most suitable external heat. With cold fogs, the volume of spray is kept to for space spraying; a minimum. Ultra-low-volume insecticide formulations are(c) Knowledge of pesticide application technology - to know commonly used for such applications. The cold fogger may which equip­ ent is needed and how to use it; and m dispense formulations in a very concentrated form and generate(d) Monitoring and surveillance of the target species and the droplets (usually in the 5-30 micron diameter range) in a vector-borne disease problem to evaluate the efficacy of precise manner. However, its ability to penetrate dense foliage the programme. or obstacles is not as good as that of the thermal fogging. ColdA space spray - technically a fog (sometimes referred to as an fogging is sometimes called Ultra Low Volume (ULV) treatmentaerosol) is a liquid insecticide dispersed into the air in the form as it allows the utilization of only a very small amount ofof hundreds of millions of tiny droplets less than 50 μm in chemical for coverage of a large area.diameter with a view to cause by contact, immediate knock Like thermal fogging, cold fogging also does not have lastingdown of the flying or resting insects in confined spaces. Space residual effects. It is, therefore, essential to carry out fogging atsprays, even when they settle on surfaces do not have much the time when the vectors are most active to hit them directly.residual action. It is only effective while the droplets remain Advantagesairborne. Therefore, they have to be repeated at frequentintervals. Space sprays are applied mainly as thermal fogs or ●● The amount of diluents is kept to a minimum, resulting incold fogs. lower appli­ ation cost and increased acceptability. Some c formulations are ready to use, thereby reducing operatorThermal Fog exposureThermal fog is produced by special devices known as thermal ●● Mostly water-based and water-diluted formulationsfoggers that use heat to break up the chemical into very small are used which pose a low fire hazard and are moredroplets (usually in 5-30 µm diameter range) which then environmental friendlydisperse in the air. When the chemical (usually diluted with ●● Application is more efficient because a lower volume ofoil-based carrier) is heated, it is vaporized in a combustion liquid is appliedchamber and then expelled via an outlet tube to form a dense ●● No traffic hazard as the spray cloud is nearly invisiblefog cloud when it condenses on contact with cool ambient air. DisadvantagesThe insecticide used in thermal fogs is diluted in a carrier ●● Dispersal of the spray cloud is difficult to observeliquid, which is usually oil-based. Hot gas is used to heat the ●● Higher technical skills and regular calibration are requiredpesticide spray, decreasing the viscosity of the oil carrier and for efficient operation of equipment.vaporizing it. When it leaves the nozzle, the vapour hits colder Space Spray Equipmentair and condenses to form a dense white cloud of fog. Most of Selection of appropriate equipment for space spraying dependsthe droplets are smaller than 20 µm. The droplet size is affected on the size and accessibility of the target area as well as theby the interaction between the formulation, the flow rate and human resources and operational capacity of the programme.the temperature at the nozzle (usually > 500°C). The volume Sometimes smaller machines may be needed in conjunctionof spray mix­ ure applied in vector control is usually 5-10 litres t with vehicle-mounted equipment to treat narrow pathways andper hectare, with an absolute maximum of 50 litres per hectare. other areas inaccessible to vehicles or sheltered from prevailingThe hot emission gas is obtained from engine exhaust, friction air movements. Cold fog equipment is recommended whereplate/engine exhaust or from a pulse jet engine. thermal fogs may cause a traffic hazard. Aerial applicationAdvantages of space sprays may be justified where access with ground●● Easily visible fog, so dispersal and penetration can be equipment is difficult and/or extensive areas need to be treated readily observed and monitored; very quickly.●● Good public relations in some circumstances as people can Equipment for Thermal Fogging see some­ hing being done about the problem; and t●● Low concentration of active ingredient in the spray mixture Hand-carried Thermal Foggers : These are used for treating and reduced operator exposure. houses and certain outdoor areas of limited size or accessibility,Disadvantages e.g. markets, hotel grounds and parks. There are two types of hand-carried thermal foggers; pulse jet and fric­ ion plate. t●● Large volumes of organic solvents are used as diluents, which may have bad odour and result in staining; Vehicle-mounted Thermal Foggers : Large thermal fog●● High cost of diluents and spray application; generators use an air-cooled motor to run an air blower, fuel●● Householders may object and obstruct penetration of fog pump and insecticide pump. Air from the “roots type air blower” into houses by closing windows and doors; is delivered into the combustion chamber. There it is mixed with●● Fire risk from machinery operating at very high gasoline vapour and ignited so that temperatures reach 426- temperatures with flam­ able solvents; and m 648°C. The diluted insecticide liquid is pumped via a simple flow●● Can cause traffic hazards in urban areas. delivery valve and injected into a cup in the fog head or directly • 917 •
  • 18. into the nozzle. The insecticide liquid is vaporized by the blast systems.of hot gases. Despite this high tempera­ ure, insecticides show t Insecticide Products for Space Sprayingvery little degradation of active ingredient. This is because thetime spent at that temperature is only a fraction of a second, Space-spraying formulations are generally oil-based. Thewhich is not long enough to cause serious degradation. The oil carrier inhibits evaporation of small fog droplets. Onlyhot gases then pass out of the machine. As the hot oil vapour insecticide products with high flash points are used for thermalis discharged through a relatively large nozzle into the cooler fogging. Diesel is used as a carrier for thermal fogging, butoutside air, it condenses to form very small droplets of thick creates a thick smoke and oily deposits, which may lead towhite fog. Delivery rates of up to 10 litres per minute can be public rejection. For environmental reasons, water-basedachieved with larger machines. formulations have been made available in recent years. These formulations may also contain substances that prevent rapidAircraft Application of Thermal Fogs : For aircraft application evaporation. Table - 3 lists selected insecticides suitable forof thermal fogs, the diluted insecticide formula­ ion is fed into t space spraying against mosquitoes. These insecticides may alsothe aircraft exhaust. The exhaust is adapted with vanes to swirl be used against other insect pests and vectors, but differentthe fog droplets as they are formed. The application of thermal dosages may be required.fogs by aircraft is very limited. Space Spray Treatments - General ConsiderationsEquipment for Cold Fog Application Optimum Droplet Size : Space treatments are only effectiveHand-carried Cold Foggers : Most of these machines have while the droplets remain airborne. Droplets fall by gravity andgasoline engine or electric operated which drives a blower some are deposited on horizontal surfaces while the majority isunit to discharge air through the nozzle. Air may also slightly lost to the atmosphere especially in outdoor spraying. Dropletspressurize the insecticide formulation tank so that the liquid bigger than 30 µm in diameter are less effective as they do notis fed via a restrictor to the nozzle. However, negative pressure remain airborne for sufficient time. Droplets smaller than 5 µmgenerated by the air flow passing through the nozzle allows in diam­ ter do not readily come in contact with flying insects, eliquid to flow from the tank. In addition to hand-carried units, as the movement of the smallest droplets is affected by the airknapsack cold fogging units are also available as are several turbulence created by the insect’s flight. It is generally acceptedelectrically driven models. that droplets should be generated in the range of 10-30 µmVehicle-mounted Cold Foggers : A high volume air blower so that even with some evaporation and after some time, theyforces air at a rate of approximately 6 m3 per minute at low remain in the correct range for optimal airborne suspensionpressure to nozzle. The pesticide container may be pressurized and insect impact. The optimum droplet size for space sprayingto force the formulation to the nozzle, or positive-displacement against mosquitoes is 10-20 µm.pumps may be used. Spray Concentration : For a flying insect to be killed, itAlternatively a high-pressure, low-volume air source is used must acquire a lethal dose of insecticide in the droplets thatwith an air compressor, rather than a blower. On these machines, impact on it. The lower the concentration of active ingredient,nozzles ranging from the standard industry “paint gun nozzle” the larger the number of droplets of a given size required toto proprietary nozzles that atomize well up to a flow rate of 0.5 achieve a lethal dose. Ultra-low-volume spraying aims, largelylitres per minute are available. Another design uses a rotary for operational reasons, to minimize the total volume of dilutednozzle coupled with an electric motor which operates at a very insecticide applied (usually < 2 litres per hectare).high speed. Wind Speed : Wind speed has a profound effect on dropletAircraft Application of Cold Fogs : Both fixed-wing aircraft distribution and impingement on insects. Spraying should notand helicopters have been used to apply cold fogs. Conventional take place when wind speed exceeds 15 km/hour. The type oflow-volume nozzles (e.g. flat fan) have been used on fixed wing terrain and vegetation affects air movement and hence theaircraft to create fine sprays, using moderate or high pressures. distribution of the droplets. In open terrain with relativelyHowever, the droplet spectrum is generally poor so preference sparse vegetation, wider effective swaths can be obtained thanis given to the use of rotary atomizers or very-high-pressure in urban areas where the obstruction of buildings alters the Table - 3 : Insecticides Used for Space Spraying S No. Insecticide Dilution Equipment required Remarks 1 Pyrethrum 2% Extract 1 litre in 19 litre Flit gun/ Thermal For space spray indoors (Keep rooms Diesel (0.1%) Fogging machine closed for 30 min) or outdoors 2 Pyrethrum 2% EC 1 litre in 19 litre Water ULV Fogging machine For space spray indoors 3 Malathion Tech 5 litres in 95 litre Thermal Fogging For space spray outdoors Diesel (5%) machine 4 Deltamethrin 1.25 ULV 1 litre in 199 Thermal Fogging For space spray outdoors litre Diesel machine 5 Deltamethrin 1.25 ULV 1 litre in 19 litre Diesel ULV Fogging machine For space spray outdoors 6 Deltamethrin 1.25 ULV 1 litre in 19 litre Water ULV Fogging machine For space spray indoors • 918 •
  • 19. flow of air. reoccupation.Wind direction : With vehicle-mounted and aerial spraying ●● Close all doors and windows before spraying and keep themthe spray route must take account of the wind direction to closed for 30 minutes after spraying to ensure maximummaximize the distribution of the spray throughout the target efficacy.area. Fig. - 21 illustrates the spray application route relative to ●● Spray operators should work backwards and away fromwind direction. the fog to minimize exposure. ●● For small single-storey houses, the spray can be delivered Fig. - 21 : Spray Application Route from the front door or through an open window without having to enter every room of the house, provided that Path of spraying adequate dispersal of the insecticide droplets can be achieved. ●● For large single-storey buildings, it may be necessary to apply the spray room by room, beginning at the back of the building and working towards the front. ●● For multi-storey buildings, spraying is carried out from top floor to the ground floor and from the back of the building to the front. This ensures that the operator has good visibility at all times. Outdoor Ground FoggingWind direction Spray drift Advanced route planning should precede outdoor ground fogging operations and may require a combination of vehicle- mounted and hand carried or knapsack equipment in areas with difficult or limited vehicle access. Consideration must also be given to the following : ●● Spraying should not be undertaken when it is raining, when winds exceed 15 km/hour, or in the heat of the day. ●● Doors and windows of houses and other buildings should be open to allow penetration of the spray cloud for improved efficacy.Temperature Effects : In direct sunlight the ground is heated. ●● For vehicle-mounted equipment, in areas where the roadsThis causes air to rise. In the middle of the day, outdoor space are narrow and the houses are close to the roadside, thespraying will largely be wasted as the spray droplets will tend to spray should be directed backwards from the vehicle. Inrise upwards rather than drift horizontally. Ideally an inversion areas where the roads are wide, with buildings far from theis needed, i.e. colder air closer to the ground. This generally roadside, the vehicle should be driven close to the roadsideoccurs early in the morning after the ground temperature has and the spray should be directed at an angle (downwind)fallen during the night, but can also occur in the evening when to the road rather than directly behind the vehicle.the sun has set and ground temperatures begin to fall. ●● The nozzle of vehicle-mounted cold fog machines mayTime of Treatment : Knowledge of the time of peak flight be directed upwards at an angle when there are barriersactivity of the target species is crucial to ensure that space that impede airflow, e.g. boundary walls and fences; fortreatments are planned to coincide, as far as possible, with vehicle-mounted thermal foggers, the nozzle should bethese times. Fortunately, peak flight activity of many vectors directed horizontally.is around dusk and/or dawn, when weather conditions are ●● A track spacing of 50 metres is generally recommended,often favourable for space treatment. Aedes aegypti and Aedes with the vehicle moving upwind so that the fog driftsalbopictus, mosquito vectors of Dengue fever and Chikungunya downwind away from it and the operators.are active during daytime with peak flight activity in the Aerial Application of Fogs : Suppression of vector populationsmorning and afternoon. With these species, a compromise is over large areas can be carried out using space sprays releasedusually made outdoors by spraying in the early morning or late from aircraft, especially over areas where access with groundafternoon. The timing is less important if indoor spraying is equipment is difficult and extensive areas need to be treatedconducted. very rapidly.Indoor Fogging EvaluationPersonnel conducting this work require training on the safety Evaluation of the efficacy of spray operations is carried outmeasures to be followed. Several rules apply : using techniques that are largely specific to the target insect.●● Protect all water containers and foodstuffs. Space sprays are transient and only insects flying at the time●● Remove fish or cover fish tanks. of the application are affected.●● Ensure all occupants and animals remain outside the Area Spraying house during spraying and stay outside for 30 minutes This is carried out for treatment of land against mites and ticks after spraying. Ensure that the building is ventilated before and also as an anti-larval measure over vast water surfaces. • 919 •
  • 20. Against mites and ticks, suspensions are used on land and Types : Resistance is of two types i.e. physiological andvegetation; WDP is used for anti-larval treatment of lakes and behaviouristic. Physiological resistance is the one describedswamps. Aerial spraying is resorted to for agricultural purposes above. Behaviouristic resistance means the development ofand sometimes for veterinary and rarely medical purposes. ability to avoid a lethal dose. This term is applied most often toDusts are applied to manure yards and dry refuse yards to mosquitoes in relation to DDT.control flies and other pests. For all such uses, power driven Resistance Mechanismssprayers and dust guns are used. The larvicidal oils are applied Metabolic Resistance : This is the most common resistanceby spraying it on the surface of water by means of a knap-sack mechanism encountered amongst insects, based onsprayer or hand pumps or by a mop stick. detoxification enzymes. In resistant strains, these enzymesResistance of Vectors to Insecticides are generally more enhanced thus enabling the insects toHistory : Ever since the introduction of the potent synthetic metabolize or degrade the insecticide before their lethal effectinsecticides into public health programmes at the close of the is exerted. The enzyme systems involved in these processesSecond World War, the main problem has been the development are Esterases, Monooxygenases and Glutathione-S-tranferasesof resistance to them by the arthropods they formerly controlled. (Table - 4).In 1947, DDT resistance was discovered in the housefly and (i) Esterases - Dominant mechanism of resistance conferringCulex molestus in Italy. In 1951, DDT resistance was noticed in resistance to OP compounds. It also affects Pyrethroidsbody louse in Korea and in Anopheles sacharovi in Greece. In and Carbamtes.1955, Dieldrin resistance was discovered in Anopheles gambiae (ii) Monooxygenases are importantly involved in the resistancein Northern Nigeria. In 1959, in Western India the oriental rat mechanism in insects to Pyrethroid class of insecticides. Itflea was found to have developed resistance to DDT. The number also affects DDT and OPs.of arthropods showing resistance is on the increase. (iii) Glutathion S transferase - It has been implicated in DDTDefinition : Resistance is defined as “the development of an resistance.ability in a strain of insects to tolerate doses of toxicants which Target - Site Resistance : This is the second most commonwould prove lethal to the majority of individuals in a normal resistance mechanism encountered in insects. The site of actionpopulation of the same species”. A more pertinent definition of the insecticide is modified so that the insecticide no longerof resistance promoted by the Insecticide Resistance Action binds effectively at that site. Resistance to DDT and pyrethroidsCommittee (IRAC) is “the selection of a heritable characteristic is due to the modified gene Kdr, which leads to reduction in thein an insect population that results in the repeated failure of sensitivity of the site to the binding of DDT and Pyrethroids. Onan insecticide product to provide the intended level of control the other hand, an altered site of action as a cause of resistancewhen used as recommended”. It is important to remember that to Organophosphates (OPs) and Carbamates has been definitelyresistance does not mean that it is impossible to control the established with cholinesterase inhibitors. In these cases,population. mutated forms of AChE (MACE - modified acetylcholinesterase) are produced that is inhibited more slowly than the normalThe word tolerance is normally used when the increase in enzyme in susceptible strains. This produces resistance againstLC50 is less than the indicated minimum for the tests, but is a large number of compounds of the OPs and Carbamates andnevertheless statistically significant. It is generally due to sub- the resultant extensive cross-resistance which makes it alethal exposure to insecticide and is not passed on to offspring. serious type of resistance.Vigour tolerance is a term, which has been applied to enhancedinsecticidal tolerance resulting from extra vigour of the strain Reduced Penetration : Not a major resistance mechanism,rather than from any specific defence mechanism. may contribute to the overall development of resistance to an insecticide. Modification in cuticle (applicable for contact poison) or digestive tract linings (in case of stomach poisons) Table - 4 : Biochemical resistance mechanisms conferring resistance to important classes of insecticides in mosquitoes (dot size gives the relative impact of the mechanism on resistance) Biochemical Mechanism of Resistance Metabolic Target-site GSH-S Esterases Monooxygenases kdr MACE transferases Pyrethroids DDT Carbamates Organo-phosphates Source : Prevention & management of insecticide resistance in vectors and pests of public health importance. Manual by Insecticide Resistance Action Committee (IRAC). • 920 •
  • 21. leads to prevention or reduced penetration of insecticides in the most pest problems. Natural enemies usually take longer tobody of the insects has been reported in a number of resistant suppress a pest population than other forms of pest controlinsects e.g. houseflies. and therefore often regarded as a disadvantage or limitation ofBehavioural Resistance : It is a modification in the behaviour biological control. It also may be difficult to “integrate” naturalof insects to avoid toxic doses of the insecticide. It is also a enemies when pesticides are still in use. Beneficial insectscontributory factor in development of resistance and not an are often highly sensitive to pesticides and their resurgenceimportant resistance mechanism. It may be stimulus dependent (recovery to pre-spray densities) is usually much slower than(when insects avoid insecticide treated surface) or independent that of pest populations. Rapid pest resurgence often leads to a(selective and sustained occupation of an untreated area). vicious cycle of continued chemical usage that prevents natural enemies from ever becoming re-established.Cross Resistance : Cross resistance occurs when a resistancemechanism that allows insects to resist one insecticide also The biological agents are broadly classified as Predators,confers resistance to insecticides of the same chemical class or Parasites and Pathogens.different chemical class which act on the same target site in the Predatorsinsect. e.g. kdr resistance to DDT and to Pyrethroids, OPs and Predators are insects or other insectivorous animals, each ofCarbamates due to altered AChE. which consumes much insect prey during its lifetime. PredatorsMultiple Resistance : It is a common type of resistance when are often large, active, and/or conspicuous in their behaviour,different resistance mechanisms are present simultaneously and are therefore more readily recognized than are parasites andin resistant insects. It may combine to produce resistance to pathogens. Most commonly used predators are the larvivorousmultiple classes of insecticides. fishes for the control of mosquitoes.Genetic Basis of Resistance : Resistance develops in arthropods Larvivorous Fish : There are areas and habitats whereafter a long period of insecticidal pressure. It is brought about by larvivorous fish, such as Gambusia affinis (Fig. - 22) and Poeciliathe accumulation of the contributing genes through successive reticulata (Fig. - 23), can make considerable contribution toselection with a number of insecticides, each of which confers vector control. The larvivorous efficiency of Gambusia is duesome cross-resistance. This is called polygenic or multiplicate to the fact that a single full grown fish eats about 100 to 300resistance. In contrast, the resistance may be due to a single mosquito larvae per day, is a surface feeder, hence it is suitablegene and bear no similarity to the complexities involved in the for feeding on both Anophelines and Culicines, is small andmultiplicate resistance. Monogenic resistant strains are more inedible and can tolerate salinity. Poecilia’s larvivorousvulnerable to counter measures such as addition of synergists; efficiency is due to its capability to negotiate margins of pondshence the importance of distinction between the two types. more easily, tolerate handling and transportation very well,Resistance genes may be dominant, semi-dominant or survives and reproduces when introduced into new waterrecessive; most of the resistance reported so far are either bodies, survives in new places (water bodies) and multipliessemi-dominant or recessive and therefore may be managed easily and can survive in good numbers for years and does noteffectively as compared to situations when resistance is require constant care.genetically dominant.Resistance Management : The factors that favour development Fig. - 22 : Gambusia affinisof resistance are frequency of application, dosage andpersistence of insecticide, rate of reproduction (short lifecycleand high rate of reproduction) and population isolation.Resistance management can be attained by rotation ofinsecticides, using mixture of insecticides at their optimumdosage (efficacy & persistence of the two insecticides beingmixed should be broadly similar) and fine scale mosaic (usingtwo insecticides in different houses in the same village).Biological ControlIntentional manipulation of populations of living beneficial Fig. - 23 : Poecilia reticulataorganisms, called natural enemies, in order to reduce thenumbers of pests or amount of damage is called BiologicalControl.Natural control strategies that employ biological agents forpest suppression are classified as biological control tactics. Inconventional usage, this term usually refers to the practice ofrearing and releasing natural enemies like parasites, predators,or pathogens. Biological control is a particularly appealing pestcontrol alternative because, unlike most other tactics, it doesnot always have to be reapplied each time a pest outbreakoccurs. However, Biological control is not a “quick fix” for • 921 •
  • 22. Release of fishes is done at the rate of 5-10 fish per linear leading to population control, reduction or elimination throughmeter. If the larval density is high up to 20 fishes can be the release of partially or completely sterile insects in sufficientreleased. Fishes should be released in the morning hours or in numbers to overcome the reproductive capability of thethe evening. natural population; and those leading to population control orCriteria for selecting a water body for a fish hatchery are : population replacement through the release of partially sterile●● It should be a permanent water body. or fully fertile genetically altered insects.●● Depth of water should be at least 1.5 metre or more. New genetic control methods, such as those involving sex●● Water should be confined and without big natural outlet. distortion mechanisms or the selection and release of strains●● The minimum size of water body should be at least refractory to pathogens, sensitive to selected ecological factors, 5m X 4m. The water body of 10 m X 5 m can support or susceptible to insecticides, are being tested under field 50,000 fish. conditions. However, unless some new and revolutionary ideas●● It should be free from other carnivorous fish. emerge, the genetic control measures so far known are capable●● Water should not be contaminated by chemical or other of achieving only “management” or “manipulation” of insect harmful substances. population rather than complete suppression or reduction in●● Easily accessible for daily or periodic inspection and for densities. collection of fish.●● De-weeding in ponds and shallow water bodies and Personal Protective Measures cleaning of margins should be carried out periodically. The role of personal protective measures in arthropod-borne disease control is to prevent the arthropod vector from bitingParasites and feeding on its host, whether susceptible or already infected,Parasites are those organisms which depend on their host for thereby blocking the chain of transmission of disease from oneshelter or food. Many parasites are very specific to the type host to another. Biting can be prevented either by protectiveof host insect they can attack, and they are not harmful to clothing or chemically by using appropriate repellents.humans. Although insect parasites are very common, theyare not well known because of their small size. Some of the Protective Clothingcategories of Parasites are as follows : Individual personal protection against bites of arthropods canNematodes : Nematode Romanomermis culicivorax and be achieved by wearing long trousers, rolled down sleeves ofR iyengari have been evaluated and have been found to give shirts, socks, shoes and anklets, particularly when going out onvariable control of mosquitoes. The mode of action of the patrols and exercises in areas heavily infested with arthropods.nematodes is presented in Fig. - 24. These measures will vary according to the nature of problem faced in a particular locality. Personal protective measures have Fig. - 24 : Mode of action of Romanomermis against already been described as part of control measures against mosquito larvae different arthropods elsewhere in this chapter. Repellents Eggs Pre-parasitic nematodes invade mosq larvae Laid in mud Insect repellents are chemicals which repel insects when 7 days applied to body surfaces or clothing. The suitability of substances for use as repellents is dependent primarily on Drops to Kills Exits through their inherent repellency and duration of effectiveness. The bottom larvae cuticle important factors are the ease of application on the skin; odour, Moults, mates & females appearance or feel on the skin e.g. oily or greasy; the likelihood start laying Eggs of being rubbed off, or absorbed by the skin; irritant effect or toxicity if absorbed; and its stability under high humidity, highFungi : Fungal agents Lagenidium and Culicinomyces have temperature, rain and perspiration. The efficacy may also beshown immense potential as mosquito larval control agents influenced by the amount of sweating, rubbing and the avidityand can be exploited for use against mosquitoes. of the insect itself. Moreover as is the case with insecticides,Pathogens repellents exhibit specificity of action so that some species of insects are more sensitive to one and some to other repellents.The pathogens which have been found promising are theBacterial agents’ Bacillus thuringiensis var israelensis and Common Repellents : The following compounds are amongBacillus sphaericus in mosquito larval control. However, these the most effective when used alone as repellents againsthave been classified as Biocides or Microbial insecticides one or more groups of arthropods : benzyl benzoate, DEET(discussed earlier). Viruses like Nuclear Polyhedrosis virus and (N, N-diethyl-m-tolumide), dibutyl phthalate, DEPA (di ethylIrido virus have also shown promise against mosquito larvae. phenyl acetamide), and Neem oil. Repellents are formulated as liquids, gels, creams and in pressurized containers. Some ofGenetic Control the common compounds are discussed below :This is defined as “the use of any condition or treatment that (a) N, N-diethyl m-toluamide (DEET) : DEET has been reportedcan reduce the reproductive potential of noxious forms by to be an outstanding all-purpose repellent. It provides 6-8 h ofaltering or replacing the hereditary material”. The various protection against mosquitoes, 2-3 hour against Chrysops, 9methods of genetic control fall into two general groups : those hour against Culicoids. It feels less oily on the skin than the • 922 •
  • 23. other repellents. DEET can also be used very effectively for (ii) Spraying / Impregnation : The chemical can be appliedimpregnation of clothing. In experiments conducted at AFMC to the entire clothing by spraying or the clothing can beit has been shown to provide repellence up to two launderings impregnated with a solution or emulsion of the repellent whenof the clothing. As a skin application DEET may be used for large quantities of clothing are required to be treated. Clothingprotection against mosquitoes, sand flies, fleas and other biting should be soaked in the solution, then wrung out lightly andDiptera. It is a good repellent against all haematophagous dried. DEPA is available as spray formulation for treatment ofarthropods and also against leeches. clothing.(b) Dibutyl Phthalate (DBP) : It is more persistent but Barrier Application : Considerable protection may also besomewhat less rapid repellent. When smeared on clothing, obtained by treating only the openings of the clothes insideits effect lasts up to 2-4 washes, ironing destroys it. It is the neckband and cuffs of shirts, inside the waistband, fly andspecifically useful against ticks and mites as it is an acaricidal, turn ups of trousers and on the socks above and inside theas well as a repellent. DBP is a good repellent against leeches shoes and below its tongue. These methods, called the barrierand Dimdam flies. application, are particularly useful when people go for amateur(c) Benzyl Benzoate : The oily liquid has a faintly pleasant camping or trekking or when sufficient supplies of repellentsaromatic odour and sharp bitter taste. It has been applied in are not available.5% emulsion to skin as repellent for many arthropods. Clothing Household Productsimpregnated with benzyl benzoate show repellence to fleas, Use of mosquito coils, vapourising mats, liquid vapouriserschiggers and other arthropods. A mixture of equal parts of consisting of pyrethroids is an important measure in reducingdiethyltoluamide and benzyl benzoate with the addition of man-vector contact. These products basically aim at deterringan emulisifier acts as a good impregnant for clothing against the insects from entering the rooms and with continued contacttrombiculid mites. bring about death of the exposed insects. The allergic risks(d) Diethyl phenyl acetamide (DEPA) : It is available as cream which these products pose on continued exposure especially toand sprays. It is a broad spectrum repellent and can be used for children necessitates adoption of safer preventive measures fortopical application against mosquitoes, ticks & mites or any personal protection.other haematophagous arthropod and leeches. It can also be Mosquito Netsapplied on clothing/uniform as repellent. It can withstand 2-3launderings and ironing. It matches DEET in its spectrum and Mosquito nets are very effective means of protection against theefficacy. bites of haematophagous arthropods. Untreated or insecticide treated nets may be used as per the availability. The bednetsApplication Procedures may be treated manually or may be purchased as pre-treatedSkin Application : Repellents like DEET and DEPA are applied nets.to the skin as cream formulation. These are generally effective Manually Treated Bednets : Insecticide treated bednets may beagainst such pests as midges, mosquitoes, sandflies and so manually treated with Synthetic pyrethroids like Deltamethrinon. A good repellent applied in this way gives protection from 2.5% SC or Cyfluthrin 05 EW. These nets have to be treatedinsect bites for about five to seven hours. every six months as per the procedure described in Box - 1.Impregnation of Clothing : Application to clothing is carried Long Lasting Insecticide Nets (LLINs) : The advancement inout when longer protection against insects is required. the insecticide treated net technology has seen the developmentApplication of DBP DEET or DEPA to clothing to protect one , of pretreated or Long Lasting Insecticide Nets (LLIN’s). Theseself from mites and ticks is much more persistent than skin nets may also be treated manually or may be pretreated withtreatment and remains effective for a period up to a month. insecticide Permethrin or Deltamethrin (Box 2). The shelf life of(i) Hand Application (Repellent Drill) : Hand Application of these nets is 5 years.repellent is the simplest way to treat the clothing. The fingersof one hand are dipped into the chemical in an open container Mechanical Control & Physical Controlor a few drops of the chemical are poured into one hand, both Use of flyswatters, fly traps for housefly control, use of licethe hands are rubbed together and then they are wiped lightly combs, glue traps for various pests like cockroaches andon the inside and also on the outside of all the openings of all rodents, other mechanical trapping devices used for othergarments to produce a thin layer of the chemical on them. The vectors are few examples of the use of this control option inchemical should be applied more particularly to the opening vector control.such as inside the neckband of shirts, turn ups of trousers and Physical control measures exploit devices which aim to controltops of socks turned inside out. 60 ml per man per fortnight of vectors by affecting them physically or their environment.DBP is enough to impregnate two shirts, two pairs of trousers, Sometimes they may be indistinguishable from environmental2 pairs of socks, anklets and two sets of underclothing. The or cultural methods. Fly electrocutors and use of temperatureapplication should be started a fortnight before the mite borne extremes (hot water for bedbug control, sun exposure anddisease (like scrub typhus) season in any area begins, and boiling in hot water of infested material for lice control) arerepeated every fortnight thereafter until the season lasts. This some physical control measures used in public health forshould be done on a parade as a drill supervised by a person who vector/ pest control.has had training and experience of the procedure. The repellentsDEET, DEPA require lesser quantities for impregnation. • 923 •
  • 24. Box - 1 : Steps for treatment of bednets (a) Measure the total area of the net in m2 . (2 x length x height + 2 breadth x height + length x breadth) in metres. Average area of a single net is 10 sq m. (b) Measure the absorption capacity ●● Measure 1 litre of water and take it in a tub. ●● Immerse the dry net, when completely wet, take it out by gently wringing the net to prevent dripping of water. ●● Measure the remaining water in the tub. 1 litre - the remaining water gives us the absorption capacity of the net. (c) Wash the net to be treated and dry it. (d) Calculate the dosage of the insecticide required ●● Deltamethrin 2.5% SC- dosage required 25 mg a.i. per m2. 1 ml of the 2.5% insecticide contains 25 mg; therefore the dosage will be 1ml per m2 to give the dosage of 25 mg a.i./m2. So if the net is of 10 m2 and the absorption capacity is say 500 ml then we need to add 10 ml of insecticide in 500 ml of water to give the reqd. dosage. ●● Cyfluthrin 05% EW- dosages required 50 mg a.i. / m2. 1 ml of the 05% insecticide contains 50 mg; therefore the dosage will be 1ml per m2 to give the dosage of 50 mg a.i. /m2. So if the net is of 10 m2 and the absorption capacity is say 500 ml then we need to add 10 ml of insecticide in 500 ml of water to give the reqd. dosage. (e) Put the net in the insecticide solution prepared as per the procedure given above and knead it well to ensure the net is completely soaked in soln. (f) Take out the net and spread it in shade, once semi dry it can be hung for drying. Box - 2 : Long Lasting Insecticide Nets (LLIN’s) A Long lasting insecticide net is a treated net which can withstand insecticidal efficacy up to at least 20 washes with more than 80% mortality after 24 hrs (95% Knockdown after 60 min). The treatment is done by either incorporating Insecticide ●● In the yarn itself which is made into textile and then used for making nets e.g. Olyset Net. -- It is Permethrin impregnated (500 mg a.i./m2 net) Polyethylene net. -- Washing cleans the surface and hence it is recommended to be heated up (i.e. sun dried) after washing for the active ingredient to “migrate ” to the surface. OR ●● By coating around fibres, e.g. Perma Net. -- It is a regular polyester net treated with 55 mg a.i./ m2 Deltamethrin. -- Resists multiple washes. -- Biological activity lasts as long as the net itself (3 to 4 years for polyester nets, 4 to 5 years for polyethylene ones). Manually treated LLIN ●● Any untreated net can be treated with long lasting formulation of Deltamethrin using K-O Tab. ●● Low cost as compared to pretreated nets.Legislative Control solving pest problems. These programs emphasize management rather than eradication. They take a broad ecological approachUse of laws and bye-laws to prevent / reduce propagation and to pest problems, focusing on all members of a pest complex inspread of vectors is an effective means of vector management, an effort to identify the optimum combination of control tacticsalthough stringent in approach. that will reduce vector populations below economic thresholdsIntegrated Vector Management and maintain these levels with the least possible impact on theDevelopment of resistance, effects on non-target organisms rest of the environment.and damage to the environment can all be minimized with IVM is a dynamic approach which requires a broad knowledgeselective and judicious use of multi-faceted control tactics of vector biology, ecology and behaviour on the one hand(Fig. - 25). This approach, commonly known as integrated and that of system analysis approach on the other so that acontrol, requires an understanding of ecological principles as variety of control measures, such as environmental, chemical,well as a thorough knowledge of the pest’s life history and biological, genetic and personal protective measures, canpopulation dynamics. Today, integrated pest control forms the be integrated with a view to achieve the ultimate aim offoundation of Integrated Vector Management programs (IVM) combating human disease. Chemical and biological methodsthat take a comprehensive and multi-disciplinary approach to may provide temporary control of vectors but implementation • 924 •
  • 25. of environmental control measures leads to permanent control. form a part of extensive countrywide programmes for controlIn this approach, initial costs may be high and programmes & eradication of diseases and are broadly divided into naturalmay require years for implementation, but authorities at all & synthetic. Natural insecticides can be plant & mineral basedlevels should be advised to include environmental changes whereas Synthetic insecticides can be organic or inorganic.and improvements relating to vector control in all long The organic Insecticides fall into four major groups’ viz.term planning. However, these methods require elaborate Organochlorines, Organophosphates, Carbamates and Syntheticorganization, longer time and liberal finances. Species control pyrethroids. Organochlorine Compounds are contact poisonsand vector control are the two modifications circumscribing the and act on the nervous system, the only member of this groupwider concept of vector control. used in Public Health is DDT. Currently DDT is being used only in North Eastern states of Fig. - 25 : Integrated Vector Management India for Indoor Residual Spray. A deposit of 1 g a.i of DDT/m2 of surface area of walls and ceilings up to a height of 3.5 m in all dwellings applied at 8 weeks’ interval effectively controls majority of the mosquitoes and also other arthropods resting on the treated wall. Organophosphorus Compounds - insects which have become resistant to Organochlorines are still susceptible to the members of this group. Some of the common compounds are Malathion, Temephos, Fenthion, Dichlorovos (DDVP) and Fenitrothion. Malathion is one of the least toxic Organophosphorus compounds. Malathion is a broad spectrum insecticide with efficacy against a large number of pests ranging from mosquitoes, houseflies, cockroaches, bedbugs, lice etc. Malathion (25% WP), under the National Vector Borne Diseases Control Programme is being used as Indoor Residual Spray against mosquitoes in areas where the vectors haveFuture Policy become resistant to DDT. As ULV spray, Malathion has been very widely used during outbreaks of Dengue and JE as anThe aim of future vector control by use of insecticides should anti adult mosquito measure. Temephos (Abate) is the onlybe to reduce the intensity of chemical selection by reducing the insecticide approved for use in potable water (20ml a.i/sqm).frequency and coverage of insecticide sprays in public health Fenthion (Baytex) 82.5% EC is a good mosquito larvicide butprogrammes, minimizing the agricultural use of persistent cannot be used in potable water bodies. It is highly effective aschemicals as far as possible and by supplementing the chemical a larvicide against Culex quinquefasciatus. Dichloro-dimethyl-control methods by other methods whenever feasible. There dichlorvinyl-phosphate (DDVP or Dichlorvos) produces fatalis a need to strengthen existing surveillance methods and insecticidal vapour and can be combined with solid substancesincorporating the benefits of the newer methods like Remote like wax and used as tablets or bricks. It is one of the commonsensing, Geographical Information System, Global Positioning insecticides used for disinfecting aircraft and is also anSystem etc. whenever and wherever, feasible. There is a effective housefly larvicide. Carbamates are derivatives ofcontinued effort to evolve safer alternatives for vector control carbamic acid; some of the compounds in common use arecoupled with intensive research using molecular biology tools Propoxur, Carbaryl and Bendiocarb. Synthetic Pyrethroidsfor production of Genetically Modified Vectors (GMV) to address are broad spectrum, highly potent, have quick knock downthe problems of vector control. action and long residual life. Synthetic pyrethroids are manySummary times more effective & safer than the previously available insecticides and include insecticides like Permethrin, Allethrin,Arthropod control is one of the key strategies in the management Phenothrin, Cypermethrin, Cyfluthrin, Deltamethrin, Bifenthrinof vector borne diseases. This requires a sound knowledge of etc. Deltamethrin, Cyfluthrin are used for bednet treatment &bionomics, insecticide susceptibility & role in arthropod borne routine household pest control activity.disease transmission. The various control options availableare environmental, biological, chemical, personal protective Equipment for vector control can be broadly classified asmeasures, mechanical, physical, genetic & legislative control. ground equipment and equipment used for aerial applications.Environmental control consists of a naturalistic approach with Commonly used for spraying various insecticidal formulationsthe aim of minimizing vector propagation & reducing man- are the hand operated sprayers, power operated sprayers,vector-pathogen contact. Environmental modification consists aerosol dispensers, fog generators and dusters. Residualof transformation that is permanent like drainage, filling Spraying is the application of insecticides to surfaces so that theand velocity alteration. Environmental manipulation aims at insecticide particles remain on the surface in the form, size andproducing temporary conditions unfavourable to the breeding quantity suitable for insects to pick up on contact and sufficientof vectors in their habitats like water salinity changes, stream to exert a lethal effect over a long period. Organochlorine,flushing etc. Organophosphorus, Synthetic pyrethroids and Carbamate compounds can thus be applied on the inside walls of housesChemical control began with the discovery of the insecticidal and also on thick bushes. Before starting a spray operation, thevalue of Dichloro Diphenyl Trichloro ethane (DDT). Insecticides • 925 •
  • 26. equipment must be checked; the average discharge of an 8002 promising control options. Bti 12 AS is used @ 20ml/m2.nozzle is about 750 ml per minute. Spraying in a room should Genetic Control is the” use of any condition or treatment thatcommence from the backside of a door clockwise completing the can reduce the reproductive potential of noxious forms byplain surfaces of walls to the crevices on the walls and inside altering or replacing the hereditary material”.portion of windows etc. The pillars, under surfaces of furniture Personal protective measures to prevent the arthropod vectorsand lastly the ceilings should be taken for spray. Spray is done from biting and feeding on their host can be achieved byfrom roof to floor, using downward motion, to complete one use of mosquito nets, wearing of long trousers, rolled downswath; then stepping sideways and spraying upwards from sleeves of shirts, socks, shoes and anklets (particularly whenfloor to roof. Spray is applied in vertical swaths 52-56 cm wide. going out and in areas heavily infested with arthropods) andSwaths should overlap by 5 cm. use of repellents by application on body surfaces or clothingSpace Spraying is an ideal method for bringing about rapid (are effective in reducing man-vector contact). The commonlycontrol of vectors in emergency or epidemic situations and used repellents are benzyl benzoate, N, N-diethyl-m-tolumidemay also be used for seasonal control of flying insects, pests (DEET), Dibutyl phthalate (DBP), Diethyl phenyl acetamideor vectors. Space sprays are applied mainly as thermal fogs or (DEPA) and Neem oil.cold fogs. Thermal fog is produced by special devices known as The development of resistance, effects on non-target organismsthermal foggers that use heat to break up the chemical into very and damage to the environment can all be minimized withsmall droplets (usually in 5-30 micron diameter range) which selective and judicious use of multi-faceted control tactics.then disperse in the air. The insecticide used in thermal fogs is Integrated Vector Management is a dynamic approach whichdiluted in a carrier liquid, which is usually oil-based. Cold fog requires a broad knowledge of vector biology, ecology andis produced by a special device which breaks up the chemical behaviour on one hand and that of system analysis approachinto microscopic droplets by mechanical means basically with on the other so that a variety of control measures such asa high-pressure pump and an extremely fine nozzle. The spray environmental, chemical, biological, genetic and personaldroplets are generated without any external heat. With cold protective measures can be integrated with a view to achievefogs, the volume of spray is kept to a minimum. Ultra-low- the ultimate aim of combating human disease.volume insecticide formulations are commonly used for suchapplications. The cold fogger may dispense formulations in a Study Exercisesvery concentrated form and generate the droplets (usually in Short Notes : (1) Environmental Management (2) Biologicalthe 5-30 micron diameter range) in a precise manner. However, control (3) Biorational insecticides (4) IRSits ability to penetrate dense foliage or obstacles is not as goodas that of thermal fogging. Cold fogging is sometimes called MCQs & ExercisesUltra Low Volume (ULV) treatment as it allows the utilization 1. Organophosporus insecticides include all exceptof only a very small amount of chemical for coverage of a (a) Temephos (b) Malathion (c) Propoxur (d) Dichlorvoslarge area. Space-spraying formulations are generally oil- 2. Deltamethrin belongs to which group of insecticidesbased. Diesel is used as a carrier for thermal fogging, but (a) Carbamates (b) Synthetic Pyrethroidscreates a thick smoke and oily deposits, which may lead to (c) Organophosphates (d) Organochlorides.public rejection. Insecticides used for fogging are Pyrethrum 3. Which of the following is a chitin synthesis inhibitor :2% Extract, EC, Malathion Tech, Deltamethrin 1.25 ULV. The (a) Imidacloprid (b) Novaluron (c) Fenoxycarblower the concentration of active ingredient, the larger the (d) Cyfluthrin.number of droplets of a given size required to achieve a lethal 4. Maximum amount of pesticide on surface is available fordose. Suppression of vector populations over large areas can be killing pests in this formulation (a) Dusts (b) Granulescarried out using space sprays released from aircraft, especially (c) Wettable powder (d) Liquid formulation.over areas where access with ground equipment is difficult and 5. Hand operated equipment for vector control does notextensive areas need to be treated very rapidly. Area Spraying include : (a) ULV fogging machine (b) Hand sprayeris carried out for treatment of land against mites and ticks and (c) Knapsack sprayer (d) Compression pneumatic sprayeralso as an anti-larval measure over vast water surfaces. 6. Commonest type of equipment used in National Vector Borne Disease Control Programme (a) PowerBiological Control is the manipulation of populations of living operated sprayer (b) Hand sprayer (c) Knapsack sprayerbeneficial organisms in order to reduce the numbers of pests (d) Compression pneumatic sprayeror amount of damage. The biological agents are broadly 7. Insecticide not used for bed net treatment : ( a) Deltamethrinclassified as Predators, Parasites and Pathogens. Predators are (b) Permethrin (c) Cyfluthrin (d) Allethrinoften large, active, and/or conspicuous in their behaviour e.g. 8. Space spraying is used as method of bringing downlarvivorous fishes for the control of mosquitoes like Gambusia rapid control of vector in (a) Emergency (b) Epidemicaffinis. Parasites like Nematodes - Romanomermis culicivorax (c) Seasonal control of flying insects (d) All.and R iyengari have been evaluated and have been found to 9. Which of these is not true for thermal fogginggive variable control of mosquitoes. Fungi Lagenidium and (a) easily visible fog (b) Low conc.of active ingredientCulicinomyces have shown immense potential as mosquito (c) Pyrethrum2% & Malathion tech used (d) Mostly waterlarval control agents and can be exploited for use against diluted formulations used.mosquitoes. Pathogens - Bacillus sphaericus and Bacillusthuringiensis var israelensis which acts via delta endotoxin are • 926 •
  • 27. 10. Predators used in biological control are all except 14) __________________ effect is unique action of Fipronil. (a) Poecelia reticulata (b) Gambusia affinis (c) Bacillus 15) ______________ powder & ______________ tablet is used sphaericus (d) Gaurami for rodent control.11. Match the Following : 16) Average discharge of an 8002 nozzle is ______________ 17) Mechanism of action of Bti is by the action of 1. Pyrethrum (a) Malathion ______________ Answers : (1) c; (2) b; (3) b; (4) c; (5) a; (6) d; (7) d; (8) d; 2. DDT (b) Temephos (9) d; (10) c; (11) 1-c; 2-d; 3-a; 4-b; 5-e;6-h;7-f;8-g;9-j;10-i; 3. Broad spectrum (c) Available as 2% Extract. (12) Paul Muller; (13) Rapid knockdown; (14) Cascade insecticide used in IRS Require 20 times dilution (15) Calcium cyanide & Aluminium phosphide (16) 750ml/ min where resistance to to get 0.1%solution. Has (17) Delta-endotoxin DDT has occurred rapid knockdown action. (d) Used as IRS in the Further Suggested reading 1. WHO. Manual on Environmental management for mosquito control with 4. Available as 50% EC. dose of 1g/m2 of surface special emphasis on malaria vectors. WHO offset Publications. WHO, Used in potable water area of walls & ceilings Geneva, 1982; 66 : 1-238. up to a height of 3.5m. 2. WHO. Environmental management for vector control. Third report of the WHO Expert Committee on Vector Biology and Control. Technical Report 5. Mosquito larvicide, Series. WHO, Geneva, 1980; 649 : 1-75. 3. Sharma VP Environmental management in malaria control in India. In : . cannot be used in potable Targett GAT, editors. Malaria - waiting for the vaccine. John Wiley publishers, water bodies, highly (e) Fenthion USA 1991 : 49- 66. effective against Culex 4. Rozendaal Jan A. Vector control : Methods for use by individuals and quinquefasciatus communities. Geneva : World Health Organization, 1997. 5. Curtis CF, editor. Control of Disease Vectors in the Community. 1st ed. London: 6. Effective housefly Wolfe, 1991. larvicide, available as 76%EC (f) Propoxur 6. Prevention &management of insecticide resistance in vectors and pests of public health importance. Manual by Insecticide Resistance Action & in aerosol formulations. Committee (IRAC). 7. Flushing out effect makes (g) Available as 2.5%SC, 7. WHO. Chemical Methods for the control of Arthropod Vectors and Pests of Public Health Importance. Geneva : World Health Organization, 1984. it useful for cockroach 2.5%WP & 1.25 ULV 8. World Health Organization. Safe use of Pesticides. Tech Rep Ser no 513. &bed bug control in space sprays WHO, Geneva 1973. 9. WHO. Implementation of global malaria control strategy. Technical Report 8. Deltamethrin (h) DDVP Series. WHO, Geneva, 1993; 839 : 1-57. (i) Available as 2.15% gel 10. WHO. A global strategy for malaria control. Geneva : World Health 9. Cannot be used in potable Organization, 1993. for use against cockroaches water , available as 12AS 11. Matthews GA. Pesticide application methods. 3rd ed. Blackwell Science, & bait against houseflies 2002. 12. Reiter P Nathan MB. Guidelines for assessing the efficacy of insecticidal , 10. Imidacloprid (j) Bti space spray for control of the dengue vector Aedes aegypti. Geneva, World Health Organization (document WHO/CDS/CPE/PVC/2001.1), 2001.Fill in the Blanks : 13. Najera J, Zaim M. Malaria vector control : decision making criteria and procedures for judicious use of insecticides. Geneva, World Health12) Residual insecticidal property of DDT was discovered Organization (document WHO/CDS/WHOPES/2002.5), 2002. by __________________ 14. WHO. Equipment for vector control, 3rd ed. Geneva, World Health13) Mechanism of action of Pyrethrum __________________ Organization, 1990. However, the most abundant and widely distributed is the 156 Housefly Housefly. Classification and Distribution Rina Tilak The houseflies have a world wide distribution with about 1700 genera under family Muscidae, order Diptera to which theHouseflies live in close association with man. Despite the best medically important flies - houseflies and stable flies belong.and most extensive efforts taken to control it, housefly control There are 70 species of flies in genus Musca, of which Muscahas remained a challenge. The important genera include domestica (common housefly) and Musca sorbens (bazaarMusca, Fannia and the biting flies, Stomoxys, Sarcophaga and fly) are abundantly encountered in tropical and subtropicalthe various blowflies viz. Chrysomya, Calliphora and Lucilia. countries. • 927 •
  • 28. Morphology Houseflies breed in decaying organic matter of animal or plantAdult houseflies are 6-9 mm in length, greyish in colour with origin. The eggs are pearly white, oval in shape and measure4 distinct longitudinal black stripes on the thorax. The head about 1 mm in length. They are laid in cracks & crevices inbears a pair of compound eyes which are close together in moist manure heaps or any decaying animal or vegetablemales but are widely separated in females. The mouth parts, matter. A female fly may lay 300 to 900 or more eggs in 5 tocollectively known as the proboscis are capable of considerable 6 batches during her lifetime. In summer, the eggs hatch afterextension and retraction and are adapted for lapping-sponging. 8-12 h, whereas in winter it may take 2 to 3 days. There areThe antennae generally remain hidden in the antennal groove three larval stages or instars in the life of a fly. The larvaeon the head. The thorax bears four narrow black stripes, a are photophobic and thus are found in the deeper layers of thepair of clear transparent wings and a pair of halteres (knob manure. After 3-5 days, the third stage larva moves from deeplike structure behind the wing), three pairs of legs - each moist burrows to the neighbouring dry soil and contracts toterminating in five segments of tarsus; the last segment bears form a dark brown barrel shaped pupa about 6 mm in length.a pair of claws and pair of pad-like ‘pulvilli’ provided with a The pupa neither feeds nor grows. Within 2-5 days, the adultlarge number of glandular hairs. These glandular hairs secrete fly emerges out of the pupal case. Under favourable conditionsa substance which keeps the pads wet and sticky and enables of temperature and food supply, the whole life cycle from eggthe flies to cling to vertical and smooth surfaces. The abdomen to adult may be completed in about less than a week’s time.is short, broadly oval with five visible segments (Fig. - 1). During winter it may take as many as 20 to 22 days. The length of life is usually 2-3 weeks but in cooler conditions it may be as Fig. - 1 : Musca domestica long as three months. Bionomics The housefly has a remarkable capacity to reproduce. It is estimated that at an average of 7 day’s developmental cycle for each generation, one female housefly, laying about 120 eggs, could produce a progeny of 5,598,72000,000 adult flies by the end of 5 months in summer. However, nature does not allow this as a large number of eggs, larvae and pupae are lost due to desiccation, starvation, predators and adverse climatic conditions. A high percentage of flies remain near the breeding places. Depending on the prevailing wind and availability of food, some of them may migrate up to 20 km from breeding places (however most stay within 1-2 km of the larval habitat if sufficient food is available). High temperature is lethal to larvae and so the heat generated in tightly packed manureLife History heap quickly kills them. The adult houseflies are attracted toThe life cycle of housefly undergoes complete metamorphosis light. The housefly is omnivorous and a voracious feeder; it iswith egg, larva (maggot), pupa and adult stages (Fig 2). particularly partial to faecal matter, sputum, discharges from wounds and open sores. It is also easily attracted to sugars, Fig 2 : House fly - Life cycle milk and other articles of food meant for human consumption. The solid or semi-solid foods are softened by extrusion of a vomit drop and then sucked up. Well fed fly defecates every 5 min, particularly while feeding, and vomits every 2-3 minutes. Water is an essential part of a fly’s diet and flies do not ordinarily live more than 48 hours without access to it. 2-5 days 3-6 days Pupa Ecology of Adult Flies An understanding of the ecology of flies is essential for effective management of houseflies. Flies are mainly active during daytime when they feed and mate. They are generally Larva Adult found resting indoors on floors, on the ground and walls at less than 5 feet from the ground; whereas outdoors they rest on fences, walls, steps, pit latrines, clothes lines, grasses, weeds Egg and garbage cans. At night, flies rest above 5 feet height on walls, on hanging wires and vertically suspended articles and 8-24 hrs ceilings, usually close to their daytime food sources. 2-7 days Vector Potential Immediately after visiting a dirty place, the fly may rest on any foodstuff or drink meant for human consumption or an exposed part of body e.g. mouth, eyes or a wound, and deposit the • 928 •
  • 29. disease producing organisms. The housefly is thus a mechanical water containers/ troughs or within reach of animals or pets.carrier of the causative organisms of diarrhoeas, dysenteries, Curtains treated with Synthetic pyrethroids will be of additionalgastroenteritis, cholera, enteric group of fevers, intestinal benefit.worms, poliomyelitis, viral hepatitis A, other entero- viruses, (iv) Larvicides : Insecticides such as DDVP (2%), Fenthion (4%)trachoma, conjunctivitis, anthrax, yaws and tuberculosis. At have been used as larvicides to control fly breeding but thetimes, the housefly may cause conditions known as internal use of larvicides may favour the development of resistance,and external myiasis, in which the flies breed in sloughing the choice should therefore be made carefully. Insecticideswound, intestinal contents and suppurating cavities. like Dimilin (IGR) may be used to retard development ofFly Control resistance. Larvicides should be applied at a rate sufficient to(a) Environmental Control : The best method of control of wet the upper 10-15 cm of the breeding medium thoroughlyhouseflies is to eliminate their breeding places and to maintain i.e. 0.5 - 5 l/m2.a high standard of environmental sanitation, especially byproper disposal of human and animal excreta, swill, garbage Box - 1 : Newer Insecticides Against Housefliesand all other decaying organic rubbish, offal and carcasses. Formu- Area to be Insecticide DilutionAccess of flies to faeces should be prevented by fly proofing lation sprayedthe latrines and latrine pans and prompt removal of faeces. 10 ml +Their access to food is prevented by fly-proofing cook houses Cyphenothrin 5%EC 990 ml 500 ml/sq mand messing blocks and by use of fly-proof cupboards and of watercontainers. The doors of all entrances and windows shouldopen outwards and preferably should have vacuum levers 2.5% 8 g in 1 Diflubenzuron 500 ml/sq mespecially in cookhouses. Constant vigilance is necessary to WP litre waterdestroy all flies that gain entrance, otherwise the fly-proofed Diflubenzuron 5% G As it is 50 g/sq mrooms become large fly-traps. In pantries and mess rooms, Imidaclopridfly-proof cupboards for food storage and wire gauze, weighted 0.5% As it is 5 g / bait station baitwith beads afford protection to food in jugs or bowls but theirrepair and cleanliness requires constant supervision. When Moisten and keep Propoxur bait 2% As it isthe table is being laid, cups should be inverted in saucers and in bait stationsbowls should be kept either upside down or under cover whennot in use. (v) Paints : The concept of using insecticidal paint for housefly(b) Insecticidal Control (Box - 1) is catching up. Imidacloprid baits wetted with water may be used as paint on housefly resting places.(i) Space Spray : For immediate destruction of flies andespecially for prevention of fly borne diseases, pyrethrum (vi) Residual Spray : The housefly has developed resistance(0.1%) spray is useful, mainly in cook houses and dining rooms to most of the Organochlorine as well as Organophosphorusbefore meal times and in canteens. Certain combinations of and Carbamate group of insecticides routinely used in publicspace sprays containing Pyrethrum or Synthetic pyrethroids health. Residual sprays are ideally not recommended for flyand/or Organophosphorus/Carbamate compounds are available control.commercially. ULV spray in large areas may also prove effective (c) Mechanical Controlin controlling houseflies. (i) Fly Traps : Various types of fly traps such as the cage trap(ii) Baits : Propoxur baits have been in use since long for fly and the kerosene tin trap were used in the past with fairly goodcontrol. Recent introduction in this concept is Imidacloprid results. These are no longer in use because of the availabilitybaits containing Imidacloprid as the toxicant with Pheromone of more potent and convenient methods. Newer mechanical fly- Muscalure, which helps in attracting the flies to the bait. This catching devices have been developed which have bags withbait has been found to be effective for use in areas with low to attractants inside, which attract the houseflies and on entrymoderate fly infestation. However, while using these baits in inside the bag, they get trapped and eventually are killed.cookhouses/ dining areas, care should be taken that they are (ii) Swatting : It is used in situations where infestation is sonot placed close to cooking or serving place. low that routine fly control measures are either not indicated(iii) Cord and Ribbons : During the night, houseflies prefer or feasible. However, it is important to remember that flyto rest on strings and hanging wires or any object; this fact population of a cook house or dining room cannot be greatlyis utilized for killing them by use of insecticide treated cords reduced by persistent swatting. A good swat is the one, whichand strips which are hung from ceilings in kitchens, dining is resistant enough to affect a rapid hit. The flaps should behalls, store rooms, dairy farms and poultry houses to provide perforated and washable.effective control during the fly season. Dark coloured material (iii) Fly Paper : Commercially available fly papers may be usedis preferred for treatment @ 1m cord or strip for each square or alternately sticky fly papers (Fig. - 3) can be prepared bymetre of floor space. The period of effectiveness ranges from mixing 8 parts of powdered resin and 5 parts by weight of crude1 to 6 months. For this any insecticide with high vapour castor oil and heating the same in a water bath while stirringpressure and quick knock down effect should be used. These constantly. The paste mixture is spread on glazed paper. Thetreated materials should not be hung over food containers, latter can be prepared by coating an ordinary paper with a hot • 929 •
  • 30. solution of 1 g of glue in 3ml of water and allowing it to dry. of fevers, intestinal worms, poliomyelitis, viral hepatitis A,The fly papers do not give lasting results and hence are not other entero- viruses, trachoma, conjunctivitis, anthrax, yawsmuch in use for control purpose. They are however considered and tuberculosis.an effective method for monitoring fly density. The best control of houseflies is to eliminate their breeding places and to maintain a high standard of environmental Fig. - 3 : Fly paper sanitation, especially by proper disposal of human and animal excreta. Access of flies to faeces should be prevented by fly proofing the latrines and latrine pans and prompt removal of faeces. Their access to food is prevented by fly-proofing cook houses and messing blocks and by use of fly-proof cupboards and containers. The doors of all entrances and windows should open outwards and preferably should have vacuum levers. Insecticidal Control : Space Spray of pyrethrum (0.1%) useful for immediate destruction of flies & for prevention of fly borne diseases. Propoxur baits have been in use since long for fly control. Recent introduction is Imidacloprid baits. Use of insecticide treated cords and strips provide effective control during the fly season. Other useful insecticides are DDVP (2%),(d) Physical Control : Use of light traps (electrocutors) is very Fenthion (4%), Dimilin etc. Mechanical fly catching devicesuseful in the dining areas & other public eating places. The have been developed which have bags with attractants inside,light traps should be placed away from dining tables & food. which attract the houseflies and on entry inside the bag, they get trapped and eventually are killed. Swatting is used inSummary situations where infestation is so low that routine fly controlHouseflies live in close association with man. The most measures are either not indicated or feasible. Commerciallyabundant and widely distributed is the Housefly - Musca available fly papers may be used or alternately sticky fly papersdomestica. Adult houseflies are 6-9 mm in length, greyish in can be prepared. Use of light traps (electrocutors) is very usefulcolour with 4 distinct longitudinal black stripes on the thorax. in the dining areas & other public eating places, however, theyThe head bears a pair of compound eyes. The thorax bears a should be placed away from dining tables & food.pair of clear transparent wings, three pairs of legs - the lastsegment of the tarsus bears a pair of claws and a pair of Study Exercisespad-like ‘pulvilli’ provided with a large number of glandular MCQshairs. These secrete a substance which keeps the pads wet 1) Housefly transmits all except (a) Poliomyelitisand sticky for clinging to vertical and smooth surfaces. The (b) Hepatitis B (c) Tuberculosis (d) Intestinal worms.life cycle of housefly undergoes complete metamorphosis 2) Environmental control measures for housefly control dowith egg, larva, pupa and adult stages. Houseflies breed in not include (a) Fly proofing (b) Pyrethrum spray (c) Properdecaying organic matter of animal or plant origin, eggs are laid garbage disposal (d) Vacuum levers in doors.in cracks & crevices in moist manure heaps or any decaying 3) Anti adult control measure is (a) Fenthion (b) DDVPanimal or vegetable matter. The larvae are photophobic and (c) Dimilin (d) Imidacloprid bait.thus, are found in the deeper layers of the manure. After 3-5 Fill in the Blanksdays, the third stage larva moves from deep moist burrows to 4) Size of a housefly is ______________the neighbouring dry soil and contracts to form a dark brown 5) ______________ secrete a substance which keeps pads wetbarrel shaped pupa. Within 2-5 days, the adult fly emerges out & sticky for clinging to vertical &smooth surfaces.of the pupal case. Under favourable conditions of temperature 6) Larvae of housefly are ______________and food supply, the whole life cycle from egg to adult may be Answers : (1) b; (2) b; (3) d; (4) 6-9mm; (5) Pulvilli;completed in about less than a week’s time. During winter it (6) Photophobic.may take as many as 20 to 22 days.The housefly has a remarkable capacity to reproduce. High Further Suggested Readingtemperature is lethal to larvae and so the heat generated in 1. Keiding J. The housefly biology and control. Training and information guide. Geneva : World Health Organization, 1986.tightly packed manure heap quickly kills them. The adult 2. Zurek L, Denning SS, Schal C, Watson DW. Vector competence of Muscahouseflies are attracted to light. The housefly is omnivorous domestica (Diptera : Muscidae) for Yersinia pseudotuberculosis. J Medand a voracious feeder. It is particularly partial to faecal Entomol 2001; 38 : 333-5. 3. Fotedar R. Vector potential of houseflies (Musca domestica) in thematter, sputum, discharges from wounds and open sores. The transmission of Vibrio cholerae in India. Acta Trop 2001; 78 : 31-4.housefly is a mechanical carrier of the causative organisms of 4. Nayduch D, Noblet GP Stutzenberger FJ. Vector potential of houseflies for the ,diarrhoeas, dysenteries, gastroenteritis, cholera, enteric group bacterium Aeromonas caviae. Med Vet Entomol 2002; 16 : 193-8. • 930 •
  • 31. stages of egg, larva, pupa and adult. Water is required for egg 157 Mosquitoes laying with variations existing among genera and species for the type of water desired by them. The number of eggs laid at each oviposition varies between 50 and 150. Anophelines Rina Tilak prefer to lay their eggs singly in clean water collections and have lateral floats; Culex sp prefers dirty/ polluted water andMosquitoes qualify to be rated as one of the most important the eggs are deposited as raft; Aedes sp prefers to lay eggsvectors, the world over, from amongst the numerous species singly on some substratum/ debris in containers (natural orof blood sucking arthropods, due to the sheer magnitude of artificial), whereas Mansonia sp breeds in water bodies withmorbidity and mortality caused by them. The mosquitoes belong aquatic vegetation namely Pistia and lay their eggs on theto phylum Arthropoda, class Insecta, order Diptera and family under surface of the leaves in star shaped clusters. The eggsCulicidae. The family Culicidae is divided into sub-families hatch into larvae in one to two days, but in cold weather, theCulicinae, the Chaoborinae and the Dixinae. Of these, only the hatching may be delayed. Mosquito larvae feed voraciouslysub-family Culicinae, which comprises all the true mosquitoes, on micro-organisms, water algae or other organic matter andis of medical importance. Amongst the mosquito genera, only breathe through spiracles. Larvae pass through four stages orAnopheles, Culex, Aedes and Mansonia are of importance in “instars’ in five days depending on the species, the temperatureIndia. The mosquitoes are further classified as ‘Anophelines’, of the water and availability of food supply. In Anophelines, thewhich comprises only one important genera - Anopheles and larvae rests parallel to the surface and have palmate hair on‘Culicines’ comprising three important genera viz. Culex, Aedes the dorsal surface of the abdomen and do not possess siphonand Mansonia. tube, whereas in case of Culicines, the larvae rest at an angleDistribution with the head downwards and possess a single siphon tube. AtMosquitoes have a worldwide distribution, being found in the the end of the fourth instar, the fully grown larva casts its skintropics, temperate zones and also in the arctic circles. They and becomes a comma shaped ‘pupa’, which is a motile buthave even been found breeding in underground tunnels, deep non-feeding stage and has two respiratory trumpets originatingmines and at altitudes as high as 4000 m above sea level. from the cephalothoracic area. During this stage, it undergoes transformation to the adult usually within 1-2 days. The adultMorphology mosquito wriggles out of the pupal skin through a ‘T’ shapedMosquitoes are about a centimetre long and greyish black slit and balances itself on the water surface or some near byin colour. The division of the body into the head, thorax floating object until its wings are dry and then flies off. Theand abdomen is sharply defined. The head bears two large total duration of the life cycle varies between seven days to onecompound eyes, a pair of antennae and the mouthparts which month. The life span of adult mosquitoes is up to a maximumare collectively called ‘proboscis’. The mandibles and maxillae of 6 months in the temperate zones, but in the tropics theyof only the female are developed for cutting the human skin seldom survive for more than a month.and therefore only the female mosquitoes can suck blood and Bionomicstransmit diseases. The females of all the medically important mosquitoes areSexual dimorphism is clearly seen in mosquitoes; males can be normally bloodsuckers, as they require a blood meal foridentified by their antennae, which are densely haired and look maturation of eggs. Females are fertilized during swarminglike moustache, whereas, in females the antennae is sparsely (nuptial dance) at dusk. The source of the blood meal varieshaired. with the species. Those feeding on human blood are calledThe palps are also helpful in identification of males and females anthropophilic and those feeding on animals are calledof Anophelines and Culicines; In Anopheles male, the palpi are zoophilic. They are attracted by the body odours, carbonlong and club shaped at the termination; in the females, they dioxide and heat emitted from animals or humans. Majorityare as long as proboscis and are straight. In Culicines, the of species are nocturnal in their feeding habits, while othersmale palpi are long and tapering and deflected out, whereas feed indiscriminately by day or night. Some are outdoor bitersin females, the palpi are much shorter than proboscis and (exophagous) and some are indoor biters (endophagous). Afterbudlike. blood meal, female goes in search of a quiet place indoorsThe thorax bears a pair of wings and three pairs of legs. The (endophilic) or outdoors (exophilic) to rest for a variable period,thorax of Culicines is humped in all the three genera, giving them usually 2 days and matures her eggs. When the eggs are fullya hunchback appearance while resting; whereas, Anophelines matured, she goes in search of water collection for ovipositionrest with their head, thorax and abdomen in the same line and (act of laying eggs). Male mosquitoes feed on flower-nectar andforming an angle of 45° with the surface, with the exception of plant-juices and do not survive long after fertilizing the femaleAnopheles culicifacies which rests like the Culicines i.e. with mosquito.the body parallel to the surface. The abdomen of mosquitoes Genus Anophelesconsists of 10 segments of which 7 or 8 are clearly marked Members of this genus have 58 species in India. Females ofout and the terminal ones form the male and female external only 9 species of Anopheline mosquitoes are the vectors ofgenitalia. human Plasmodia in India (Fig. - 1). In certain parts of theLife History world, some species of Anopheline mosquitoes transmitMosquitoes undergo complete metamorphosis through the Wuchereria bancrofti and Brugia malayi infections as well. • 931 •
  • 32. All important vector species are preferentially anthropophilic. Fig. - 2 : Culex MosquitoThe time of feeding is also variable; some species prefer duskfor their blood meals, others late night while still others selectearly morning. Knowledge of the habits is useful in designingcontrol measures. An identification key for common Anophelines Egg Pupaof India is presented at the end of the section. Detailedentomological techniques are given in the WHO manual anda pictorial identification key has also been published by Daset al. Larva Fig. - 1 : Anopheles Mosquito Head of male Head of female Resting position Egg Larva Lateral floats Pupa damp surfaces on stagnant water. During the pre-monsoon period, the breeding is restricted to water collections meant for domestic use. Communities or sections of the cities with water scarcity, which leads to water storage practices, are mostly harassed by Ae aegypti. In the shore areas, barges and Head of male Head of female Resting pose country crafts provide ample place for Aedes breeding and constitute a permanent source of Aedes infiltration in the shore establishments and cities. They are well adapted for breeding in small collections of water in a wide variety of natural and artificial containers such as masonry tanks, earthenware pots,Genus Culex small and large tins, barrel drums, coconut shells, stored orMembers of this genus are found in temperate and tropical discarded motor car tyres, junk and hardware, flower pots, firezones throughout the world. There are 240 Indian species in buckets, depressions in tree trunks, leaf axils etc. They maythis Genus. Adult mosquitoes of this genus are generally dull breed in tree holes if these are situated within about 20 metresin colour and inconspicuous due to unspotted wings (Fig. - 2). of human habitat.Their breeding sites vary from clear water, such as wells and The eggs after maturing may remain viable for considerablesprings, to collections of muddy, brackish or polluted water; periods even after drying-up of the breeding sites, and hatchbut unlike Anopheline mosquitoes, these mosquitoes generally out during rains. Such surviving eggs rapidly build up theprefer stagnant and muddy pools. C quinquefasciatus is the adult mosquito population, once it starts raining. Theircommon house mosquito and is prevalent universally; it bites capacity to complete life cycle indoors enables them to breed inat night and is the most important vector of Filariasis caused urban areas throughout the year, irrespective of the prevailingby Wuchereria bancrofti. external climate.Genus Aedes Aedes mosquitoes are day biters with dawn and dusk as peakSome members of the genus Aedes have almost worldwide biting time. They may feed indoors or outdoors and rest neardistribution while others have restricted habitats. The chief the breeding places in dark, shady corners outdoors, whereasspecies in India are Aedes aegypti, Ae albopictus and Ae vittatus. indoors they rest behind cupboards, hanging clothes, insideThey are black or dense brown and medium sized mosquitoes shoes, umbrellas, below the furniture and in containerswith silvery white scales forming patterns on the thorax, bands providing breeding sites. Aedes aegypti prefers to breed inon the legs and rings around each abdominal segment. artificial containers, whereas Aedes albopictus prefers naturalThese mosquitoes are mostly anthropophilic and are adapted containers.to domestic or semi-domestic environments. These are Aedes mosquitoes are the vectors of urban and rural yellowcontainer breeders. The cigar shaped eggs are laid singly on fever (not in India), dengue, dengue haemorrhagic fever • 932 •
  • 33. and chikungunya. Ae niveus has been reported as vector of anchored to the under surface of the leaves of aquatic plantsW bancrofti (diurnally sub periodic) infection in Nicobar such as Pistia, Lemna, Eichhornia and Salvinia. On hatchingIslands. Ae aegypti and Ae albopictus, the two important vector out, the larvae obtain oxygen from the plant cells through theirspecies can be easily distinguished by their thoracic pattern. modified siphon tubes by attaching themselves to the rootletsAe aegypti has sickle or lyre shaped pattern on the thorax, of these plants. The pupae are similarly attached to the plantwhereas Ae albopictus has a single central mark present on the stems by the modified breathing trumpets. When maturedthorax (Fig 3). they detach themselves and come to the water surface. They are persistent biters, particularly during darkness. Mansonia Fig. - 3 : Aedes species identification mosquitoes are the vectors of B malayi infection of filariasis in several pockets in rural areas of Kerala, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, Assam and West Bengal. Fig. - 4 : Mansonia adult with wing depicting typical salt & pepper appearance Mansonia adult Mansonia wing Aedes albopictus Aedes aegyptiGenus Mansonia (Fig 4)This has wide distribution in tropical countries. In India,Mansonia annulifera, M uniformis and M indiana are theprevalent species in Kerala. The adult mosquitoes are robust andyellowish brown. The wings are covered with flat, broad scales, Some of the important differences between Anopheline andwhich give the wings a speckled appearance as if sprinkled Culicine mosquitoes are shown in Table - 1.with mixed salt and pepper. The female lays eggs in cluster Table - 1 : Important differences in Anopheline and Culicine mosquitoes Stage Anopheline Culicine ●● Boat shaped ●● Elongated ●● Laid singly ●● Aggregation occurs into rafts of hundreds of eggs in Culex Egg ●● Possess lateral floats ●● Aedes eggs are laid singly ●● Mansonia eggs are laid on under surface of leaves of aquatic plants in star shaped clusters ●● No siphon tube but only apertures on 8th ●● Single siphon tube on 8th abdominal segment abdominal segment - In Culex, siphon tube is long and narrow ●● Larvae rest parallel to the surface of - In Aedes, it is short and broad water Larva ●● Swim with swift wriggling movements - In Mansonia, larvae are attached through siphon tube to ●● Palmate hairs for floatation arranged in roots of aquatic plants pairs on all abdominal segments ●● Larvae rest at an angle to surface ●● Swim with slow snail or worm like movements ●● No palmate hairs for floatation ●● Pupa is comma shaped ●● Pupa is comma shaped Pupa ●● In Anophelines, respiratory trumpets are ●● In Culicines, respiratory trumpets are longer, slender and short stumpy and funnel shaped trumpet shaped ●● Wings usually spotted ●● Wings usually not spotted ●● Rests at an angle to surface, with the ●● Rests parallel to the surface exception of A culicifacies ●● Thorax is humped Adult ●● In the males, palpi are long and club shaped ●● In the males, palpi long and tapering and deflected out; in at the termination; in females, they are as females, palpi are much shorter than proboscis and budlike long as proboscis and are straight • 933 •
  • 34. Vectors of Malaria not known. Certain new species are emerging as secondaryThere are 58 species of Anopheline mosquitoes in India but vectors in different parts of the country. The Vectorial capacityonly 9 are incriminated as vectors and another 5 species (C) can be expressed as a mathematical expression to measurehave been found to be of local importance in transmission of vector efficiency and assess risk and impact of interventionsmalaria. In Northern and Peninsular India, the main vectors as follows :are A culicifacies, A stephensi and A fluviatilis, while the ma2pnlocal vectors are A sundaicus, A annularis and A varuna. In C= (-loge p)Eastern India, the main vectors are A dirus, A sundaicus, Aphilippinensis, A minimus, and A maculatus. In Andaman and where :Nicobar Islands, the main vector is A sundaicus while the new m = density of vectors in relation to manvectors are A dirus, A maculatus and A tesselatus. A detailedlist of these vectors is presented in Table - 2. a = number of blood meals taken on man per vector per dayThe following characteristics of vector mosquitoes play an p = proportion of vectors surviving per dayimportant role in the epidemiology of malaria. n = incubation period in the vector (days) - 8 days(a) Breeding Habits : The breeding habits of mosquitoes when they survive (1/-logep) days.show a lot of variation and hence vector mosquitoes tend to be Theoretically, incidence of infection rises when C>1, incidenceconfined to certain geographical areas only. A few examples are falls when C<1.as shown in Box - 1. (c) Density : For effective transmission of malaria in a locality, the mosquito vector must attain and maintain a certain density. Box - 1 : Breeding Habits of Vectors This is called critical density and it varies from one mosquito Slow moving water, seepages, terraced A fluviatilis to another and also under different environmental conditions. rice fields A culicifacies needs a very high density for transmission of Brackish waters A sundaicus malaria, while philippinensis, dirus and fluviatilis need much lower critical density. Wells, cisterns and over head tanks A stephensi (d) Longevity : A mosquito, after an infective blood meal, must Tanks, pools, burrow pits and ditches A philippinensis, live for at least 10 days to complete the development of malaria A annularis parasites. Therefore aim in malaria control programme is to Forest pools, streams and slit trenches A dirus reduce the life span of mosquitoes to less than 10 days. (e) Tropism : Some mosquitoes like A fluviatilis prefer human(b) Vectorial Capacity : Only certain species act as vectors; blood and are called anthropophilic. Others like A culicifaciesmoreover, within the known vector species, some are more preferably feed on animal blood and are called zoophilic. Thisefficient while some are less. The exact reasons for this are preferential feeding habit is called tropism. Table - 2 : Malaria Vectors of India and Vectors of local importance S No. Name of Species Role in transmission 1 A stephensi Primary urban vector in most of India except North-East and Rajasthan 2 A culicifacies Primary rural vector all over India except North-East 3 A fluviatilis Primary rural vector in foothill areas of the country 4 A minimus Primary vector in North Eastern regions, West Bengal 5 A phillippinensis Primary vector in rice field ecosystem of North Eastern regions 6 A dirus Primary vector in regions of evergreen forests in the North East 7 A sundaicus Primary vector in Andaman & Nicobar Islands 8 A varuna Eastern ghats (Andhra Pradesh), Singbhum hills (Bihar) & Kerala 9 A annularis Secondary vector in rice field ecosystem in Uttar Pradesh and coastal areas of Orissa Vectors of local importance 1 A aconitus Orissa, Assam 2 A jeyporiensis (var In certain localities in Kerala, Karnataka and Assam candidiensis) 3 A maculatus In certain localities in Assam & Meghalaya 4 A tesselatus Lakshadweep Islands (on epidemiological grounds) 5 A subpictus In Madhya Pradesh • 934 •
  • 35. (f) Biting Behaviour : Some vector mosquitoes bite at or soon Fig. - 5 : Identification of mosquitoafter dusk, others either during late night or early hours of themorning. However, some species may be active at two differentperiods during the same night. Antenna Proboscis(g) Resting Habits : A female mosquito after a blood meal FORE LEGrests either indoors (endophilic) or outdoors (exophilic) for Palpmaturation of its eggs. The common resting places are eitherhuman dwellings, cattle sheds or mixed dwellings. HEAD Eye(h) Flight Range : The range of flight and dispersion variesfrom one vector to another. Some have a short flight range e.g. Scutum WINGflight range for A dirus, A annularis and A fluviatilis is upto 1 THORAX HALTER Cellskm distance; whereas A culicifacies and A stephensi fly up to 2 Veins Scutellumkm and A sundaicus may fly even up to 8 or 10 km.(j) Resistance to Insecticides : When a vector mosquito in a 1 2locality becomes resistant to a particular insecticide, use of an 3 Fringealternative insecticide is recommended. 4 FemurVectors of Filariasis ABDOMEN 5 6(a) Culex quinquefasciatus : This species is the main vector of Tibia 7bancroftian filariasis in India. It preferentially breeds in dirty 8water collections such as in drains, cesspools, soakwells andseptic tanks. When denied such opportunities, it can also breed MID-LEGin clean water. Cercus 1(b) Mansonoides : Mansonoides species are the vectors of TaB malayi infection in India. In Kerala, M. annulifera and M. rsu 2 suniformis are the major vector species. These mosquitoes are 3 Clawassociated with aquatic plants like Pistia stratiotes, Eichhornia 4 5speciosa and Salvinia auriculata. HIND-LEG(c) Aedes niveus : This species has been incriminated as avector of diurnally subperiodic form of Bancroftian filariasis inNicobar group of islands. Identification of Male & Female Mosquito : The mosquito(d) Other Species : In India, Anopheline mosquitoes have not sexes can be identified by their antennae. It’s bushy in malesbeen found to play any significant role in the transmission of and not so bushy in females (Fig. - 6).any type of filarial infection unlike in some other parts of theworld. Fig. - 6 : Identification of Male & Female MosquitoMosquito SurveillanceIn places which are endemic for mosquito borne diseasesor outbreak prone, it is deemed mandatory that mosquitosurveillance system be established. The aim of the surveillanceshould be to inform about changes in density and majorcharacteristics of vectors, to forecast an impending outbreakand to recommend appropriate strategies for mosquito controlwhich would prevent outbreak.Steps for Establishing Mosquito Surveillance SystemStep 1 : Acquaint yourself with basics of mosquito identificationboth larval and adult mosquitoes up to genera level (Culex,Anopheles and Aedes) and mosquito bionomics.Adult Identification of Anopheles, Culex and Aedes : If the wingsIdentification of mosquito : Mosquitoes are identified from are spotted, it is anopheline vector species; whereas, if the legsother such flies by the presence of forward projecting mouthparts are having silvery stripes against dark black legs it is Aedesor proboscis, wing veins (veins 2, 4 and 5 are branched) and a and if there are no spots on the wings or stripes or legs, it isfringe of scales along the posterior margin of wings (Fig. - 5). Culex adult. The length and shape of terminal area of palpi can also be used for discriminating, as explained in Table - 1 earlier. • 935 •
  • 36. Larvae : If the larvae have siphon tube at its tail end, it belongs located close to the breeding places, discarded bathrooms,to Culicine group and could be Culex or Aedes. For this reason, abandoned buildings are considered ideal; for room selection,the larvae of Culicines are suspended upwards down, at an the room which has fewer openings is selected.angle with the water surface. If the siphon tube is long and Step 6 - Conduct Fortnightly Surveys : Conduct surveys in thenarrow, it is Culex species, whereas short and broad siphon fixed and random stations and record your data in the formattube indicates it is Aedes. It is also important to remember that given in Appendix ‘A and ‘B’ at the end of this chapter. ’Aedes is essentially a container breeder and will be found only Larval Sampling Procedure : The mosquito larval samplingin artificial or natural containers. The Culicine larvae float at should be done by standard larval ladles. The method is asan angle to the water surface as shown in Fig. - 7. follows : Fig. - 7 : Culicine Larva Dip the ladle sideways : A minimum of five dips may be taken for calculation of larval density (Fig. - 9). Fig. - 9 : Larval SamplingAnopheles in contrast does not have siphon tube and floatsparallel to the water surface of water as shown in Fig. - 8. Transfer the larvae in enamel bowl : count the total number of larvae in the bowl after five dips. Fig. - 8 : Anopheline Larva Calculate larval density : For example : ●● Total no. of dips taken-5 ●● Total number of larvae counted -50 ●● Larval density (Total no. of larvae/ no. of dips)-50/5 = 10 Other larval sampling procedures like larval nets (when the water body has vegetation) or well nets (when mosquito breeding is noticed in wells) may be used in specific situations. The density is calculated in the same way and given as larvae/ larval net or well net. Adult Sampling Procedure Aspirators / Suction tube : This is the most common method of sampling adult mosquitoes (Fig. - 10). It is normally undertaken in the mornings. Before using suction tube ensureStep 2 - Sector Allocation and Mapping : Once armed with that muslin cloth or gauge piece is placed between the glassthe basic information, start by dividing the entire area of your tube and the rubber tubing to prevent mosquitoes being suckedresponsibility into four or five sectors and make a map of the inside your mouth.sector. Each sector should be covered every fortnight or at leastonce a month for surveillance. Fig. - 10 : Aspirator / Suction TubeStep 3 - Conduct a Preliminary Survey : First a baseline survey(larval and adult) is conducted to determine the prevalence,abundance and distribution of the vector species.Step 4 - Data Compilation and Preparation of Spot Map : Thedata collected in preliminary survey is compiled and analyzedto determine the above mentioned variables and a spot map isprepared with clearly marked out areas where density is high,medium or low or where potential of breeding exists.Step 5 - Establish Monitoring / Catching Stations : In each ofthe four or five sectors, establish four fixed stations (minimumtwo if manpower is less), with preferably two from the highdensity and two from the medium density spots and an equal ●● With the aid of a torch look for resting mosquitoes on thenumber of random stations (2 each from the high density and walls, ceilings (when it’s low), behind and under furniture/the medium density areas). Poor or worst ventilated houses wall hangings etc. • 936 •
  • 37. ●● For practical purposes, while undertaking mosquito No. of houses positive for Aedes larvae surveillance, one insect collector should spend at least 15 HI = x 100 No. of houses inspected minutes in each of the 4 fixed and each of the 4 random stations. Thus, 2 insect catchers should be deputed; one Container Index (CI) : Percentage of water-holding containers for the 4 random stations and one for the fixed stations (15 positive for Aedes larvae. minutes at each station) on the day surveillance is being conducted in that sector. No. of positive containers CI = x 100●● While using suction tube, keep the end of rubber tubing No. of containers inspected in your mouth and place the opening of the glass tube 1-2 Breteau Index (BI) : Number of positive containers per 100 cm from the resting mosquito. Move the end closer to the houses in a specific location. mosquito by applying gentle suction to draw the mosquito inside the tube, now place your finger over the tube to keep No. of positive containers the mosquito from flying away. BI = x 100 No. of houses inspected●● Do not collect more than five mosquitoes in one tube. After collection, transfer the mosquitoes in transport cages by (An HI >5% &/or a BI >20 for any locality is an indication gentle blowing. that the locality is dengue sensitive and therefore adequate●● Density of mosquitoes is calculated by the following preventive measures should be taken). formula : (ii) Oviposition Traps : “Ovitraps” provide a sensitive and Total No. of mosquitoes collected economical method for detecting the presence of Ae aegypti Density (Per Man Hour) = Man Hour spent in collection and Ae albopictus in situations where Aedes density is low and general larval surveys produce unsatisfactory results If 2 persons have collected 18 mosquitoes and each man (e.g. when the Breteau Index is < 5). The standard ovitrap is has spent 1 hr each (15 minutes per station), the density is a wide-mouthed glass jar of approximately 250 ml which is calculated by the following method : painted black on the outside to attract the Aedes females to 2 Persons X 1 hr= 2 Man Hour oviposit. A piece of hardboard/ wooden paddle or filter paper is Total mosquitoes collected in 2 Man Hour - 18 placed diagonally inside the glass as an oviposition substrate. Mosquitoes collected Per Man Hour (PMH) - 18/2 = 9 In addition, the jar is partially filled with clean water and Density = 9 PMH placed in a shaded and protected place (rain, people/ animal)Total Catch or spray sheet collection : Involves the use of for oviposition.Pyrethrum for collection of mosquitoes resting indoors (Box - (iii) Adult Survey : Human bare-leg catches (landing / biting2). This is a more efficient method of sampling as it can also catches) of Aedes adults (both male & female) or indoor restingcollect those mosquitoes which are hiding under furniture or collections of adults are normally used to assess adult Aedesresting on high ceilings or where the density of mosquitoes populations. The data collected are calculated to reflect theresting is low. number of female Aedes mosquitoes landing/biting on singleOther types of mosquito sampling devices : The other human bait per hour (e.g. number per man hour). The collectorssampling tools are the window traps, magoon traps, direct bait should move from house to house and not collect in one placecollection and light traps. for more than 15 or 20 minutes. In a similar manner, indoorSurveillance of Aedes mosquitoes resting collections can be made and the data expressed as(i) Larval survey : Three indices are commonly used to record numbers collected per man-hour or per house. Adult indicesAe aegypti and Ae albopictus density levels : can also be elicited just like the larval indices i.e. ‘Adult House Index’, ‘Adult Room Index’ and ‘Adult Breteau Index’.House Index (HI) : Percentage of houses or premises positivefor Aedes larvae. Box - 2 : Total Catch or Spray sheet collection ●● Remove all animals, small items of furniture, food items. Close all windows and doors and close / cover all openings with cloth. ●● Spread white cotton bed sheets to cover the entire surface area (no. of sheets will depend on the size of the room). Ensure that sheets have been placed under furniture also. Sheets placed on furniture should not touch the floor as it will prevent the insecticide from reaching underneath. ●● Prepare the Pyrethrum solution from 2% Pyrethrum extract available to a workable strength of 0.2% by mixing 100 ml of Pyrethrum with 900 ml of Kerosene to make a total volume of 1 litre of prepared soln. of 0.2%. ●● Use a hand sprayer (Flit gun) for spraying. After entering the room first close the door of the room and then start spraying in open spaces and holes in the wall and thereafter proceed to apply spray towards the ceiling until the room is filled with fine mist; always taking care to move in a clockwise direction. After spraying, close the door and keep the room closed for at least 10 min. ●● After 10 min, open the door, move gradually from the doorway picking up the mosquitoes by forceps in a container. A torch may be needed for collection of mosquitoes in rooms. • 937 •
  • 38. Mosquito Control The list of anti-larval chemicals along with their dosages is presented in Appendix ‘D’.Anti-adult measures and anti-larval measures are the two mostimportant mosquito control measures. Personal protection Personal Protectionagainst their bites aids these measures in control of disease. Individual personal protection against mosquito bites isMethods related to environmental management by way of achieved by use of mosquito nets, repellents and protectiveminor manipulations or major engineering steps should always clothing. The details are presented in the Chapter on “Principlesbe an important consideration in overall anti-malaria plan. The of Vector Control”.details of these various mosquito control methods have alreadybeen presented in detail in an earlier chapter on principles of Summaryvector control and the readers are suggested to go through the The mosquitoes are rated as the most important vectorsdetails. amongst the blood sucking arthropods. They belong to phylumAnti-adult Measures Arthropoda, class Insecta, order Diptera & family Culicidae. Amongst the mosquito genera, only Anopheles, Culex, Aedes(a) Residual Insecticides : Indoor residual spray is considered and Mansonia are of importance in India. The mosquitoes areto be the most important tool for controlling mosquito borne further classified as Anophelines which comprises only genusdiseases. This is a more practicable and simpler method Anopheles & Culicine comprising three important genera viz.of interruption of transmission of disease. However, there Culex, Aedes & Mansonia.are certain conditions under which the absolute efficacy ofthis procedure may be doubted, for instance, where vector is The length of the mosquito is about 1 cm and the body isexophilic though biting indoors or where the surfaces sprayed divided into head, thorax & abdomen. Head has two compoundare subject to frequent mud plastering or white washing. Even eyes, antennae & mouth parts collectively called proboscis.when local conditions do not appear to be absolutely favourable, Males can be identified by their densely haired antennae whichthe application of residual insecticide gives relative success in look like moustache. Thorax in all the three genera of Culicinesdisease control. DDT, Malathion and the members of synthetic is humped. Mosquito undergoes complete metamorphosispyrethroids like Cyfluthrin, Deltamethrin etc. are the residual through stages of egg larva, pupa & adult. Numbers of eggsinsecticides of choice depending upon the susceptibility of the laid vary between 50 & 150. Larvae pass through 4 instars invectors. The dosages and formulations of common adulticides 5 days and become a pupa. Duration of lifecycle varies betweenused in mosquito control are given in Appendix ‘C’. 7 days to 1 month. Female mosquitoes are blood suckers (anthropophilic - prefer to feed on humans & zoophilic- prefer(b) Space Sprays : Space treatments are usually designed to feed on animals). Mosquitoes as per their biting habits mayto provide rapid knock-down and mortality with little or either be exophagus or endophagus and depending on theirno residual effect. Such treatments must be considered in resting preference may be endophilic or exophilic. Males feedconjunction with other control methods as part of an integrated on plant juices & flower nectar.vector management programme. The details of space sprayingand other adult measures are given in the Chapter on “Principles The genus Anopheles comprises 58 species in India, of which 9of Vector Control”. are vector species with most of them being anthropophilic. Culex adults are dull in colour & have unspotted wings and preferAnti-larval Measures stagnant water. Culex quinquefasciatus is the main vector ofLarval control is the only effective method of radical mosquito bancroftian filariasis in India. Chief species of Aedes in Indiacontrol. In urban areas, this method complements the adult are aegypti, albopictus & vittatus. They are well adapted formosquito control. Anti-larval work is carried out by preventing breeding in small containers of water such as masonary tanks,breeding and destruction of larvae and pupae. For long term earthenware pots, small and large tins, barrel drums, coconutand permanent mosquito control, greater emphasis should be shells, stored or discarded motor car tyres, junk and hardware,placed on the prevention of breeding during non-transmission flower pots, fire buckets, depressions in tree trunks, axils ofseason than on larvicidal measures during breeding season. leaves & tree holes. Aedes mosquitoes are the vectors of urban(a) Vector Engineering : Avoidance of man-made mosquitogenic and rural yellow fever (not found in India), dengue, dengueconditions is of primary importance. The details are presented haemorrhagic fever and chikungunya. Mansonia species layin the Chapter on “Principles of Vector Control”. eggs in cluster anchored to the under surface of the leaves of aquatic plants.(b) Dry Day : Intermittent drying once a week is an effectivemethod of prevention of breeding especially for container Mosquito surveillance is done to elicit information on vectorbreeders like Aedes by observance of a weekly ‘dry day’. All fire density and major characteristics of vectors, to forecast anfighting tanks, ornamental ponds or water storage tanks, fire impending outbreak and to recommend appropriate strategiesbuckets, and all domestic water containers should be emptied, for mosquito control which would prevent outbreak. It is thusscrubbed and allowed to remain dry for a few hours on the important to identify mosquitoes from other such flies; theyweekly ‘dry day’. are identified by the presence of forward projecting mouthparts or proboscis and wing veination (veins 2, 4 and 5 are branched)(c) Larvicidal Measures : Destruction of larvae is achieved by besides other characteristics. If the wings are spotted, it isapplication of larvicidal oils, Organophosphorus insecticides, generally anopheline mosquitoes; whereas, if the legs areuse of IGR’s, biocides and use of larvivorous fish. The details having silvery stripes against dark black legs, it is Aedesare presented in the Chapter on “Principles of Vector Control”. • 938 •
  • 39. and if there are no spots on the wings or stripes on legs, it is 7) Most important vector of Wuchereria bancrofti is _______Culex adult. If larvae have siphon tube at its abdominal end, it 8) Vector species can be distinguished by their thoracicbelongs to Culicine group. Larvae are sampled using standard pattern in _______________larval laddles & larval density is calculated by dividing the total True or falseno. of larvae by the no. of dips. Adult sampling is generally 9) Mosquitoes can be found in altitudes as high as 4000mts.done using aspirators & suction tube. The mosquito density 10) The palpi & proboscis in Culex female are equal.is calculated by Total no. of mosquitoes collected divided by Answers : (1) a; (2) b; (3) b; (4) a; (5) Anopheles culicifacies;the man hours spent in collection. Other methods are spray (6) Siphon tube; (7) Culex quinquefasciatus; (8) Aedes;sheet collection & use of window trap, magoon trap or direct (9) True; (10) False.bait collection. Aedes larval surveys include computing indicesviz. Container, House & Breteau index. The adult sampling Further Suggested Readingprocedures are the landing catch and resting catch, whereas 1. Service Mike. Medical Entomology for students. 3rd ed. Cambridge : Cambridge University Press, 2004.breeding can be detected by oviposition traps. 2. Foster WA, Walker ED. Mosquitoes (Culicidae). In : Medical and Veterinary Entomology, ed. Mullen G, Durden L. Amsterdam : Academic Press, 2002;Study Exercises 203-62.MCQs & Exercises 3. Kettle DS. Medical and Veterinary Entomology. 2nd ed. CAB International, 1995.1) Wings in mosquito are attached to (a) Thorax (b) Abdomen 4. Hati AK. Medical Entomology. Allied Book Agency, Kolkata, 2001. (c) Both (d) None 5. Rozendaal Jan A. Vector control : Methods for use by individuals and2) Branched veins in a mosquito wing are (a) 1,3,6 (b) 2,4,5 communities. Geneva : World Health Organization, 1997. (c) 2,4 (d) 1,6. 6. Nelson MJ. Aedes aegypti : Biology and Ecology. Pan American Health Organisation. Washington, 1986.3) Eggs are laid in rafts in (a) Aedes (b) Culex (c) Anopheles 7. Rao TR. The Anophelines of India. Revised Ed 1983. Malaria Research Centre (d) Mansonia. (Indian Council of Medical Research), Govt of India, Delhi.4) Boat shaped eggs with lateral floats and larva without 8. WHO. Entomological Field techniques for Malaria control. Part 1 : Learners Guide. WHO, Geneva, 1992. siphon tubes are features of (a) Anopheles (b) Aedes 9. WHO. Entomological Field techniques for Malaria control. Part 1 : Tutor’s (c) Culex (d) Mansonia. Guide. WHO, Geneva, 1992.Fill in the Blanks : 10. Das Bina Pani, Rajagopal R, Akiyama J. Pictorial key to the species of Indian Anopheline Mosquitoes. Journal of Pure & Appl Zoology 1990; 2(3) : 131-5) ________________ is the main rural vector of Malaria. 62.6) Respiratory apparatus in larvae of Culicine is __________ Appendix ‘A’ : Mosquito Larval Surveillance Register Anopheles Culex Aedes No. of Sector Larvae/ Larvae/ Date Total Total container No. No. of dip and No. of dip and Type of Remarks larvae & larvae & Positive dips Pupae/ dips Pupae/ container (**) pupae pupae for dip dip breeding (**) Remarks to include details of House index, Container and Breteau index for Aedes if situation warrants. Appendix ‘B’ : Adult Mosquito Surveillance Register Fixed catching Random catching Total Density Sector station station Date Species Per Man No. No. No. Time Time Time No. collected Hour collected collected spent spent spent M F M F M F Total Anopheles Culex Aedes Anopheles Culex Aedes • 939 •
  • 40. Appendix ‘C’: Insecticides Used for Indoor Residual Spray with Dosage and Residual Efficacy Preparation Area to be Residual No. of spray of Dosage sprayed by Insecticide effect in rounds/ Remarks suspension of a.i. 10 lit of weeks annum in water / sq m suspension DDT 50% WP 1 kg/ 10 lit 1g 10 - 12 2 500 sq m In North East only Malathion 25% WP 2 kg/ 10 lit 2g 6-8 3 250 sq m In DDT resistant areas Deltamethrin 2.5% WP 400 g/ 10 lit 20 mg 10 - 12 2 500 sq m In Malathion resistant areas Cyfluthrin 10% WP 125 g/ 10 lit 25 mg 10 - 12 2 500 sq m In Malathion resistant areas Appendix ‘D’ : Insecticides Used for Mosquito Larval Control Area in linear metre to be sprayed by Frequency of Insecticide Dilution rate Dosage /sq m Remarks 10 lit of solution/ application suspension MLO As it is 20 ml 500 Weekly Applied along shore of water body Temephos 2.5 ml in 10 lit for water 20 ml 500 Weekly Applied in all water 50% EC depth up to 50 cm. 5 ml in bodies 10 lit for >50 cm depth Fenthion 5 ml in 10 lit for water depth 20 ml 500 Weekly Not used in potable 82.5% EC up to 50 cm. 25 ml in 10 lit water for >50 cm depth Fenthion 2G - Not used in potable water Bacillus 250 g in 10 lit 20 ml 500 Fortnightly Not used in potable thuringiensis water H -14 (12 AS) Bacillus 500 g in 10 lit 20 ml 500 Once in three Not used in potable sphaericus weeks water and sub-species. Fleas can be classified into two main groups 158 Fleas viz. the combless fleas and the combed fleas, depending on whether they have chitinsed teeth like structure called ‘genal comb’ around the mouth, or not. Rina Tilak The Combless fleas contain the important genus Xenopsylla which has about sixty species and sub-species including theFleas are one of the few important vectors which have been well known vectors of plague viz, X cheopis, X astia and Xhistorically linked with mankind the world over, since time braziliensis. The oriental rat flea (Fig. - 1), X cheopis, is widelyimmemorial. Plague, transmitted by rat flea, was one of the distributed in the tropics and is the principal vector of plaguevector borne diseases which played an important role in in India. X astia is also found in India, Burma, Sri Lanka,redefining geographical boundaries for many centuries. Hongkong and Iran. X braziliensis is found in Africa, especiallyDistribution in Nigeria, Congo, Kenya and in South America but in India itsFleas are distributed all over the world and belong to the order distribution is very restricted. The other important comblessSiphonaptera comprising about twenty five hundred species flea is Pulex irritans (Human flea), which occurs only in the • 940 •
  • 41. hills of the tropical countries of the Eastern Hemisphere. It sucking blood, which forms the only food for both sexes. Thebreeds in and around dwellings and principally attacks man thorax of the flea is compact without any wings. The legs arebesides animals and rats. long and powerful and are adapted for the purpose of hopping and jumping. The abdomen consists of 10 segments, the 9th Fig. - 1 : Adult Rat Flea and 10th being modified for sexual functions. In the female, the abdomen has a rounded terminal outline whereas in the male it has a rather cocked up appearance. The body and the legs are provided with stiff setae, which give the insect a bristly appearance. The tapering pharynx continues into the oesophagus leading into the conical proventriculus. This is an important structure involved in the transmission of bubonic plague. Life History The flea undergoes a complete metamorphosis through the successive stages of egg, larva, pupa and adult (Fig. - 3). When the female is ready to lay eggs, it leaves the body of the vertebrate host and lays eggs in dark place in the hosts nest, debris, accumulation of dust, in cracks or crevices in the floorThe Combed fleas are the cat fleas - Ctenocephalides felis (Fig. of granaries etc. or under carpets in houses. During her lifetime- 2), the dog flea - C canis and the rat fleas of temperate zones, of 6 months or a year, the female lays 300 to 500 eggs in smallNosopsyllus fasciatus. In addition to the genal comb, they also batches of about a dozen at a time. A temperature betweenpossess ‘pronotal comb’ on the thorax (Fig. - 2). These fleas 18°C and 27°C and humidity about 70% favour egg laying.serve as intermediate host of certain veterinary cestodes (dog- However, most fleas complete their life cycle in one to twotapeworm) but are more of a biting nuisance to man. Tunga months. The eggs are just visible to the naked eye and hatch inpenetrans, a sandflea is found in tropical and sub-tropical 2-10 days depending on temperature and humidity. The larvaeregions of North and South Americas, Africa and occasionally are very active, slender, 13 segmented and yellowish whitein Western India. with a number of bristles. They feed on the excreta of rodents and on partially digested blood discharged from the faeces of Fig. - 2 : Adult Cat Flea adult fleas. Larvae complete their development in a week or two and enter quiescent stage, spin cocoons which are whitish, translucent and so loosely spun that the pupae can be seen within them. Hence the pupa closely resembles the adult which usually emerges within a week. It is important to note that presence of ground vibration (caused by movement of hosts i.e. rodents, animals, humans or earthquakes) is essential for the emergence of adult from the pupa. The whole metamorphosis takes two to four weeks, but may need several months under less favourable conditions. Fig. - 3 : Life Cycle of FleaMorphologyAdult fleas are small, bilaterally compressed, highly chitinised,wingless, 6 legged, blood sucking ectoparasites of many warmblooded vertebrates. The size varies from 1.5 to 6 mm in lengthand the colour from light amber to dark brown.They have a compact appearance without a sharp divisionbetween the head, thorax and abdomen. The head is roughlytriangular and bears a pair of three segmented antennae, themouth parts and in certain flea species, a row of powerful teethlike spines collectively known as the ‘genal comb’, arrangedon the lower border of the head, and a set of ‘pronotal combs’on the thorax. However, the rat fleas are devoid of both thesecombs. The mouth parts are adapted for biting, piercing and • 941 •
  • 42. Bionomics for a very short duration. A partially blocked flea is thus moreThe adult fleas are temporarily parasitic on their host while efficient in transmitting plague as compared to a completelytheir immature forms are free living. Both, males and females blocked flea.are haematophagous and frequently leave the host between Endemic typhus is transmitted through the faeces of the ratblood feeds. After the death of the host, its body becomes cold flea which contains the semi digested blood along with theand the flea seeks a new host. Fleas feed frequently and much causative organism R typhi. The flea has a habit of defaecatingmore than their actual requirements, and as a result much of while feeding and hence while scratching the bitten area; thethe ingested blood is passed out in a semi-digested state. Fleas organism finds its way in to the host’s body. The organismare not strictly host specific and may attack unusual hosts can also find an entry into the body through conjunctiva,when hungry or with rise of ambient temperature, when they inhalation and skin abrasions and also by accidental ingestionfeed more frequently. They are very sensitive to light and air of infected flea.currents. They always hide under dark objects and when blown Flea Controlup, they at once get agitated. Adult fleas can survive several Chemical control of fleas is one of the best methods of fleamonths without food. They are able to jump up to 16 cm and control. These are effective against both adult as well ashop 30 cm. larval fleas. The areas or places generally frequented by fleasVector Potential like rodent burrows and rat runs are treated. The insecticidalFlea transmits mainly the zoonoses to man, chiefly from treatment is either done in the form of residual sprays, dustingrodents and also from dogs and cat. The most important or treatment of rodent burrows. Dusting is done by applying amicroorganism that is conveyed to man from rat is Yersinia patch of insecticide dust of about 20-25cm wide and 0.5cm thickpestis causing bubonic plague. The most important vector in all infested areas. For rodent burrows, 30 g of insecticidalspecies is X cheopis, however, X astia and X braziliensis are dust is used.also effective vectors. Rickettsia typhi, causative organism of In plague susceptible areas, treatment is undertaken when fleaendemic (murine) typhus, is also transmitted from its rodent index i.e. X cheopis index exceeds 1 (the other flea indices arereservoir to man by the same rat fleas. Cat and dog tapeworms presented in Box - 1). However, during an outbreak, no rodentuse fleas as their intermediate hosts for the development of control activity is undertaken. In the event of a plague casecysticercoid stages. Cats and dogs become infested by the occurring, immediate treatment of the patients dwelling and ofingestion of infested fleas. Children also get infected similarly other dwellings within 200 m is undertaken.due to accidental ingestion of the infected fleas. The South (a) Vector Control : DDT has become non-effective againstAmerican and African flea Tunga penetrans burrows under the fleas in many parts of the world. Malathion resistance has alsosoft skin in between toes and under the nail bed and causes a appeared in certain parts of India. Prior susceptibility testsdisease called chigger, jigger or chigoe in endemic areas. should be carried out to find out the most effective insecticide.Modes of Transmission of Diseases Indoor residual spraying at the lower one metre of the wallBubonic plague is transmitted by infected fleas called ‘Blocked surface and adjacent floor area is effective. Patch dusting alsoflea’. When a flea (Xenopsylla species) feeds on a host suffering brings about marked reduction in flea density. For this, dusts offrom plague, it ingests plague bacilli (Y pestis) along with the Propoxur (1%), Malathion (5%) or Carbaryl (5%) may be appliedblood meal. The blood is digested in the stomach, however, the at a dosage of 2 to 3 g per m2 of surface area under grain bins,bacilli rapidly multiply and block the proventriculus thereby on rat runs, furniture, upholstery, rugs and bedding. The dustrendering the proventriculus partially blocked and incapable of Deltamethrin (0.05%) may also be used for dusting in rodentof preventing regurgitation of stomach contents (the normal infested area.role or functioning of the proventriculus) while feeding. Since (b) Disinfestation : Disinfestations of pet animals like dogsthe stomach is filled with plague bacilli, the amount of blood and cats along with good environmental sanitation of thedigested is minimal and hence this flea feels hungrier and bites household and public places (by keeping houses well sweptrepeatedly and in the process, regurgitates plague bacilli in the and floors washed) help in flea control. Pet animals may bewound thus causing plague in the host. After a few days, the treated with dusts, sprays or dips of Malathion, Propoxur,multiplying plague bacilli completely block the proventriculus Permethrin or Pyriproxyfen. Animal premises may be sprayedthus rendering it totally ineffective in preventing regurgitation. with insecticides (Malathion, Deltamethrin, Pyrethrum etc.)Since no amount of blood gets digested, this flea though bites @ 4 - 8 l/100 m2. Insecticidal treatment of animals and theirrepeatedly and inoculates the bite wound with bacilli, lives premises should be carried out simultaneously. Lufenuron Box - 1 : Flea Indices ●● General flea index - Average number of fleas (all species included) per rodent. e.g. if, in all, 20 fleas were recovered from a total of 4 rodents examined, the index would be 20/4 = 5. ●● Specific flea index - (important is X cheopis index). This is same as general flea index but calculated exclusively for X cheopis. e.g. in above example, if a total of 2 of the 20 fleas were X cheopis, this index would be 2 / 4 = 0.5 ●● Percentage incidence of flea species - This is the percentage of each species of fleas, out of the total fleas sampled per rodent. ●● Rodent infestation rate - If 10 rodents were caught and 6 were infested with fleas, this index would be 6/10=60% • 942 •
  • 43. tablets are recent introduction in the armoury of flea control known vectors of plague viz, X cheopis (Rat flea), X astia and Xmeasures against cats and dogs; it is taken up by the female braziliensis. The combed fleas are the cat fleas - Ctenocephalidesflea during feeding and acts by inhibiting egg development. felis, the dog flea, C canis and the rat fleas of temperateA dose of 30 mg Lufenuron per Kg of body weight for cats zones, Nosopsyllus fasciatus. Adult fleas are small, bilaterally& 10 mg/Kg of body weight for dogs is ideal for flea control. compressed, highly chitinised, wingless, 6 legged, bloodDetails of insecticides used in flea control are shown in sucking ectoparasites of many warm blooded vertebrates. TheTable - 1. mouth parts are adapted for biting, piercing and sucking blood, which forms the only food for both sexes. The flea undergoes a Table - 1 : Flea control measures complete metamorphosis through the successive stages of egg, Concen- larva, pupa and adult. Eggs are laid in dark place in the hosts Insecticide Dilution nest, debris, accumulation of dust, in cracks or crevices in the tration floor of granaries etc. or under carpets in dwelling houses. A a) For Fleas : temperature of 18° and 27°C and humidity about 70% favour Propoxur 20% 1% Mix 50 ml + 950 ml water egg laying. The adult fleas are temporarily parasitic on their Malathion 50% 5% Mix 100 ml + 900 ml water host while their immature forms are free living. Both males and females are haematophagous. Deltamethrin 2.5% 0.05% Mix 20 ml + 980 ml water Flea transmits mainly the zoonoses to man, chiefly from b) For Animal treatment: rodents and also from dogs and cat. The most important Propoxur 1% 1% spray/ As it is microorganism that is conveyed to man from rat is Yersinia dust pestis causing bubonic plague. Rickettsia typhi, causative organism of endemic typhus, is also transmitted from its Malathion 50% 0.25% Dip Mix 5ml in 1 l of water rodent reservoir to man by the same rat fleas. Bubonic plague Deltamethrin 0.0025% As it is is transmitted by infected fleas called ‘Blocked flea’; Endemic 0.0025% shampoo typhus is transmitted through the faeces of the rat flea. Permethrin 1% 1% As it is Chemical control of fleas is one of the best methods of flea shampoo control effective against both adults & larvae. The insecticidal c) For Premises : treatment is either done in the form of residual sprays, dusting or treatment of rodent burrows. In Plague susceptible areas, Pyrethrum 0.2% Mix 100 ml + 900 ml water control is undertaken when flea index i.e. X cheopis index 2% Extract (the average number of fleas per rodent) exceeds 1. However, Malathion 50% 2% Mix 40 ml + 960 ml water during an outbreak, no rodent control activity is undertaken. Chlorpyrifos 20% 0.5% Mix 25 ml + 975 ml water Flea control can be achieved by Indoor Residual Spraying using Propoxur (1%), Malathion (5%) or Carbaryl (5%). Disinfestation(c) Rodent Control : It is an indirect method of flea control. of pet animals like dogs and cats and use of flea collar, alongThough a radically effective method during non-epidemic with good environmental sanitation of the household andperiod, it is dangerous during epidemics, because the fleas leave public places helps in flea control. Use of a high charpoy,dead rats quickly and starts attacking human beings. However, insecticide treated nets and application of repellents viz. DEETa constantly sustained campaign keeps the rodent population are necessary precautions while in endemic or epidemic areasdown and aids significantly in keeping the flea index constantly of flea borne disease.low. In general, during control of urban plague, insecticides to Study Exerciseskill rat fleas should be applied a few days earlier or at leastat same time (and not after) when rat poison baits are being Short Notes : (1) Blocked Flea (2) Flea Index.applied. The detail on rat poisons is presented in the chapter MCQson rodents. 1) Combed flea is (a) Xenopsylla cheopis (b) Xenopsylla astia(d) Personal Protection : This is achieved by the use of (c) Pulex irritans (d) Ctenocephalides felis.protective clothing such as wearing long trousers, socks and 2) Flea transmits all except (a) Bubonic Plague (b) Endemicshoes. Use of a high charpoy with the net, and application of typhus (c) Epidemic typhus (d) Chiggerosis.repellents viz. DEET are necessary precautions while in endemic 3) The insecticides that can be used for flea control areor epidemic areas of flea borne disease. Using flea collars for (a) Propoxur (b) Malathion (c) Deltamethrin (d) All.pets are effective means of keeping them free from infestation Fill in the Blanks(for 3-4 months). 4) The Rat flea lives for a duration of ______________ 5) Average no. of fleas per rodent gives the ______________Summary True or falseFleas are important vectors, linked with mankind since long. 6) Presence of ground vibration (caused by movement of hostsFleas can be classified into two main groups, combless fleas i.e. rodents, animals, humans or earthquakes) is essentialand the combed fleas. The combs can be genal comb arranged for the emergence of adult from the pupa.on the lower border of the head or pronotal combs on the thoax. 7) A partially blocked flea is more efficient in transmittingXenopsylla species are combless fleas and include the well plague as compared to a completely blocked flea. • 943 •
  • 44. Answers : (1) d; (2) c; (3) d (4) 06 months to 01 year; (5) Flea 2. Rothschild M. Recent advances in our knowledge of the order Siphonaptera. Annual review of Entomology 1975; 20 : 241-59.Index; (6) True; (7) True. 3. WHO. Fleas Training and Information guide. WHO, Geneva, 1985. WHO/VBC/ TS/85.1.Further Suggested Reading 4. Hinkle NC, Rust MK, Reierson DA. Biorational approaches to flea1. Gratz NG, Brown AWA. Fleas biology and control. Geneva : World Health (Siphonaptera : Pulicidae) suppression : present and future. Journal of Organisation, 1983. WHO/VBC/83.874. Agricultural Entomology 1997; 14: 309-21. is bilobed while in the male, it is pointed from which the 159 Human Lice aedeagus (penis) projects. Phthirus resembles Pediculus in its general morphology, but its body is almost circular, all the three pairs of legs of Pediculus are equal whereas in Phthirus, the Rina Tilak first pair is less developed. P capitis has a smaller and deeply pigmented body, while that of P humanus is larger and non-Human lice are true ecto-parasites of man. There are three pigmented. Abdominal segments of P humanus are roundedspecies of human lice viz. Pediculus capitis (head louse), with shallower inter segmental indentations while those ofPediculus humanus (body louse) and Phthirus pubis (crab or P capitis are clearly marked and deeper. Antennae and legspubic louse). Adults (both female & male) as well as nymphs of P humanus are longer and thinner than those of P capitisare haematophagous, however, only body louse has been (Fig. - 1 & 2).incriminated as vector. Life HistoryThe head louse infests the hair on the head and may be foundin the neck region and behind the ears. The body louse infests The life histories of all the three varieties are similarthe hairs of chest and axilla, seams of clothing in contact with (Fig. - 3). After fertilization, the female lays eggs either on thethe body and sometimes linen. The crab louse infests the hair hairs or under clothing chiefly along the seams of the vests, pantsof the pubic region and occasionally invades eyelashes and and shirts etc. Freshly laid eggs are white and proportionallyeyebrows. large for the size of the insect. They are firmly cemented to the hair or seams of the clothing, singly or in groups. As theMorphology embryos develop they become yellowish. The number of eggsLice are small (4.5mm), dorso-ventrally flattened, wingless laid depends upon the food supply and the temperature. Underinsects with simple metamorphosis. They are permanent optimum favourable conditions, the louse lays 4 to 9 eggs inobligatory ecto-parasites living entirely on mammals. The each batch. Total number of eggs laid during the life span ofmouthparts are of a sucking and piercing type. They have 4 to 5 weeks may be 300 in a body louse, 150 in a head louseno eyes. The legs are short, stout, and thick with claws for and 50 in a crab louse. Within a weeks time, the immaturegrasping hairs and fibres. The abdomen is oval or somewhat stages called nymph emerge and begin sucking blood at oncecircular in shape. In the females, the last abdominal segment and throughout their development feed frequently during the Fig. - 1 : Head Louse Fig. - 2 : Body Louse • 944 •
  • 45. day and night, mostly when the host is quiet. There are three Vector Potentialnymphal stages and the young ones resemble the adults except Body lice are responsible for the transmission of Rickettsiain size. It takes about 21 days between hatching of the eggs prowazeki, causing Epidemic typhus, Bartonella quintanaand appearance of the adults. causing Trench fever, and Borrelia recurrentis causing Relapsing fever. The presence of lice on any part of the body Fig. - 3 : Life history of Lice is termed ‘pediculosis’ which causes irritation with loss of sleep and scratching which may lead to secondary infections. Toxic reactions to the saliva injected into the skin may lead to weariness and a general feeling of illness. The skin of a heavily louse infested person becomes hardened and deeply pigmented and results in a condition known as ‘Vagabonds’ disease or melanoderma. Prevention and Control Regular washing of hair with soap and warm water and combing with lice comb may prevent/reduce head lice infestation. Similarly, regular washing of clothes with hot water (more than 60°C) and ironing and changing of clothes prevents body louse infestations. In the past, use of anti louse powder (10% DDT) was used for reduction of infestation in a controlled community by dusting the lousy individuals and garments. Currently, the insecticides of choice are Permethrin dust (0.5%), Propoxur dust (1.0%); for mass treatments against body louse, dusts should be applied through neck openings, up sleeves and from all sides of the loosened waist of trousers. Socks, head coverings, the inner surfaces of extra garments and bedding should also be treated. Treatment of clothing with synthetic pyrethroid or use of pretreated uniforms may prove an effective means of prevention of body lice infestation amongst Armed Forces personnel during war.Bionomics Shampoo formulations like Phenothrin (0.2-0.4%), PermethrinLice prefer warm and moist environments; 38°C is the optimum (1%) and Malathion (5%) lotion are ideally used for head licetemperature. Higher temperature and death of the host are infestation. For application on hair, the hair of the infesteddetrimental and make lice leave the body of the host. The persons should be wetted thoroughly before application. Theaverage life of a louse is 30 to 50 days. Females live longer insecticidal shampoo is thoroughly massaged on the head andthan the males. left for minimum 10 min. Thereafter, the shampoo is rinsed offOnce lice are acquired by a human host, their multiplication from the hair, hair is towel dried and combed with lice comb todepends on the neglect of personal hygiene. Following factors remove dead/ stunned lice.are responsible for the dissemination of lice.(a) Close contact with lousy persons; sharing the same bed Summary and clothing etc. In fact any prolonged crowding of human Human lice are true ecto-parasites of man. There are three beings in unsanitary surroundings will spread lousiness. species of human lice viz. Pediculus capitis (head lice), Hence lice and louse borne diseases are closely associated Pediculus humanus (body louse) and Phthirus pubis (crab or with wars and disasters among prisoners and refugees. pubic). They are obligatory ecto-parasites living entirely on(b) Indirect contact - for example exchange of beddings, mammals. After fertilization, the female lays eggs either on clothing, blankets, towels, hats, combs and brushes. the hairs or under clothing chiefly along the seams of the vests,(c) Hair bearing eggs from lousy persons scattered in public pants and shirts etc. The number of eggs laid depends upon the conveyance are picked up from the seats and cushions of food supply and the temperature (38°C). It takes about 18 days railway carriages and buses etc. between hatching of the eggs and appearance of the adults.(d) Head lice easily pass from one child to another in school by Dissemination of lice occurs with close contact, in unsanitary close contact while playing and also by sharing of combs. surroundings, exchange of beddings, hats, comb & brushes.(e) The pubic or crab lice spread through sexual contact and Transmission occurs through public conveyance, in school & sometimes from toilet seats, beds and by close personal through sexual contact. contact. Small children may become infested with crab lice Body lice are responsible for the transmission of Rickettsia on their eyebrows and eyelashes from their mothers or prowazeki, causing Epidemic typhus, Bartonella quintana other close contact. causing Trench fever, and Borrelia recurrentis causing Relapsing fever. Insecticides of choice are Permethrin dust (0.5%), Propoxur • 945 •
  • 46. dust (1.0%) and insecticide treated uniforms for body louse and Answers : (1) d; (2) d; (3) Pediculosis; (4) Mass treatment,shampoo formulations like Phenothrin (0.2-0.4%), Permethrin body.(1%) and Malathion (5%) for head lice infestation. Further Suggested ReadingStudy Exercises 1. Vector control : Methods for use by individuals and communities, Jan A.Rozendaal World Health Organization Geneva 1997.MCQs & Exercises 2. Birendra Nath Ghosh; A treatise on hygiene and public health, 14th edition,1) Lice cause all of the following except (a) Epidemic Typhus 1965, Calcutta scientific publishing co. (b) Trench fever (c) Relapsing fever (d) Endemic Typhus 3. Gratz, N. Human lice, their prevalence and resistance to insecticides. 1998. Geneva : WHO.2) Body louse infests (a) Hair on chest & axilla (b) Seams of 4. Chunge RN, Scott FE, Underwood JE, et al. A review of the epidemiology, clothing (c) Linen (d) All public health importance, treatment and control of head lice. Can J Public Health 1991; 82 : 196-200.Fill in the Blanks : 5. Reeves JR. Head lice and scabies in children. Pediatr Infect Dis J 1987; 6 :3) Presence of lice on any part of the body is called as _____ 598-602.4) Dust application through neck openings, up sleeves & 6. Bachok N, Nordin RB, Awang CW, Ibrahim NA, Naing L Prevalence and trousers is used for _________ against __________ louse. associated factors of head lice infestation among primary schoolchildren in Kelantan, Malaysia. Southeast Asian J Trop Med Public Health. 2006; 37(3):536-43. Life History 160 Sand Flies Fig. - 1 : Sand Fly - Morphology and Life Cycle Rina Tilak Egg Larva PupaSand-flies bite humans and transmit diseases to them. Thereare about 700 species of sand-flies of which only 70 specieshave been incriminated as vectors so far. The sand-flies belongto the subfamily Phlebotominae of the family Psychodidae.The haematophagous species belong to the three genera of WingPhlebotomus, Lutzomyia and Sergentomyiay, the former two Venationbeing more important as vectors of diseases. The medicallyimportant Phlebotomus vector species in India includeP argentipes, P papatasii, P sergenti and P braziliensis.MorphologyThe adult sand-fly is a small, greyish yellow to brown insect Femaleand about 1.5 to 4.0 mm in size. The insect is typicallycharacterized by large conspicuous eyes and stilt like legs. Theentire body is densely covered with hair. The antennae are long Malefilamentous and give a beaded appearance. The mouth partsare very short and are adapted for biting and piercing in thefemales. The thorax is markedly humped and bears a pair oflanceolate wings which are held erect over the body when thefly is at rest. The wings are densely hairy and the second veinbranches twice, the first branching in the centre of the wingand second at the margin. Legs are long, slender and used forhopping as sand-flies are poor fliers. The abdomen consists of10 segments; the last two are modified for sexual functions. The sand-flies prefer to breed in dark places rich in organicThe abdomen of a female is rounded posteriorly; in the males, matter and moisture. Sand-flies lay torpedo shaped eggs in smallit is modified and bears claspers (Fig. - 1). batches which hatch out in one or two weeks under optimum • 946 •
  • 47. favourable conditions. The larvae are legless and whitish with it difficult for the larvae to burrow. Empty buildings should bea dark head capsule and pass through four instars. The larvae kept in good repairs; soak pits and grease traps should be wellfeed on organic excrement of lizards and mammals and other maintained.decaying material. Its life span is from 2 to 6 weeks, depending (b) Anti-larval Measures : Anti larval measures are generallyon the temperature and humidity. The larva bears two anal difficult to undertake as identification of larval breeding sitesspines. The pupa is golden brown in colour and naked and is difficult. Even if insecticidal control is planned, it has beenrequires about 10 days for development after which the adult found to be of little importance in the control of sand-flies.emerges. Male sand flies emerge about 24 h before females, (c) Anti-adult Measures : Anti adult measures are based on thefor their external genitalia to rotate 180° for achieving the principle that sand-flies make short flights with relatively longcorrect position for mating before the females have emerged. pauses on entering or leaving any place or shelter. Therefore,The total period required from egg to the adult stage is about 4 any surface treated with residual insecticide on which the fliesweeks under favourable conditions. In the tropics, the breeding rest will have a lethal impact. The anti adult measures are thegoes on throughout the year. In north India, they appear about same as followed under the National Programme for Indoorthe middle of March and persist until November, with their residual spraying against mosquitoes; this strategy has provedmaximum density in March and April. to have a dramatic impact on the density of sand-flies in theBionomics area. If outdoor resting sites have been identified, they can alsoThe sandflies live entirely on plant juices or similar fluids from be sprayed with residual insecticides. Outdoor fogging mayother available sources but the females need a blood meal provide additional benefit in reduction of Sand-fly density.in order to develop eggs. Phlebotomines are crepuscular or (d) Personal Protection : Use of repellents viz. DEET is one ofnocturnal biters and most of the biting occurs outdoors with the most efficient methods of preventing bites from sand-flies;only a few species feeding indoors. The adults are weak fliers the repellents may be applied topically or sprayed on clothes.and generally confine themselves up to 50 yd from their breeding A sand-fly net is useful, but it reduces air movements andplace and are not found resting beyond 3 ft on the wall. After causes great discomfort. Use of insecticide treated mosquitofertilization and a blood meal, the female lays eggs in shady, nets has been found very effective in protecting against bites ofdamp and warm places with sufficient supply of organic matter sand-flies. Personal protection may also be achieved by barriersuch as insect remnants and faeces and excrements of tiny clothing.animals which form the future larval food. Such conditions (e) Other Measures: These include encouragement of gardeningare found under stones, in stables and poultry houses, around (cultivation of ground) and planning of embankments withsoakage pits, grease traps and water sinks, in hollowed trees native aromatic plants. Free cross ventilation and ingress ofand rodent burrows, bases of walls and embankments. Large sunlight keeps the sand-fly out of habitations or animal sheds.population of sandflies can build up in dwellings where cattle Electric fans are useful as the air current drives them away.are kept at night; the cattle provide an abundant source of Electric light shades smeared with Vaseline, traps a largeblood, while the stables and houses provide suitable resting number of sand-flies. Siting of human habitation beyond 50place. yards of the breeding place is an effective method of preventingVector Potential transmission of sand-fly borne diseases as also sleeping onSand-flies are responsible for the transmission of various cots.species of Leishmania causing Kala-azar or Visceral (f) Treatment of Animals: Earlier practice of culling of dogsleishmaniasis, Oriental sore or Cutaneous leishmaniasis, or killing of rodents is no more undertaken. Dogs are treatedand Espundia or Mucocutaneous leishmniasis (naso-oral). by dipping in insecticide solution (Deltamethrin 50 ppm) orSand-flies also transmit the virus of sand-fly fever, also applying insecticide solution (1-2 ml of 65% Permethrin orknown as papatasi or Phlebotomus fever or 3 day fever and Imidacloprid 10%). Even insecticide treated dog collars andthe re-emerging viral disease - Chandipura disease. It also treatment of non-reservoir animals reduces transmission oftransmits Bartonella bacilliformis or Oraya fever also known Leishmaniasis.as Bartonellosis or Carrion’s disease. In addition, the sand-flies have biting nuisance causing skin reactions (Herara) insensitized persons. SummaryPhlebotomus Control Sand-flies belong to the subfamily Phlebotominae, bite humans(a) Prevention of Breeding : This is primarily achieved by and transmit diseases to them. The medically important vectorgood environmental tidiness. Places providing humidity, species in India include P argentipes, P papatasii, P sergentidarkness and organic matter should be dealt with by removing and P braziliensis. The adult sand-fly is a small, greyish yellowall collections of rubble and heaps of rubbish; obliterating all to brown insect about 1.5 to 4.0 mm in size; body is denselycracks and fissures in the floors of the buildings and indoor covered with hair. Sandflies possess a pair of lanceolate wings.constructions, sides of culverts, gutters, nullahs, cattle sheds The wings are densely hairy and the second vein branchesand poultry houses which are common breeding places for twice. Sand-flies prefer to breed in dark places rich in organicsand-flies. Cracks and holes in the walls up to a metre from the matter and moisture. Females have piercing mouth parts andground should be sealed by plastering and the earthen floor of are blood suckers. The males live entirely on plant juices orcattle sheds should be rammed down and made hard to make similar fluids from other available sources. After fertilization • 947 •
  • 48. and a blood meal, the female lays eggs in shady, damp and Study Exerciseswarm places with sufficient supply of organic matter such as MCQs & Exercisesinsect remnants and faeces. 1) The vein which branches twice in a sandfly wing is (a) 4 (b)Prevention of breeding is achieved by good environmental 5 (c) 6 (d) 2tidiness. All collections of rubbish should be removed from 2) Sandfly eggs can be laid in (a) Stables (b) Hollow treesplaces providing humidity, darkness and organic matter. (c) Rodent burrows (d) All of theseCracks and holes should be sealed. Earthen floor of cattle sheds 3) Sandfly does not transmit (a) Kala-azar (b) Oriental soreshould be rammed down and made hard to make it difficult (c) Chikungunya (d) Sandfly feverfor the larvae to burrow. The anti adult measures are the same 4) Which of these preventive measures is difficult to undertakeas followed under the National Programme for Indoor residual (a) Prevention of breeding (b) Antilarval measures (c) Antispraying against mosquitoes. Use of repellents like DEET is one adult measures (d) Personal protectionof the most efficient methods of preventing bites from sand- Fill in the Blanksflies. Other methods like treated nets or barrier clothing may beused. Free cross ventilation and ingress of sunlight keeps the 5) The sand-flies belong to the subfamily ______________sandflies out of habitations or animal sheds. 6) The males of sandfly live entirely on _______________ Answers : (1) d; (2) d; (3) c; (4) b; (5) Phlebotominae (6) Plant juices. The silken pupa is also firmly anchored to the substratum. 161 Some Annoying Pests The pupal stage may extend from 4 to 5 days to 2 to 3 weeks. The imago emerges from the submerged pupal case and comes on to the water surface where it rests for a while and after Rina Tilak sometime starts flying. In the tropics and subtropics breeding is continuous throughout the year. The life span of the adult isSimulium Flies about three months.Simulium flies are commonly known as Black flies. They havea world wide distribution. They belong to the family Simulidae, Fig. - 1 : Black Flywhich contains over 1800 species; however, the importantgenera are only four which bite humans and out of these fourgenera, Simulium is the most important. The members ofthis family are found from sea level to a height of 2000 m. InIndia, these have been reported from Kumaon Hills, HimachalPradesh, Kashmir, Assam, Arunachal Pradesh, Manipur,Nagaland, Bengal, Bihar, Maharashtra, Tamil Nadu and NilgiriHills. In Arunachal Pradesh, they are known as Dimdam flies.Life HistoryThe adults are small; stout bodied with a humped thorax andblood sucking flies varying in length from 1 to 5 mm. Thecolour varies from dark amber to bright yellow to orange. Thename “black fly” is therefore, a misnomer.Simulium flies breed in fast flowing turbulent mountainstreams and torrents because they require well aerated water.A female lives for 2 to 3 months and lays several batches ofeggs under the rocks, stones, vegetation or debris submergedjust below the water surface (Fig. - 1). Eggs hatch in one to two Bionomicsdays; in temperate zones the hatching period may be one week.The larvae are attached to submerged objects with their heads Simulids are strong fliers. Their normal flight range is aboutdownstream. They feed on microscopic animals and plants and 4 to 5 km. Flights up to 20 to 40 km with favourable winddo not swim. The larva undergoes six moults in about 10 to are not unusual. Both male and female Simulids feed on plant14 days in the tropics and 3 to 4 weeks in temperate regions. juices, nectar and pollens of flowers; the females however, • 948 •
  • 49. require blood meal for development of eggs and are voracious Fig. - 2 : Bed Bug - Adultand persistent biters. They may enter through any opening inthe clothing such as sleeves or through the lower opening oftrousers for biting. They bite only by day in the open and areespecially active on bright sunny days and retire at night to theneighbouring vegetation where the females mature their eggs.Vector PotentialSeveral species of simulids are known vectors of Onchocerciasis,a filarial disease due to Onchocerca volvulus occurring in tropicalAfrica, Central America and Venezuela, where S damnosum,S mettallicum and S neavei are the vectors. In India, Simulidshowever, are not vectors of any known human disease. But thevery annoying and persistent attacks in large numbers makeworking in the open virtually impossible. The immediate traumacaused by its bite produces a red haemorrhagic spot leading topapule formation. In certain cases, it may lead to secondaryinfections and ulcers like ‘ulcus tropicum.’ In sensitizedpersons, allergic reactions like lymphangitis, lymphadenitis,rhinitis and fever may occur. Their bites are responsible for lossof livestock.Control MeasuresControl of the biting flies has been achieved by use oflarvicides and aerosol treatment. In the Onchocerciasis controlprogramme in Africa, Temephos 200 g/l emulsion has beenused as a larvicide with good results. BTI has also been used Life History@ 0.54 - 0.72 l/m2 with great success. Aerosols and fogs A bed bug passes through egg stage and 4 nymphal stages.produced by fogging machines are useful in killing adult The fertilized females lay flask shaped, operculated eggs singlyflies. Clearing of vegetation around the perimeter also reduces in hidden sites, such as cracks and crevices in the walls andDimdam fly nuisance. Other compounds like Permethrin and floorings, spaces in the wood work of furniture, behind pictures,Etofenprox have also been evaluated and found effective. Use mattresses, pillows etc. A female lays 2 to 10 eggs a day withof protective clothing will prevent the flies from ascending a total up to 200 to 300 in her life time of 6 to 8 months.up the sleeves and trousers or entering into the shirt front. The eggs usually take 5 to 10 days to hatch. The nymph startsSocks should be pulled over the bottom of trousers. Additional feeding within an hour or two after emergence and continuesprotection may be obtained by treating the clothing and the to feed intermittently in all the further stages of development.exposed parts of the body with any of the repellents such as There are four nymphal stages, each lasting 6 to 7 days; atDibutyl phthalate (DBP), Diethyl toluamide (DEET) or Diethyl the end of each, a skin is cast off. It takes 4 to 6 weeks for thephenyl acetamide (DEPA). development from egg stage to adult.Bugs BionomicsBugs (Order Hemiptera) have been associated with man since Adults can subsist without food for months under favourableantiquity. They have a world wide distribution and consist conditions. Bugs are disseminated through travelling bags,of two important families’ viz. Cimicidae and Reduviidae. laundry, furniture, bedding, old charpoys, soiled clothing,Family Cimicidae includes the ‘bed bugs’, Cimex lectularius infested household goods, public conveyance and public places.of temperate regions and C rotundatus or C hemipterus of the Bed bugs like lice have been companions of man for centuries.tropics. Family Reduviidae includes the cone nose Triatomine Hiding in cracks and crevices during the day, they becomebugs, also known as ‘kissing’ or Assasin bugs. In India, bedbugs active during the night and come out of their hiding places tohave a great nuisance value. feed on hosts and engorge completely in 3-6 min. They mayMorphology travel long distances for sucking blood. They are gregarious,Bed bugs are small, 5 to 6 mm long, dorso-ventrally flattened, occurring in great assemblages. All stages are parasitic andwingless, dark brown insects with a mahogany tint (Fig. - 2). thrive on human blood.They have a very short and broad head attached to the thorax. Medical ImportanceThe head bears antennae and a pair of well developed eyes. On Bedbugs have all along been suspected for the transmission ofeither side of the thorax, the stink-glands are situated which various diseases but so far have not been incriminated for anygive off the nasty, pungent or offensive odour associated with human disease. They are of public health importance primarilythis group. for their biting nuisance and demoralizing effect as their infestation may cause insomnia and pruritis / dermatitis. • 949 •
  • 50. Prevention and Control hatch out in 2-6 months in most of the species, depending onThe first and foremost principle for the prevention of bedbug temperature and humidity. The young ones are almost whiteinfestation is to maintain a very high standard of hygiene. and wingless. They moult a number of times and the totalAll furnitures and belongings of new occupants should be developmental period may be 6 months to 1 year. They maythoroughly checked for the presence of bed bugs and immediate produce three generations in a year and usually have a longmeasures taken to prevent their multiplication by one of the life span.appropriate insecticides. Residual insecticides applied directlyinto the hiding places control the bedbugs. Solution of Malathion Fig. - 3 : Cockroaches - Common Domestic Species@2% or Chlorpyrifos @0.5% may be used. Disinfestations Periplanata Blatella Blattaof blankets, beddings, mattresses and mosquito nets may americana germanica orientalisbe carried out by subjecting them to heat at or above 70°C. (American (German (OrientalSynthetic pyrethroids like Bifenthrin (0.096%), Permethrin Cockroach) Cockroach) Cockroach)(0.125%), Cyfluthrin (0.04%) and Deltamethrin (0.03%) canalso be used to achieve optimum results. Residual insecticidalspraying for malaria control undertaken systematically andmethodically will also help in reducing the density of bed bugsas a collateral benefit. Insecticide treated bed-nets will alsohelp in reducing the menace of bed bugs.Debugging : The bed (Bed stand) need not be inclined againstthe wall nor the coir netting loosened. The cots should bethoroughly treated on all sides with insecticidal spray. Allcracks and crevices should be fully flooded. The chairs, tablesand other items of furniture may be similarly treated. Theinsecticide formulation may also be directly applied to thehiding places such as joints, cracks and crevices in the cots/chairs/tables and folds or creases in the mattresses and otheritems of beddings. Fig. - 4 : Egg cases of the domestic cockroachesSlow drip technique involving the use of the common twoinches thick paint brush for treatment of the infested cots andother items of furniture is reportedly superior as compared tothe routine method of spraying with compression sprayer. Inthis technique, the ready to use solution of insecticide in wateris taken in a plastic mug of one litre capacity, a paint brushis dipped in the solution, and the solution so lifted is slowlydrained into the cracks and crevices as well as the joint spaces Bionomicsfrom different directions. The process is repeated by turning the They breed in warm moist places in the humid microclimatecot upside down so that all such hiding places are thoroughly of the kitchen and pantry, laying eggs in cracks, crevices andflooded with insecticide. sinks. They can run swiftly by means of long well developed legs. They are highly gregarious and primarily nocturnal inCockroaches habit, but may be seen during the day as well. The mouth partsOne of the most annoying pests encountered in an urban are adapted for biting and chewing and they are omnivorous,area are the Cockroaches. The common domestic species feeding on any material meant for human consumption likewhich infest buildings are Blatella germanica, the German meat, milk, grains and sugar.roach; Periplaneta americana, the American roach and Blattaorientalis, the Oriental roach (Fig. - 3). The German cockroach, Disease Potentialalthough a native of Europe, is the most widely distributed They are filthy, annoying pests imparting a nauseatingspecies. ‘cockroach’ odour to the food articles and utensils they come in contact with and the places they infest. They destroy food,Morphology damage fabrics, books and other household articles. TheyCockroaches are dorso-ventrally flattened creatures with colour may enter houses and other buildings from outdoors throughvarying from dark brown to black. The head is flexed backward infested containers or from adjoining rooms and apartmentsand the antennae are filiform. Most of the species have two or through drains. On account of their indiscriminate roamingpairs of wings. In some of them the wings are vestigial. In the and feeding habits, they mechanically spread diseases likeoriental cockroach, the wings are short in the females but much cholera, typhoid, dysentery, protozoal cysts, intestinal wormsdeveloped in the males which possess the power of flight. etc. by polluting food with infective material carried on theirLife History legs and bodies.They have simple metamorphosis and lay 16 to 48 capsulatedeggs depending on the cockroach species (Fig. - 4). The eggs • 950 •
  • 51. Control Measures Summary(a) Prevention : This includes : Simulium flies have worldwide distribution & are commonly(i) Good house-keeping is the key to cockroach control, known as Blackflies; in Arunachal Pradesh, they are known as whether in the home, restaurant, hotel or grocery stores. Dimdam flies. As they require well aerated water, they breed(ii) All cracks and crevices should be properly filled up. in fast flowing turbulent mountain streams. The life span of(iii) All areas should be kept thoroughly clean so that no food the adult is about three months. The colour varies from dark particles, debris, dust and rubbish remain to support and amber to bright yellow to orange. Male and female Simulids nourish cockroaches. feed on plant juices; the females require blood meal for(iv) Keeping surveillance on the occurrence or increase in the development of eggs. They can enter through any opening in density of cockroaches in a house by use of sticky traps or the clothing and bite during the day. Simulids are vectors for else by use of visual assessment method, whereby light is Onchocerciasis in some parts of the world; however, they do switched on late in night and the cockroaches counted for a not cause any disease in India. Control can be achieved by the stipulated time period, say five minutes. This method also use of larvicides like temephos & BTI. Use of aerosols & fog indicates the hiding places in a room of the cockroaches with clearing of vegetation is other means of achieving control, besides indicating the level of infestation. besides protective clothing & use of repellants.(b) Control : Cockroach infestation can be controlled with Bugs have a world wide distribution and consist of twoinsecticidal sprays, dusts or baits. The insecticide should be important families’ viz. Cimicidae (bed bugs) and Reduviidaeapplied thoroughly to runways, cracks, crevices, undersides of (kissing bugs). Bed bugs are small, 5-6 mm long, dorso-ventrallytables and even under the table spreads, rear of sinks, meat flattened, wingless, dark brown insects. The nasty pungentsafes and other harbourage areas. Use of 2-5% dust or 1-3% odour which this group emanates is because of the presencesolution or emulsion of Organophosphorous compounds like of stink glands. Metamorphosis is incomplete with presenceMalathion or Carbamate insecticide such as Propoxur gives of egg stage & 4 nymphal stages. Females lay flask shaped,excellent results. To obtain a quick effect in heavy infestations operculated eggs singly in hidden sites. It takes 4 to 6 weeks foror to drive them out from the hiding places, a direct spray the development from egg stage to adult. Bugs can stay withoutcontaining 0.3% Pyrethrum or 0.5 to 1.0% DDVP or Fenitrothion food for months & can travel long distances through travelingmay be used. Small pills of flour containing boric powder left on bags, laundry, furniture, bedding, old charpoys, soiled clothingdining table, food safes and pantry boards or under table cloth etc. Bugs so far have not been incriminated for any humanalso kill cockroaches. Abermectin and Synthetic pyrethroids disease; though have been suspected for transmitting diseases.(Table - 1) are currently being used for control. Newer Infestation though can cause insomnia, pruritis, dermatitisinsecticides, Fipronil and Imidacloprid Gel have been found to etc. Prevention includes maintenance of hygiene, thoroughbe very effective in controlling cockroaches. Fipronil has been check of furniture & belongings. Insecticides viz. Malathiondemonstrated to have “cascade effect” (secondary killing of @2% or Chlorpyrifos @0.5% etc. may be used. Disinfestationscockroaches due to necrophagy amongst them, whereby they of blankets, beddings, mattresses and mosquito nets may beconsume Fipronil killed cockroaches and get killed in turn). carried out. Debugging can be used for treatment of the cotsIt is important to remember that chemical control gives only (charpoy).temporary results and maximum efforts should be made to Cockroaches are one of the most annoying pests encounteredimprove the environmental sanitation and housing conditions. in an urban area. The common domestic species are BlatellaMoreover, there are reports that the German cockroach has germanica (infest buildings), Periplaneta americana & Blattabecome resistant to several Organo-chlorine, Organo-phosphate, orientalis. Cockroaches are dorso-ventrally flattened withCarbamate & Pyrethroid insecticides. The insecticides used for colour varying from dark brown to black. They breed in warmcockroach control are summarised in Table -1. moist places (humid microclimate of the kitchen), laying eggs in cracks, crevices and sinks. Feed on any material meant for Table - 1 : Insecticides for Cockroach control human consumption, their mouth parts are adapted for biting Insecticide Concentration Use & chewing. They destroy food, damage fabrics, books and Baits/ sprinkle other household articles. Cockroaches spread diseases like Boric acid 100% cholera, typhoid, dysentery, protozoal cysts, intestinal worms along corners etc. by polluting food with infective material carried on their Imidacloprid Gel 1.85 - 2.15% Cracks and crevices legs and bodies. Prevention comprises of good housekeeping, Cracks and crevices filling up of all cracks & crevices. Infestation can be controlled Fipronil Gel 0.01 - 0.03% with insecticidal sprays (Malathion or Propoxur), dusts or Has a cascade effect baits. Spray containing 0.3% Pyrethrum or 0.5 to 1.0% DDVP Fenitrothion 1 - 2% Spray brings about quick effect. Newer insecticides, Fipronil and Malathion 3% Spray Imidacloprid have been found to be very effective in controlling Cyphenothrin 0.5% Spray cockroaches. Deltamethrin 0.03% Spray • 951 •
  • 52. Study Exercises Fill in the BlanksMCQs & Exercises 5) Simulium flies are known vectors of _______________ 6) Nasty, pungent or offensive odour associated with bugs1) Cimex lectularius & C rotundatus consist of two important due to the presence of _______________ families of (a) Simulium flies (b) Bugs (c) Cockroaches 7) _______________ gel is an effective insecticide against (d) None. cockroaches and has a cascade effect.2) Which of the following in relation to bugs is not correct (a) Head bears antennae (b) Pair of well developed eyes True or False (c) 5 nymphal stages (d) Flask shaped operculated eggs. 8) Black flies are black in colour.3) Prevention & control of bed bugs can be achieved by 9) A female bed bug lays 2 to 10 eggs a day with a total up to all except (a) Malathion @2% (b) Chlorpyrifos @ 0.5% 200 to 300 in her life time of 6 to 8 months. (c) Debugging of bed stands (d) Fipronil Gel. 10) The mouth parts in cockroaches are adapted for biting and4) Sticky traps and Visual assessment method are used for chewing. surveillance of (a) Bed bugs (b) Cockroaches (c) Simulium Answers : (1) b; (2) c; (3) d; (4) b; (5) Onchocerciasis; (6) Stink (d) All of these. glands; (7) Fipronil; (8) False; (9) True; (10) True. formic acid. It is, however, much more painful, and if sufficient 162 Envenomizing Pests poison has been injected, may cause distressing symptoms which may take twenty four hours to pass off. Stings of red scorpion (Mesobuthus tamulus) can be serious with massive Rina Tilak release of catecholamines, producing raised BP arrhythmias, , cardiac failure and pulmonary oedema. Profuse sweating,Scorpions dilated pupils and priapism can occur.Scorpions are one of the commonly encountered venomousarthropods of the class Arachnida (Fig. - 1). At least 1000 Box - 1 : Prevention of Scorpion Stingspecies of scorpions have been described, but only 20 species Do not encroach their hiding places especially if ill equippedare of medical importance. The last segment of their bodies is (i.e. barefoot or wearing loose / open sandals in areas withmodified to form a flexible tail, with a vesicle holding poison loose stones, fallen debris etc.)gland and a sharp spine. They vary in size from about 2 to Scorpions are active at nights. Always carry a torch while20 cm and are cryptozoic and nocturnal, spending the day moving in infested areas at night.concealed under stones or fallen tree branches or in burrowsand venturing out after sunset in search of food. The common Erect barrier up to 20 cm by means of tiles at the base ofIndian species belongs to the genera Buthus (Mesobuthus) and walls and steps to prevent scorpion encroachment.Palamnoeus; the former are more poisonous. Fill cracks and crevices to deny hiding places. In infested areas, people should sleep with mosquito nets Fig. - 1 : Scorpion properly tucked. It is advisable to use treated bed nets. Clear all junk and rubbish from around the house. Shake the shoes / clothes well before putting them on. Lastly use chemicals if problem still remains unresolved. A Scorpion sting case needs immediate medical attention. A local anaesthetic (1% Lignocaine) at the site of sting or a strong oral pain killer is advised. For stings with less pain, ice therapy works well. There is no commercially available antivenin for treatment of Mesobuthus tamulus stings in India. The effects are more marked in children, it is, however, very rare that a fatal doseScorpion sting as a rule is not more dangerous than bee or of the venom is injected. If the sting is on the extremities, anwasp sting as the chemical nature of the poison is similar to immediate ligature may be helpful. Application of a strong • 952 •
  • 53. solution of ammonia relieves pain in a majority of cases; a series reaction (usually swelling, erythema and lymphangitis;of injections of 1% Novocaine or Lignocaine and Adrenaline dizziness, nausea and anxiety are occasionally described andat the spot and along the nerve may be necessary in others. rhabdomyolysis and renal failure have also been reported).Barbiturates in large doses are useful in reducing restlessness. Solution of ammonia is useful for local application and in bitesPatients developing priapism, dilated pupils, sweating and of the larger centipedes morphia may be necessary to allay thebradycardia may require early energetic treatment with pain. 2-4% Malathion as spot application is very useful.vasodilators. Preventive measures include alertness in avoidingcontact with scorpions in infested areas, putting on clothes Leechesand shoes after shaking them well and proper housekeeping. Leeches (Hirudinea) are a class of annelid worms that attach toPropoxur 2% or Chlorpyrifos @ 0.2-0.5% may be used. Synthetic their hosts with chitinous cutting jaws and draw blood throughpyrethroids are generally not used as they irritate the scorpions muscular suckers. They are particularly troublesome nearand risk is increased further. streams and rivers, in leafy forests and marshy jungles.Ants The two important species are:Ants are common annoying insects. They have also been ●● Haemadipsa zeylanica, which is a small land leech, aboutexperimentally incriminated in the mechanical transmission 2.5 cm long with great power of penetration into theof excremental infections. They should therefore be kept away interstices of clothing, putties or laced boots. They oftenfrom foodstuffs by placing the legs of food safes, tables etc. drop from tree leaves onto man or animals passing by andin anti-formicas viz. bowls or tins containing water or waste suck blood.crude oil. Insecticidal sprays like Pyrethrum or Malathion are ●● The other variety is Limnatis nilotica - the large aquaticeffective. Ordinarily, the ant-bite causes only a sharp stinging; leech which on being ingested, fastens itself to the mucusthe bites of some of the larger ants may be very painful involving lining of the mouth, pharynx, larynx or nasal cavitiesfaintness and shivering. Dilute ammonia or any other alkaline of man or animal producing prolonged bleeding unlesssolution applied relieves the pain. removed. Leech bites are painless but the bleeding may be prolonged (after the leech has detached) due to a powerfulBees, Wasps and Hornets anti-coagulant, hirudinin, present in its saliva.In bees and wasps, venom is produced in glands at the Gum boots or jungle boots are very effective in protectingposterior end of the abdomen and is expelled by contraction from leech bite. A frequent search of the body for the presenceof muscles of the venom sac, which has a capacity of up to of leeches should be made. The leech should not be dragged0.1 ml. Uncomplicated stings cause immediate pain, a wheal- or pulled off the skin because of the risk of breaking andand-flare reaction and local edema and swelling that subside leaving behind its suction apparatus which is liable to causein a few hours. In sensitized individuals there may be alarming inflammation and suppuration. Salt, vinegar or a tobaccosymptoms. infusion application or a touch of the lighted end of a cigaretteHoneybees often lose their stinging apparatus and the attached induces the leech to relinquish its hold; tincture of iodinevenom sac in the act of stinging and subsequently die, it should should be applied to the bitten spot and a piece of adhesivebe removed gently by pulling it out, care being taken not to plaster may be applied on it. Internally attached leeches maysqueeze the venom in the wound. The site should be cleansed detach on exposure to gargled saline or may be removed byand disinfected and ice packs applied to slow the spread of forceps. Repellents DEET & DEPA can be used to providevenom. Elevation of the affected site and administration of protection. The repellents can be applied on to the clothing asanalgesics, oral antihistamines and topical calamine lotion well as topically over the skin. At night a properly adjustedrelieve symptoms. Local application of an alkaline solution of mosquito net, preferably insecticide treated bed net providessodium bicarbonate or ammonia or soap and applying pressure good protection. Aquatic leeches can be removed from drinkingwith a moistened piece of lint are useful in relieving pain. water by filtering through a sieve or a piece of muslin.Papain diluted roughly 1:5 with tap water is said to produce Spidersimmediate relief of pain. Disturbing the honey-comb may bring There are more than 30,000 recognized species of spiders,the whole swarm on the person responsible or any one who however, only about 100 can defend themselves aggressivelyhappens to be in the vicinity. Their stings may cause serious and have fangs sufficiently long to penetrate human skin. Theallergic symptoms requiring adrenaline and/or morphine true spiders (Arachnida) have poison glands and inject venomadministration. Wasp’s nests should not be destroyed in the into their prey. The common species of spiders as a rule do notdaytime; they are generally destroyed at night when all wasps bite man. If by chance it happens to bite, the bite amounts toare inside. Insecticidal treatment includes use of 1% Dichlorvos, no more than a pin prick. Envenomations of the brown or fiddle0.015% Deltamethrin or 0.5% Chlorpyrifos. spiders (Loxosceles species) and widow spiders (LatrodectusCentipedes species) may be life-threatening. Some spiders, especially thoseCentipedes (Myriapoda) possess a pair of legs to each apparent belonging to the genus Latrodectus produce severe effects insegment of the body; the first pair is modified to form poison man. Important species are L hasselti, the ‘red-backed’ spiderclaws. The bites of small centipedes’ gives rise to mild local and L mactans the black widow and the allied species. Theinflammation but the larger centipede Scolopendra gigantia acute symptoms generally subside after a few days, but painmay cause a severe painful bite with marked local and general may persist for some time. In Latrodectus bites, the death rate • 953 •
  • 54. may amount to 6% or higher. Centipedes possess a pair of legs on each segment of the body.Identification of the offending spider should be attempted, Bites can cause mild reaction to severe pain. Ammonia andboth because specific treatments exist for bites of spiders. Morphine is used for treatment.Initial management includes local cleansing, application of Leeches are a class of Annelid worms; the two importantsterile dressings and cold compresses, and elevation and loose species are the land leech & the aquatic leech. Leech bites areimmobilization of the affected limb. Analgesics, antihistamines, painless but bleeding may be prolonged due to presence of antiantibiotics, and tetanus prophylaxis should be administered -coagulant. Ideally, leech should not be dragged or pulled offif indicated. Use of sedative is contraindicated. Intra venous the skin. Prevention is by wearing gum boots and searchingadministration of widely available equine antivenom rapidly the body for leeches. DEET & DEPA can be used to providerelieves pain and can be life-saving. Because of the risk of protection.anaphylaxis and serum sickness, antivenom should be reserved The true spiders (Arachnida) have poison glands. Importantfor severe cases involving respiratory arrest, uncontrollable species are the red backed spider & black widow spider.hypertension, seizures, or pregnancy. Intravenous Calcium Treatment of a bite is immediate washing and ligation. Aspiringluconate or Magnesium sulphate also gives dramatic relief or morphine is used for pain relief. Intravenous Calciumto cramps. Spot (Infested area) treatment with 3% Malathion, gluconate or Magnesium sulphate gives relief from cramps.0.03% Deltamethrin, Chlorpyrifos @ 0.2-0.5% has been foundto be effective against spiders. Study Exercises MCQs & ExercisesSummary 1) Buthus (Mesobuthus) and Palamnoeus are common IndianScorpions are one of the commonly encountered venomous species of (a) spiders (b) scorpions (c) bugs (d) fliesarthropods of the class Arachnida. The common Indian species 2) Hypertension, arrhythmia, cardiac failure and pulmonarybelongs to the genera Buthus (Mesobuthus) and Palamnoeus. oedema may be encountered following stings ofScorpion sting (chemically similar to formic acid) is much more (a) Scorpion (b) Spider (c) Wasps (d) All of thesepainful than bee or wasp sting, though not more dangerous. 3) Scorpion sting can be treated by (a) AmmoniaHypertension, arrhythmia, cardiac failure and pulmonary (b) Lignocaine (c) Barbiturates (d) Alloedema may be encountered following stings of Mesobuthus 4) This should not be used to treat stings of bees, waspstamulus (Red scorpion). Prevention includes avoiding hiding & hornets (a) Magnesium sulphate (b) Adrenalineplace of scorpions especially when ill equipped, erecting barriers (c) Morphine (d) Papain& filling up of cracks & crevices. There is no commercially 5) Scolopendra gigantia is a species of (a) Spider (b) Scorpionavailable antivenin for treatment of Mesobuthus tumulus. (c) Centipede (d) NoneApplication of a strong solution of ammonia relieves pain in Fill in the Blanksa majority of cases; in others, injections of 1% Novocaine orLignocaine and Adrenaline bring relief. Preventive measures 6) Stings of red scorpion can be serious due to release ofinclude alertness in avoiding contact. Propoxur 2% or __________Chlorpyrifos @ 0.2-0.5% may be used. 7) Class of annelid worms which suck blood, cause painful bites __________Ants are common annoying insects; need to be kept away from True or Falsefood stuffs. Ants have been involved in mechanical transmissionof diseases & their bites may sometimes also be very painful. 8) Erecting a barrier up to 20 cm by means of tiles at the baseDilute ammonia relieves pain. Other means of prevention are of walls to prevent scorpion encroachment.use of anti-formicas & Pyrethrum or Malathion spray. 9) Stings of Bees, Wasps & Hornets should not be removed. Answers : (1) b; (2) a; (3) d; (4) a; (5) c; (6) Catecholamines;Bee, Wasps & Hornet stings are often painful, the honey bee (7) Leeches; (8) True; (9) False.often leaves sting along with poison gland in the puncture, thisshould be promptly removed and pain relief may be obtained by Further Suggested Readingapplying alkaline solution of sodium bicarbonate or ammonia. 1. Anthony S. Fauci, Eugene Braunwald, Harrison’s, Principles of InternalInsecticides which can be used are Dichlorvos & Deltamethrin. Medicine, Seventeenth Edition, 2008, Volume 2 ISBN 978-0-07-147693-5, the McGraw-Hill Companies, United States of America. • 954 •
  • 55. required for full development of a tick is from six weeks to 163 Ticks and Mites 2 years. Fully engorged fertilized female drops off to the ground and lays eggs in cracks and crevices in the soil under stones or among roots of shrubs and grass and such other Rina Tilak sheltered spots. Hard ticks deposit all their eggs in a single act of oviposition after which they die. Eggs take a few weeksTicks and mites belong to class Arachnida, which are to several months to hatch. Larvae are six legged and do notcharacterized by the presence of two distinct body parts - feed for about a week after emergence. Thereafter, they becomecephalothorax and abdomen and four pairs of legs. Antennae hungry and active and climb on vegetation for attachment toare absent and eyes may or may not be present. Metamorphosis passing hosts (this is called questing). They feed for aboutis incomplete and the adults resemble the nymphs except for three days and drop off when engorged and remain quiescentthe fact that nymphs lack genital aperture while in the adult for digestion of blood. After the first moulting, the nymphsthe sexes are distinct. The larvae are morphologically distinct emerge with their fourth pair of legs and seek a new host inwith three pairs of legs. the same manner as the larvae, feed and again drop off. TheyTicks again moult and become sexually mature. The adults are also parasitic and exhibit questing. Copulation takes place after theTaxonomy & Morphology last moult and the male dies after fertilizing the female. TheTicks belong to the super-family Ixodoidea. They are female engorges and then deposits eggs.distinguished from other acarines by their relatively large sizeand absence of prominent hairs on the body. They are oval in Fig. - 2 : Soft Tick Dorsal and Ventral Aspectshape and of varying colours and dorsoventrally compressed.Females are larger than males and are capable of greatdistention. Both sexes as well as the other stages i.e. nymphsand larvae thrive on blood alone and lead an intermittentparasitic life during a major part of their life cycle. They arefree living on the ground in between various moults duringdevelopment. There are two families, Family Ixodidae which isthe hard tick and Family Argasidae which is the soft tick. Thehard tick is more a jungle tick while the soft tick is a domesticor household tick like a bedbug.Ixodidae or Hard TicksThe dorsum of the adult male is covered by a dark shield, like Bionomicsthat of the tortoise, called the scutum. This may be ornate withgrey or white ‘patterns’. In females and immature males, it Hard ticks are open jungle dwellers and thrive on animalcovers only the anterior part behind ‘the capitulum’ which is hosts; hence they do not attach themselves to humanthe false head, actually formed by the mouthparts anteriorly beings voluntarily, except when a person comes across themand therefore visible from above (Fig. - 1). accidentally. Argasidae (soft ticks), on the other hand, although preferentially parasitic on animals and birds attack man voluntarily. These are found in human dwellings and cattle Fig. - 1 : Hard Tick - Dorsal and Ventral Aspect sheds and attack man and animals during their sleep. They however, live away from their hosts, like bedbugs, in cracks and crevices and only emerge at night to feed on the host. Ticks can survive starvation for a long time. Vector Potential Ticks produce diseases in man by transmitting the viruses, rickettsiae, spirochaetes and bacilli of infectious diseases and through toxin present in their saliva. Some of the factors which account for high vector potential are that all the stages are essentially haematophagous and are persistent blood suckers and while feeding they attach firmly and cannot beArgasidae or Soft Ticks easily removed. They are resistant to varying environmentalThese are oval with leathery cuticle and devoid of scutum. conditions and relatively protected from natural enemies.Their mouth parts are placed ventrally and hence not visible The trans-stadial and transovarian transmission of infectionfrom above and they possess no festoons (Fig. - 2). helps in maintaining infection for several years. Ticks have the power to regenerate lost parts such as amputated legs and alsoLife History the ability to repair mutilated mouth parts, which conservesAll species of ticks pass through four stages during their them for long.development viz. egg, larva, nymph and adult. The total period • 955 •
  • 56. Soft Ticks cusps or on rumps of rats, mice, shrews, bandicoots and otherSoft ticks of the genus Ornithodorus transmit various types of small mammals, reptiles and birds in orange coloured clustersspirochaetae causing relapsing fevers in certain parts of the of as many as 50 to 200 larvae. A cluster of 5 to 6 larvae is asworld. O moubata is the vector of Borrelia duttoni in Africa; big as a pin-head. When the cluster detaches, a scab is formedO lahorensis has a very wide distribution in Central Asia and showing an evidence of recent infestation.North West India. In India, they are found in Kashmir and areknown as O crossi. Fig. - 3 : Trombiculid Mite (Adult)Hard TicksThese are much more ubiquitous and produce larger varietiesof human diseases. The most important of all are the variousrickettsial infections transmitted by the hard ticks of thegenera Ixodes, Dermacentor, Amblyomma, Haemaphysalis,Rhipicephalus, Hylomma and Boophilus. Viruses causingKyasanur Forest Disease, Colorado tick fever and otherHaemorrhagic fevers and Encephalitides are transmitted.These also transmit P tularensis, the causative organismof Tularaemia. Tick paralysis is an acute ascending flaccidparalysis due to an unknown toxin the tick’s saliva introducesthrough the bite of certain species of ticks of the generaDermacentor, Ixodes and Amblyomma. It affects mostly childrenand young domestic animals in Australia, South Africa, NorthAmerica, Southern U.S.A. and N.W. Pacific. Even a single tickbite may cause fatal paralysis. In certain cases, reaction from Life Historyimproper or partial removal of ticks or due to the bite itself maycause itching, swelling and ulceration at the site of the bite. The stages in the life history of a mite are egg, larva, nymphOtoacarisis is an invasion of the auditory canal by ticks. and adult. The eggs are laid singly on the surface of the soil. The larva leaves the egg-shell and becomes very active. MovingMites quickly over the surface of the soil and low lying vegetation,The vector mites belong to the order Acarina and family it seeks a suitable host such as rat, mouse, bandicoot andTrombiculidae which comprises many hundreds of species of shrew and so on. While feeding, it buries the whole length ofworld wide distribution. They are found in great abundance in its chelicerae in the host’s skin and injects an irritant secretionareas with hot, humid climate, thick vegetation and presence of which causes tissue lysis. The larva feeds on the lymph and thesmall vertebrates like rodents. The foothills in subtropical and tissue fluid but not on blood of the host. The orange red colourtemperate regions offer them ideal conditions. In the tropics, of the larva is therefore not due to ingested blood. The larvaethey are found even at heights in mountain valleys. These feed for 2 to 3 days and then drop off to the ground concealinghave also been found in the Alpine-subarctic terrain in the themselves in loose soil, and here they develop into nymphsHimalayas as well as at the level of coniferous forest-glacial and finally into adults. Generally, it takes 6 to 12 weeks for itsvalleys in Pakistan. They are known by various names such development from egg to adult stage. Only the larval stages areas chiggers, harvest mites, kedany or scrub mite. Important parasitic; the nymphs and adults are never parasitic and feedspecies of the genus Leptotrombidium are akamushi which is on small insects in the soil or their eggs.distributed widely in Japan, South East China, Korea, Malaysia Bionomicsand Philippines and L deliense which is vastly distributed in the The mites are distributed in areas ideal for their survivaltropical regions of South East Asia, Indian sub-continent, Sri called as “Mite Islands”. Mite Islands are patches of groundLanka and Maldive Islands. In India, it is present in the whole characterized by thick vegetation cover, mainly the scrub junglesof the Shivalik range from Kashmir to Assam, the Eastern half or other tall grasses offering protection from direct sunraysof the plains adjoining the foothill ranges, the Eastern and and desiccation, nearly 100% relative humidity at ground levelWestern ghats and the Vindhyachal range in Central India. and ideal ambient temperature of 27± 5°C. Such conditionsMorphology also provide sanctuaries for small vertebrate life such as rats,The adult is about 3-4mm in size, is densely covered with hair mice, bandicoots, and shrews which are hosts for larval mitesand has a figure of eight (Fig. - 3). The mouth parts consist (shrews are considered as the index animal for scrub typhus).of a pair of chelicerae and a pair of palps, together giving the These animals are also the reservoirs of rickettsiae for whichmite an appearance of having a false head. The adult resembles the trombiculid mites are vectors. Hence, these mite islandsthe nymph except that it is larger and more densely covered may also become typhus endemic foci. Mites are most activewith hairs; ‘Kedany’ meaning hair in Japanese language. The during the whole rainy season and their prevalence in such mitelarva is pale yellow to orange-red in colour with a circular body islands is related to the intensity and length of the monsoons.bearing three pairs of legs and branched hairs on the body In dry season, the adults migrate deeper into the soil, the eggand on the legs. They are found in nature in the interior of ear laying ceases and the mite islands shrink; during monsoon, • 956 •
  • 57. there is prolific activity and the mite islands expand. Patchy of active ingredient (a.i.) per hectare of ground surface area, ordistribution of mite islands and their selective choice of locality else “Cyfluthrin EC” applied in dosage of 0.1 Kg (100 grams) ofexplain the patchy nature of typhus endemic foci. The typical active ingredient per hectare. Malathion 5% may also be usedterrains favourable for the mites to thrive and propagate are (4 Kg of active ingredient of malathion will be present in 8 litresas under : of 50% EC commercial supply; this 8 litres will be mixed with●● Man-made rural and urban wastelands like overgrown 72 litres of water to get 80 litres of 5% solution which should clearings produced by shifting cultivations. then be sprayed over one hectare of ground surface area).●● Domestic sub-urban waste lands produced around neglected b. On Vegetation : In areas where vegetation cannot be patches in and around villages and even big towns, such as removed for various reasons, control of ticks on vegetation can neglected gardens and plantations or overgrown clearings be achieved by insecticide dusting or spraying from the ground therein; deserted villages are heavily infested. or air at the dosage varying from 0.5 to 2 Kg/hectare. In woody●● Around the edges of moist depressions, water meadows, and bushy areas, the dosage is increased proportionately. grassy but not swampy river banks and moist sites such Malathion, Fenthion, Propoxur and Permethrin are suitable. as seepages along over ground canal areas. c. Premises : Against soft ticks, application of insecticide to●● The hedgerow types of features ranging from a simple floors and walls of infested premises on alternate days after bushy hedgerow to belts of forests following water courses initial scraping and scorching are necessary. Treatment for 2 and ravines which are commonly left in deforested areas in weeks before occupation gives good control. During this period and below the foothills. sweeping of floors should be discontinued. Such a series of●● The scrub at the outskirts of the forests and low lying applications repeated 6 weeks afterwards gives adequate patches overgrown with elephant grass in sunny clearings protection to people staying in such habitations as camps inside thick forests. during disasters or migratory labour camps, etc. The insecticidesVector Potential should also be applied to beds, mattresses, rugs and furniture. InLarval mites belonging to several genera attack man but known tick infested areas, particularly where there is a historyonly the Genus Leptotrombidium contains species of medical of relapsing fever, infested houses/ areas should be avoided asimportance. In India, Leptotrombidium deliense is the vector far as possible. Organophosphorus compounds like Malathionof Orientia tsutsugamushi causing Scrub typhus; in Japan, and Fenitrothion or Carbamate compounds like Propoxur canthe closely related variety L akamushi (kedani mite) transmits be used either as 0.5 to 1.0% spray or as 5 to 10% dust.Scrub typhus. Rickettsiae taken up by larvae while feeding on d. Domestic Animals : Dogs and other domestic animals canrodents are carried through its nymph, adult stages and then be freed of ticks by a wash or spray containing 2% Malathion,its eggs (trans-stadial transmission). The larvae hatching 1% Propoxur, Deltamethrin (0.025%) etc. Only half theseout of these infected eggs are capable of transmitting the concentrations should be used if the animal is to be dipped andrickettsiae to the next host. The infection is thus trans-ovarially the entire animal should be immersed except the head. Duststransmitted for some generations and hence the mite also acts containing 5% Malathion, Propoxur (1%), Cyfluthrin (0.1%),as a reservoir of infection. Larvae feed only once during their Deltamethrin (0.05%), Temephos (2%), Fenthion (2%) etc. maylife time. Therefore, transmission of infection occurs in second also be used. The premises which animals visit or is tied in,or subsequent generations. When a larva lying on the ground should also be treated.comes in contact with a human being (instead of a rodent as B. Personal Protectionwould happen in the normal course), it attaches on to him and a. The repellant materials used for personal protectionfeeds on his lymph; in the process, the rickettsiae contained in against ticks and mites are Dibutyl-phthlate (DBP), Diethylthe mouth parts are injected into the lymph of the human being phenyl acetamide (DEPA) and Diethyltoluamide (DEET).thereby causing scrub typhus. These are more effective when applied to the clothing thanControl of Ticks and Mites to the skin. The effect may last for nearly six washings orA. Insecticidal Control weeks which ever is earlier. However, if it is ironed, thea. Area Treatment : This is the only reliable Acarine control concentration falls below effective limits. DEET/ DEPA maymethod in camp sited areas or areas amenable for such be used for application on the exposed parts of the body totreatments. Before the application of an insecticide to the reinforce the use of protective clothing treated with DEET/areas infested with hard ticks and mites, clearing of bushes by DBP/DEPA when working in an uncontrolled area or undercutting them is advantageous. If possible a bulldozer should be acute emergency when application of repellent on theemployed. When the top soil is bare and dry, an area becomes clothing prior to entry in an unknown or uncontrolled areaconsiderably safe and more suitable for insecticidal action. is absolutely impossible. The persistence of DEPA on clothesInitial coverage of the area should be thorough. It may require post ironing is superior to that of DEET, whereas both arerepetition after 8 weeks and occasionally a third time during equally effective when applied topically. Permethrin maythe hot-humid season. If people have to go to some nearby also be used for treatment of clothing.stream for bathing or washing their clothes, the selected area b. Wearing shirts with rolled down sleeves tightly buttonedshould be similarly treated as the stream edges covered with at the cuffs, the lower ends of trousers tucked in socksvegetation are favourite sites for acarines. “Malathion 50% EC” and wearing of proper boots considerably reduces the risk(as 5% solution) should be sprayed in a dosage of 4 kilograms against ticks and mites. • 957 •
  • 58. c. Clothes for drying should be hung on ropes especially fixed insecticide treatment is undertaken, the degree of risk should for the purpose and not on the vegetation. Bush and grass be assessed by determining the prevalence of adult and larval on the periphery of a camp becomes infested by larval mites Acari. and ticks brought in by the rats migrating into the camp. (a) Mite Survey : Superficial layers of earth are scraped from Therefore, purposeless wandering in such areas should be moist areas around the roots of scrub and mixed with water discouraged. in a bowl. Adult mites resembling a figure of 8 float in a fewd. More mites and ticks are picked up by standing or sitting minutes. For non parasitic larvae, pieces of dark cardboard are than by walking over the infested ground. Therefore, while placed edge wise forming tent fashion structures on the ground in such areas it is unsafe to lie down on a grassy ground. at intervals, larvae crawl up the cardboard and congregate The immediate vicinity of a tree base should be avoided for at its top edge within a few minutes. Rats caught from the resting, so also the green edges of a stream or an irrigation area should be examined for the clusters of larvae or scabs channel. Open grassy grounds should be avoided in tick in ear-cusps and shrews for clusters on their rumps. If the infested areas. ears or rump is infested, they should be carefully cut with finee. Before retiring at night or after leaving a tick infested area scissors and placed in 70% alcohol vials. Rodent trapping is one should take a bath and carefully search one’s body and done in field (Camps, fringe areas) by specialized traps called clothing for presence of ticks. If a tick is found attached to Sherman traps, whereas in peri-domestic areas, Wonder traps the body it should be removed immediately, because every may also be used. The trapping procedure is described in a added moment of its attachment increases the danger of subsequent chapter on rodents. Once the traps are brought to transmission of infection. Pulling of a tick has the danger the laboratory, the rats are transferred in to large polythene of breaking off its parts, therefore, it should be removed bags, anaesthetized and thereafter ectoparasite screening is by making the surrounding skin taut, slipping the point undertaken. While carrying out the survey, one must protect of a flat needle or a scalpel under the mouth parts and oneself adequately with protective clothing and repellents. then removing the mouth parts by raising the point of the As a rough guide, it can be said that the Scrub typhus risk in needle with a minimum of tissue damage. Iodine or any any area during the monsoon is considered low if only up to other antiseptic should then be applied to the site. 10% of the rats have been found infested on consecutive twof. Use of Insecticide treated mosquito net gives some surveys unless cases have occurred already; if 20-40% of rats protection against soft ticks. have been found infested the contraction of infection is veryC. Habitat Management : Vegetation management is another probable; and if 50% or more rats have been found infested thecontrol option for ticks. Removal of shrubs, trees, or tall risk is high and the site should be considered as dangerous.grass can be useful in recreational areas. Wherever this is not Similarly, even if a single rat is found infested with more thanpossible, area treatment with insecticide may be the only viable 100 larval mites, the area should be avoided, being a very highoption. risk area.Anti-Rodent Measures (b) Tick-Survey : Ticks are collected by sweeping flags madePersistent anti-rat hygiene is of great value in reducing the of white flannel across the vegetation (Flagging/draggingrisk of diseases conveyed to man through ticks and mites. method). The larvae, nymphs and adults get attached to themThe main objective should be to reduce ingress of rodents by and are easily detected against the white background of theproper disposal of camp and kitchen refuse and removal of flag. They should be picked up by forceps and placed in 70%overgrown vegetation and rubble which afford them shelter. alcohol vials. Parasitic stages of ticks on various animals canRat destruction requires forethought; because if the feeding be collected by catching rodents, shrews and other animals.of larval ticks and mites is interrupted by the death of rodent Physical examination of a volunteer for ticks attached on hishosts, a number of released acarines may reattach themselves body after he has travelled for a stipulated / fixed period ofto another host, which may be man. Active rat destruction time in an area delineated for survey also provides informationmay be adopted when the first infestation is at its peak i.e. a on tick presence/ abundance. Dry ice traps are one of the mostmonth or so after the rain starts. It is better to trap and then effective means of sampling ticks.destroy them so that their parasites do not escape. When deadrats are collected from any endemic foci, the soil under and Summaryimmediately around them should be treated with insecticide. Ticks and mites belong to class Arachnida; body is divided intoSoft tick control is further achieved by rat-and-tick-proofing cephalothorax & abdomen with 4 pairs of legs. Ticks belong toof dwellings. All cracks and crevices, fissures and other points two families : Ixodoidea (hard tick) and Argasidae (soft tick).of ingress should be closed and all doors should be made tight All stages thrive on blood & lead an intermittent parasitic life.fitting to keep away rodents. Dorsum of hard tick is covered by scutum which is replacedCamp Siting by the leathery cuticle in soft ticks. All species of ticks pass through 4 stages - egg, larva, nymph & adult. Eggs are laid inIn civil life, camps may need to be sited for temporary cracks & crevices. Hard ticks deposit all their eggs in a single actsettlements of labour population when large industrial / of oviposition, after which they die. Larvae are six legged andurbanization projects are being launched in possibly infested do not feed for about a week, thereafter they attach to passingareas or during disaster like situations. Before any area in hosts. They feed on blood & drop off. The nymphs and adultsthe known endemic tract is selected for camping or before the (both sexes) are parasitic and exhibit questing. Male dies after • 958 •
  • 59. fertilizing the female. Hard ticks thrive on animal hosts & soft Study Exercisesticks attack man voluntarily. Ticks produce diseases in man MCQs & Exercisesby transmitting viruses, rickettsiae, spirochaetes and bacilli ofinfectious diseases. Rickettsial infections are transmitted by 1) Which of these regarding ticks is not true (a) Females arethe hard ticks of the genera Ixodes, Dermacentor, Amblyomma, larger than males (b) Both sexes thrive on blood aloneHaemaphysalis, Rhipicephalus, Hylomma and Boophilus. Hard (c) They are free living on the ground in between variousticks also transmit virus causing KFD and P tularensis, the moults (d)All are true.causative organism of Tularaemia. Soft ticks transmit various 2) Soft ticks are involved in transmission of which of thesetypes of spirochaetes causing relapsing fever. (a) Relapsing fever (b) Kyasanur forest disease (c) Tick paralysis (d) Tularaemia.The vector mites belong to the order Acarina, family 3) Mite island is an area having (a) 100% relative humidityTrombiculidae. Found in great abundance in areas with (b) Temperature of 27± 5°C (c) Scrub jungles or other tallhot, humid climate, thick vegetation and presence of small grasses (d) Rats, mice, bandicoots, and shrews (e )All ofvertebrates like rodents (Mite Island). They are known by various thesenames such as chiggers, harvest mites, Kedany or scrub mite. 4) Which is the parasitic stage in mites (a) Egg (b) LarvaImportant species of the genus Leptotrombidium are akamushi (c) Nymph (d) Adultsand deliense. They possess a figure of eight shaped body with Fill in the Blankseight legs. They are found in nature in the interior of ear cuspsor on rumps of rats, mice, shrews, bandicoots and other small 5) Ticks & mites belong to the class _____________mammals. The stages in the life history of a mite are egg, larva, 6) Hard ticks deposit all their eggs in a single act ofnymph and adult. The eggs are laid singly. The larva seeks a ____________ after which they die.suitable host such as rat, mouse, bandicoot or shrew and feeds 7) The most important vector species of trombiculid miteon the lymph and tissue fluid. Mites are vectors for various transmitting scrub typhus is __________rickettsial diseases. Leptotrombidium deliense transmits 8) The most effective means of sampling ticks is __________Orientia tsutsugamushi causing Scrub typhus. True or falseControl of ticks & mites can be achieved by clearing of bushes 9) Hard ticks belong to Family Ixodidae and soft tick to Familyin areas infested by ticks & mites followed by application Argasidae.of insecticides. Malathion 50% EC (@ 5% solution) should 10) The total period required for full development of a tick isbe sprayed in a dosage of 4 kg of active ingredient (a.i.) per from six weeks to 2 years.hectare. In areas where vegetation cannot be removed, dusting 11) Copulation in case of ticks takes place after the last moultcan be done by Malathion or Fenthion. Insecticides should & the male dies after fertilizing the female.also be applied to beds, mattresses, rugs and furniture. Dogs 12) The mite larva feeds on lymph and the tissue fluid but notand other domestic animals can be freed of ticks by a wash or on blood.spray containing 2% Malathion or 1% Propoxur. The repellants 13) Only the adult stages of ticks are parasitic, whereas theused for personal protection against ticks and mites are larvae and nymph feed on plant juice.Dibutyl-phthlate (DBP), Diethyl phenyl acetamide (DEPA) and Answers : (1) d; (2) a; (3) e; (4) b; (5)Arachnida; (6) Oviposition;Diethyltoluamide (DEET). Clothes for drying should be hung on (7) Leptotrombidium deliense; (8) Dry ice collection; (9) True;ropes. Before retiring at night or after leaving a tick infested (10) True; (11) True; (12) True; (13) False.area, one should take a bath and carefully search one’s body Suggested readingand clothing for presence of ticks. Anti rodent measures like 1. Schuster R, Murphy PW, editors. The Acari : Reproduction, Development andproper disposal of refuse & removal of overgrown vegetation Life History Strategies. London : Chapman and Hall, 1991.helps in reducing the risk of diseases conveyed to man through 2. Evans GO. Principles of Acaralogy. Wallingford : CAB International, 1992.ticks and mites. It is better to trap and then destroy rats so that 3. Varma MGR. Ticks and Mites. In : Cook G, editors : Manson’s Tropical Diseases. 20th ed London : English Language Book Society and WBtheir parasites do not escape. Saunders, 1996; 1650 -9.Mite survey for nymphs and adults is done by soil sampling 4. Sehgal S, Bhatia R. Manual on Zoonoses. National Institute of Communicable Diseases (Govt of India, Min of Health and Family welfare). New Delhimethod, whereas larvae are sampled by rodent trapping. Ticks 1981.are surveyed by flagging/ dragging method as well as by direct 5. Sonenshine DE, Lane RS, Nicholson WL. Ticks (Ixodida). In : Mullen G,host collection method through rodent trapping or by screening Durden L, editors. Medical and Veterinary Entomology. Amsterdam : Academic Press, 2002; 517-58.the host body for attached tick stages. Scrub typhus risk is 6. World Health Organisation. Arthropod borne and Rodent borne viral diseases.considered low if only up to 10% of the rats have been found Tech Rep Ser No 719. WHO, Geneva, 1985.infested on consecutive two surveys unless cases have occurred 7. Fernandez Stan, Kulkarni SM. Studies on Trombiculid Mite Fauna of India. Rec zool Surv India Occ Paper No. 212 : 1-539. Kolkata : Zool Surv India.already. 2003. • 959 •
  • 60. Three species of urban rodents, Mus musculus (house mouse), 164 Rodents Rattus norvegicus (Norway or brown rat) and Rattus rattus (roof or black rat) are the principal rodents encountered in peridomestic and domestic environments. Rina Tilak Table - 2 : Diseases transmitted through ectoparasitesRodents are the largest order of mammals with over 2000 being harboured by the rodents.living species placed in about 30 families. The word ‘Rodent’has been derived from “rodere”, which means to gnaw; the Disease Agent Vectorincisors of the rodents keep growing and to keep them in check, Murine typhus Rickettsia Fleathe rodents gnaw continuously. Rodents range in size from 5 Plague Bacteria Fleagm (pygmy mice) to over 70 kg (capybaras). They have a worldwide distribution with the exception of Antarctica. The habitat Scrub typhus Rickettsia Trombiculid miteof the rodents is equally diverse with some preferring terrestrial Indian tick typhus Rickettsia Hard Ticklife, while some live underground, others are adapted to desert Rickettsial Pox Rickettsia Mouse mitelife while some have inhabited the aquatic environment. Kyasanur Forest Disease Virus Hard TickPublic Health Importance Rocky Mountain Rickettsia Hard TickRodents are capable of transmitting a large number of diseases Spotted Feverto man through transfer of ectoparasites, which are vectorsof diseases like murine typhus, plague, scrub typhus etc. Colorado tick fever Virus Hard Tick(Table - 1 & 2) besides consuming and contaminating stored Lyme disease Spirochaete Hard Tickfood with their urine and droppings, destruction to immovableproperty, gnawing on wiring and electrical insulations etc., Human Granulocytic Bacteria Hard Tickwhich at times may lead to fire hazard. AnaplasmosisBionomics Babesiosis Parasite Hard TickRodents use their sense of vision, hearing, touch, smell and Relapsing fever Bacteria Soft Ticktaste for exploring new areas or food with certain senses more Western Equine Virus Mosquitodeveloped amongst rodents based on their needs for e.g. diurnal Encephalitisrodents have better vision as compared to their counterparts Cutaneous Leishmaniasis Parasite Sandflywho are active at night. The rodents also possess the abilityto perceive ultrasounds and use chemical, tactile, visual, Rattus norvegicus - (Sewer rat) : It generally frequents theauditory cues and intraspecific chemicals viz. pheromones for sewers. It is a burrowing rat and is easily identified by its heavycommunication. Rats tend to be cautious and mice are more body, coarse brownish to reddish grey fur with greyish belly. Itcurious. Most rodents are omnivorous with few exceptions. is a good climber, nocturnal in habit and eats anything which isThey reproduce rapidly and exhibit crepuscular to nocturnal edible. It has poor vision but keen senses of smell, touch, tastehabit. and hearing and usually lives within 150 feet of food and waterTypes of Rodents source. It feeds on familiar food, preferring meats and grainsRodents may be classified broadly into two types : viz. and has been found to be cautious of new items or food.commensal (domestic rodents) and sylvatic or wild rodents. Table - 1 : Diseases transmitted directly by rodents or through contaminated water, food or animal. Disease Agent Mode of spread Bite or scratch from an infected rodent or contact with a dead rodent, Rat bite fever Bacteria (Spirillum minus) eating or drinking food or water that is contaminated by rat faeces Spirochaete (Leptospira Leptospirosis Water & food contaminated with urine from infected animals icterohaemorrhagica) Salmonellosis Bacteria (Salmonella spp) Water & food contaminated with faeces from infected animals Bacteria (Francisella Handling infected animal carcasses, eating or drinking Tularaemia tularensis) contaminated food or water, breathing in the bacteria Haemorrhagic fever Breathing in dust that is contaminated with rodent urine or Virus with renal syndrome droppings, direct contact with rodents or their urine and droppings Lymphocytic Chorio Breathing in dust that is contaminated with rodent urine or Virus Meningitis (LCM) droppings, direct contact with rodents or their urine and droppings Plague Bacteria (Yersinia pestis) Direct contact with infected animal • 960 •
  • 61. Rattus rattus : It is a slender rat and is a very agile climber there is no rodent infestation. In low to medium infested areas,thus earning its common name - the roof rat. It usually nests no daytime rodent sightings or activity is noticed however,indoors in roof and wall cavities. It exhibits a strong fear of their presence is detected by the above mentioned methods ofnew things (neophobic). It is nocturnal and an omnivorous detection. The high-density infestation levels are detected byfeeder with preference for fruits and propensity to hoard food. daytime sightings, active gnawing, droppings and heightenedMus musculus : It resembles the roof rat, though smaller in night time sightings.size. It can be distinguished by its dusky grey fur and smallerfeet. It commonly inhabits man made structures and therefore Fig. - 2 : Rodent droppings of the three commensalcalled house mouse. It has poor vision and is colour-blind, but rodentshas a well developed sense of smell which is used to locate fooditems and recognize other mice and an acute sense of hearing torespond to unusual noises as a means of detecting and escapingdanger. Mice are omnivorous and known nibblers, eatingsmall amounts of food at a time with preference for cerealsor foods rich in fat and protein. They are poor swimmers and Norway Rat Droppings Roof Rat Droppings House Mouse Droppingstheir normal activity range is usually within 10-30 feet from Avg. Length - 3/4” Or 19 mm Avg. Length - 1/2” Or 13 mm Avg. Length-1/4” or 6mmnest. Mice are habitual gnawers, curious and avid collectors Shape - Blunt Shape - Pointed Shape - Pointedof nesting materials; a habit which can be exploited whiletrapping them by attaching nesting material to traps. Prevention and ControlThe morphological differences amongst the three commensal The best method of prevention is to deny rodents a place toor urban rodents are depicted in Fig. - 1. live / nest and food to eat. This is achieved by the following methods : Fig. - 1 : Morphological differences amongst the three Eliminating the Hiding and Nesting Sites : The rodents prefer urban rodent species. to breed in dark and undisturbed areas, which are available in ROOF RAT YOUNG RAT plenty by the debris / garbage/ clutter present in the houses/ Rattus rattus surroundings. The following measures will ensure denial of breeding / hiding place for the rodents. longer than head light, slender large pointed large large ●● Keep surroundings clean and free from debris to prevent + body large FEET HEAD rodents entry and breeding in the premises. TAIL BODY EAR EYE MUZZLE ●● Good housekeeping will deny hiding and nesting places to small small rodents. heavy, thick small small blunt ●● Deny dark, sheltered and undisturbed places in the house shorter than head + body HOUSE MOUSE by routinely displacing furniture. Mus musculus ●● Make all openings to constructions rodent proof through engineering methods. The following measures can be NORWAY RAT Rattus norvegicus adopted by individuals to make their houses rodent proof: -- Install doors to fit tightly.Detection of Rodent Infestation -- Rodent proof a door by placing sheet metal channel atIt is important to ascertain presence and level of rodent bottom and cuffs at sides, over channel.infestation prior to undertaking control measures. Following -- Reinforce doors with thick aluminium sheets of 22methods of detection may be employed for assessment : gauze or thicker.Rub marks : During movement of rodents along rat runs, the -- Steel wool and copper mesh can be packed tightly intooil and dust from the body of the rodents leaves rub marks holes to close openings or protect other areas fromespecially in case of roof rats. gnawing.Gnawing marks : Due to the continuous gnawing habit of -- Make the drainage points rodent proof by using sievesrodents, wood scrapings around doors, windows and frames secured with cement.may be the obvious visible signs of rodent activity. -- Use materials such as mortar for sealing holes inDroppings : By seeing the droppings, it is possible to identify concrete buildings.the type of rodent infesting a given structure. The same has -- Fill all gaps in basements/ building or holes in wallsbeen presented in Fig. - 2. Droppings are ideally visible along with cement or steel wool.rat runs, near rodent burrows and at the feeding sites. -- Rodent proof utility wires to limit access to buildingsRun Ways : Rodents generally use the same path for travelling; using rolling plastic tubes made from rectangularthe common runways or rat runs are seen along walls, behind sheets of plastic. The tube rolls when the rodent triesstored objects and similar places. to walk over it.On inspection, when no signs are visible, it is presumed that -- Rodent proof air vents and chimneys using 1/4” hardware cloth. • 961 •
  • 62. Eliminating Food Sources may be present. Traps should be laid out at or before dusk●● Spillage should be cleaned daily. along rat runs, near their feeding areas, areas of high activity●● Garbage should not be stored outside in plastic bags as or potential entry points. Traps should be placed at 3-10 ft plastic garbage bags are not rodent-proof, instead metal apart for mice and about 20 ft for rats. It is also pertinent to bins or heavy duty plastic bins with tight-fitting lids use the correct trap for the rodents; larger rodents may require should be used. larger traps as compared to traps used for mice. For successful●● Fallen fruits and nuts from the ground should be promptly trapping, it is advisable that baited traps should be placed. disposed of. Types of Traps : There are various types of traps available in●● Pet food dishes and leftovers should also be promptly the market for use. The traps either trap live rats or kill the removed after feeding. rats. Commonly available traps are :●● Animal waste should be cleaned frequently. Cage Traps (Fig. - 3)●● Food scraps should not be placed in compost piles. ●● Used for capturing rodents live.●● Food grains or other food materials should be stored in ●● These traps are designed to catch and hold one or more rodent proof containers and wherever feasible be placed animals by means of a falling or sliding door, triggered in cupboards. when the rodent enters or nibbles at a bait.In situations where preventive measures have failed to address Sherman Traps (Fig. - 4)the problem of rodent nuisance effectively, control of rodentinfestation is achieved through the following three methods : ●● Are foldable box traps made of Aluminium. ●● Used for trapping rodents for research purposes or during●● Trapping epidemic investigation (Procedure of trapping is presented●● Baiting in Box - 1).●● Fumigation ●● Traps live rodents.Trapping : Trapping can be an effective method of controlling ●● Have an added advantage of ensuring that ectoparasitesrodents, but it requires more skill and labor than most other are not lost, even if the trapped rodent dies.methods. Trapping is recommended where poisons seem ●● Generally baited with freshly made baits rich in fat e.g.inadvisable and is the preferred method to try first in homes, pakoras (fried snack of onion mixed with gram flour) orgarages and other small structures, where only a few rodents fried fish, chicken etc. Box - 1 : Trapping Procedure for Rodents using Sherman Traps Number the Sherman traps with marking pens starting from 1-40. Prepare flags bearing the same numbers i.e. 1-40 with cardboard pieces. Carry freshly prepared pakoras for the traps. The laying of traps should be carried out in the late afternoons and should be completed before dusk. Personnel involved in laying/ collecting of rodent traps should wear trousers tucked in boots/anklets and full sleeved shirt. Wear heavy duty gloves while laying/ collecting traps and use repellents on exposed skin. Identify suspected mite islands (a patch of ground with vegetation, temp in the range of 27± 5°C, Relative Humidity in the range of 80-100% and which provides an ideal place for rodents to hide). Check the working condition of Sherman trap before placement. Place pakora in traps; ensure it is placed at the closed end of the trap. Place the trap in the bushes or where rodent is likely to frequent. Place the trap with its opening facing the likely direction of rodent entry. Ensure that the trap opening is not obstructed. The trap should be placed on flat ground so that it does not tumble if approached by rodent or any other movement in the area. Place flag bearing the same number as the trap, close to the trap so that it is visible from a distance. Tie a bandage to the nearby bush to indicate the site of trap placement to enable retrieval in the poor light conditions of dawn - the time for trap collection. Make a spot map of trapping area with the trap numbers indicated on the map. Collect the trap before dawn next day. Use heavy duty gloves and a torch for collection of traps at dawn. (All protective measures as followed earlier should be ensured). If a trap is closed, do not try to open the trap, put the trap in a cardboard carton for transportation to the lab. If a trap is open, fold it and place in carton/ plastic bags. Once the traps are brought to the laboratory, the rats are transferred in to large polythene bags, anaesthetized, blood collected for testing for presence of rodent borne diseases by conventional serology/ PCR, rodent identified and thereafter subjected to ectoparasite screening. • 962 •
  • 63. Fig. - 3 : Cage Trap Fig. - 4 : Sherman TrapTrigger or Snap Traps that of fly papers. It entangles mice and rats in much the same●● These traps are generally more effective than cage traps. manner as flypaper catches houseflies. Like traps, glue boards●● Simple, inexpensive, wood-based snap traps are readily need to be placed along walls where mice and rats travel. It is available. however important to place the glue boards in dust free areas●● For rats, bait the traps with fried food items like chicken, and away from direct sunlight or extremes of temperature so pakoras etc. tied securely to the trigger. that the tackiness of the glue is maintained.Break Back Traps Baiting : In the event of emergency rodent control or at times●● These traps are similar to snap traps but have a quicker when there is a failure to achieve effective rodent control killing action and hence there are no misses. through non chemical strategies mentioned in the preceding●● These traps are considered more humane as the rats die paragraphs, baiting emerges as an attractive alternative to instantaneously. address the problem. The process of baiting utilises special●● They are generally used in fields by farmers. chemicals called rodenticides for killing the rodents. The use●● Not preferred indoors. of rodenticides or the process of baiting should be undertaken●● Traps need to be baited with food similar to that used for by trained individuals and requires utmost care as they pose other traps. threat to non target organisms, as well as hazards of accidental/ deliberate poisoning.Advantages : Trapping is an effective rodent control optionwhen permanent rodent control measures are not in place or Factors Influencing Baiting : The adaptive behaviouralinappropriately implemented. It is one of the most preferred responses of rodents for selecting palatable and nutritiousand safer rodent control options in domestic and peri- food, while rejecting palatable though harmful food poses onedomestic environments. It has an advantage that it allows of the biggest challenges in making the rodents consume theuser satisfaction in terms of success of the trapping procedure toxic baits. This is further challenged by the phenomenon ofbeing obvious. Trapping as a rodent control option also ensures ‘neophobia’ exhibited by rats and their learned food aversions.proper disposal of carcasses or live trapped rodents thereby It is thus essential to undertake ‘prebaiting’ (the food materialpreventing odour nuisance from the dead rodents. Traps are without the bait is placed for 3-5 days to remove fear of newespecially effective indoors where use of rodenticides may pose food amongst the rodents) prior to actual baiting. It is furtherthreat to the non target organisms viz. people or pets and in important that the rodenticide should preferably be tastelesskitchens, pantries or food serving areas due to possibility of and odourless in lethal concentrations and have a delayedcontamination of food. effect.Limitations : This is a temporary control option as after initial Time & Place of Baiting : Baiting should be done in thesuccess, the rodents become ‘trap wise’ (a phenomenon wherein evenings along rat runs, feeding and activity areas etc which arerodents avoid traps as they are able to associate traps and their generally frequented by the rodents as evidenced by the signsgetting trapped in them) and the efficacy of the trapping process of infestation elicited through the procedure given earlier.is then compromised. The trapping process should be stopped Types of Rodenticides : Rodenticides are classified as acutewhen rodents are sighted but are not being trapped. rodenticides and anticoagulants. They are used mostly mixedGlue Boards : Glue boards are an alternative to rodent traps with food or as contact poisons in the form of dusts (trackingand may control rodents in low infestation areas. They are powder).effective options for rodent control in areas where food is Acute Rodenticides : These kill the rodents on ingestion ofcommercially prepared, where the use of rodenticides is unsafe a single dose of the toxic bait. There are a large number ofand for monitoring rodent population. A combination of traps acute rodenticides, however, not all are considered ideal for useand glue boards may prove more advantageous than a single in domestic environments due to safety concerns. The acutemethod. The mode of action of rat glue boards is the same as rodenticides are Red squill, Norbromide, Sodium fluoroacetate, • 963 •
  • 64. Strychnine, ANTU etc. Some commonly available acute can be mixed with wheat flour and made into baits as inrodenticides are Zinc phosphide and Barium carbonate. case of Warfarin.Zinc Phosphide : It is a black powder with a garlic odour. Advantages : The greatest advantage of these products are thatThe garlic odor attracts rodents but has a repulsive effect on they cause apparently painless deaths and hence do not resultother mammals, though, birds cannot perceive the smell and in the development of ‘bait shyness’ and therefore can be usedunintentionally feed on them leading to unwarranted death. wherever continuous rodenticiding is required e.g. granaries,It is mixed in the proportion of 1 : 8 or 1 : 10 with wheat flour ships etc.and made into pellets with a little edible oil. Upon ingestion, Limitations of Multiple Dose Rodenticides : As multiple doseZinc phosphide reacts with dilute acids in the gastrointestinal consumption of the bait is required for the desired kill; singletract and produces phosphine which enters the blood stream dose consumption of the bait will lead to sublethal dosingand causes death within four hours of consumption of a single thereby giving rise to development of resistance.dose of the bait. (b) Single Dose Anticoagulants : Are derivatives ofBarium Carbonate : It is a white powder mixed in the 4-hydroxycoumarin and are referred to as second generationproportion of 1 : 4 with wheat flour. A single dose consumption anticoagulants or as “superwarfarins”. These are far moreof the product causes kill within eight to twenty four hours. toxic and lethal than their first generation counterparts andAdvantages : Being highly toxic, these rodenticides bring are applied in lower concentrations in baits (0.001 - 0.005%).about a rapid kill with a single dose consumption of the bait, The rodents die after ingestion of a single dose of the bait aswhich is one of the greatest advantages especially when the in case of the acute rodenticides, however, the cause remainsrodent populations are very high. haemorrhage. Single dose anticoagulants commonly used areLimitations : These rodenticides need to be used with care Bromadialone, Difethialone, Brodifacoum etc. Bromadialoneas they may cause toxicity to non target organisms. The is used in the form of ready-to-use baits of low concentrationconsumption of a single dose of the bait leads to very painful containing 0.005% bromadialone. Single dose consumption ofdeath of the rodent, which when sighted by the other rodents the bait kills the rodents. Bromadialone kills all the commensalis quickly registered as an association of the new bait with rodents viz. sewer rats, roof rats, house mice and is alsothese deaths, thus leading to avoidance of the bait - i.e. effective against Warfarin resistant sewer rats.development of the phenomenon termed as “bait shyness”. Advantages : These single dose anticoagulants are effectiveOnce this develops, baiting with acute rodenticides is rendered against strains of rodents that have developed resistance toineffective and needs to be discontinued. first generation anticoagulants. A single dose is lethal to causeAnticoagulants : These substances kill by preventing normal kill and hence development of resistance also may not takeblood clotting and causing internal haemorrhage through place readily.effective blocking of vitamin K cycle, which results in inability Limitation : As a single dose of these rodenticides is lethal toto produce essential blood-clotting factors (mainly coagulation rodents; the use of this class of products may pose threat tofactors II (prothrombin), VII (proconvertin), IX (Christmas non target organisms and hence needs to be used with care andfactor) and X (Stuart factor)). The antidote to anticoagulant under supervision.poisoning is therefore Vitamin K itself. Anticoagulants are of Fumigation : Fumigation is the choice method for killingtwo types, multiple dose and single dose anticoagulants. rodents in burrows, enclosed structures / places. It is however,(a) Multiple Dose Anticoagulants : These are the earliest known carried out by trained professionals due to the risk posed byanticoagulants also called the first generation anticoagulants. the noxious gases released during the process. The fumigantsMultiple dose consumption of the product kills the rodents, commonly used are Aluminium phosphide and Calcium cyanide.which generally takes about 1-2 weeks post ingestion of lethal Sulphur dioxide, Carbon disulphide, Carbon monoxide anddose. The common examples in this category are : Methyl bromide are also used especially in godowns, granaries●● Warfarin : It is the earliest product used for rodent control and aircrafts. from this category. The product is not a very popular Fumigation with Aluminium phosphide and Calcium cyanide product now for rodent control as it has a delayed action. involves identification of burrows, locating the exit and entry This product requires a higher concentration of the toxicant points and then sealing one of the ends. The fumigants in the (usually between 0.005 and 0.1%) and consecutive intake form of tablet (Aluminium phosphide) or in the form of powder over days in order to accumulate the lethal dose. The (Calcium cyanide - 30 g /rodent burrow) are introduced in the product is mixed in the proportion of 1 : 19 with wheat burrows and the burrow closed with wet soil to release the gas flour and made into baits. - (Phosphine in case of Aluminium phosphide and Cyano gas●● Coumatetralyl : Is an anticoagulant of the Warfarin in case of Calcium cyanide). Fumigation with Cyano gas has type. The toxicity of the product is known to increase been extensively used in India for fumigating rat burrows in with continued ingestion or exposure to the bait. For the fields during Plague outbreaks, whereas Aluminium phosphide product to be toxic, it should constantly remain present tablets are generally preferred for use in peri-domestic areas in the blood for more than 1 to 2 days. A single exposure, and agricultural fields. even though relatively large, may not produce toxic Ultrasonic Repellent Device : The ability of rats to perceive symptoms as the compound is quite rapidly metabolized. ultrasonic sound has been exploited by using devices generating It is marketed in India as tracking powder (0.0375%) which ultrasonic sounds. These are electrical devices and are popular • 964 •
  • 65. gadgets claiming efficacy in repelling rodents from infested Other alternative are use of glue boards, baiting & use ofrooms. Ultrasonic sounds, however, have very limited use in rodenticides. The acute rodenticides are Red squill, ANTU, Zincrodent control as they are directional, don’t penetrate behind phosphide & Barium carbonate (advantage of rapid kill but canobjects and lose their intensity with distance. They can be used lead to development of bait shyness.), the other rodenticidesin small rooms in a limited area. are the anticoagulants. Multiple dose anticoagulants are Warfarin & Coumatetrayl; They have the advantage of causingSummary painless deaths but multiple dose consumption is required forRodents are the largest order of mammals with over 2000 the desired effect. Single dose anticoagulants (bromadiolone)living species. ‘Rodent’ has been derived from “rodere”, which have the advantage of killing the rodents by consumption ofmeans to gnaw. Rodents range in size from 5 gm to over 70 kg. a single dose with the added advantage of anticoagulantsRodents are capable of transmitting a large number of diseases i.e. no development of bait shyness takes place, thus makingto man through transfer of ectoparasites, which are vectors of them ideal for continuous use. Fumigation can be done usingdiseases like murine typhus, plague, scrub typhus. Rodents Aluminium phosphide and Calcium cyanide.use their sense of vision, hearing, touch, smell and taste forexploring new areas or food. The rodents also possess the Study Exercisesability to perceive ultrasounds and use chemical, tactile, visual, MCQs & Exercisesauditory cues and intraspecific chemicals like pheromones for 1) Which of these is known as roof rat (a) Mus musculuscommunication. (b) Rattus norvegicus (c) Rattus rattus (d) All of these.Rodents are broadly classified into domestic & wild rodents; 2) Rodents are capable of transmitting which of theseprincipal rodents encountered in peridomestic and domestic diseases to man through vectors (a) Murine typhusenvironments are Mus musculus (house mouse), Rattus (b) Leptospirosis (c) Rat bite fever (d) All of these.norvegicus (Norway or brown rat) and Rattus rattus (roof 3) Detection of rodent infestation prior to deciding controlor black rat). Rattus norvegicus or the sewer rat generally measures can be done by (a) Rub marks (b) Gnawing marksfrequents the sewers. It is a burrowing rat and is easily (c) Droppings (d) All of these.identified by its heavy body. Rattus rattus is a slender rat & 4) This trap is generally used for trapping rodents foris a very agile climber. Mus musculus has dusky grey fur and research purposes / outbreak investigation (a) Cage trapssmaller feet. Detection of rodent infestation can be done by rub (b) Sherman traps (c) Trigger trap (d) Break back traps.marks, gnawing marks, droppings & runways. Rodents are 5) Acute rodenticides are all except (a) Red squill (b) ANTU (c)mostly omnivorous with preference for cereals or foods rich in Zinc phosphide (d) Warfarin.fat and protein. Fill in the BlanksPrevention is achieved by denying rodents a place to live/ nest 6) Burrowing rat which is easily identified by its heavy body,and food to eat, keeping surroundings clean and making all coarse brownish to reddish grey fur with greyish belly &openings to constructions rodent proof etc. Food source need to frequents sewers is _______________be eliminated and garbage should not be stored outside, animal 7) These traps have a quick killing action & are generallywaste should be cleaned and food grains / other food materials used in fields_______________should be stored in rodent proof containers. True or FalseControl of rodent infestation is achieved through trapping; The 8) Rodents range in size from 5 gm (pygmy mice) to overtraps used are Cage traps, Sherman traps, Snap traps & Break 70 Kg.back traps. Traps should be laid out at or before dusk along rat 9) Mice are omnivorous and known nibblers, eating smallruns, near their feeding areas, areas of high activity or potential amounts of food at a time with preference for cereals orentry points. Traps are the most preferred and safe rodent foods rich in fat and protein.control options in domestic and peri-domestic environments as 10) Traps should be placed at 3-10 ft apart for mice and aboutsuccess of the trapping procedure being obvious, they however 20 ft for rats.have the limitation of being temporary control options as the Answers : (1) c; (2) a; (3) d; (4) b; (5) d; (6) Rattus norvegicus;rats become trap wise. (7) Break back traps; (8) True; (9) True; (10)True. • 965 •
  • 66. to family Hydrophilidae. The members of family Viperidae are 166 Snakes divided into two subgroups viz. the pit vipers and the typical vipers; they possess long fangs which are normally folded up against the upper jaw and are erected while striking. Rina Tilak Fig. - 1 : Venom apparatus of a snakeSnakes are one of the most widely distributed animals spanningacross continents (with the exception of Antarctica), inhabiting Venom glandthe sea and present as high as 16,000 feet (4900m) in theHimalayan Mountains, though conspicuous by their absencefrom Ireland and Iceland (1). There are over 3000 species ofsnakes distributed world wide and about 275 species are foundin the Indian sub-continent (2).Morphology & BiologySnakes, which belong to the class Reptilia, are limbless reptilescharacterized by elongated body which is divided into head,body and tail. The whole body of the snake is covered with Venom ductscales which are an important tool for their identification. A Venom canalthin skin, in turn covers the scales which is periodically shedor cast off during the process of moulting; during this periodthe snake is blind (as the skin covers the eyes as well) andlethargic. Venomous Indian Snakes : The important venomous snakesSnakes locate their prey by their senses of vision, smell or in India are Cobra (Naja naja), Common Krait (Bungarusthermo-sensitivity. The remarkable vision of some snakes caeruleus) and three types of vipers i.e. Russell’s (Daboiaenables them to detect movement; snakes smell by using their russelii), Saw scaled (Echis carinatus) and the Hump nosedforked tongue which collects airborne particles and then passes viper (Hypnale hypnale). The polyvalent antivenom availablethem to the Jacobson’s organ or the vomeronasal organ in the as of now in India, however, has the antivenom targetedmouth for examination. The body of the snakes which is in against poisoning by only the first four types of snakes. Thedirect contact with the ground is also very sensitive to vibration, identification of snakes is a very specialized task and is best leftthus enabling snakes to sense other approaching animals by to the herpetologists, however, certain common identificationdetecting vibrations on the ground. Some snakes like pit vipers marks and distribution of the venomous snakes of India isand pythons have infrared-sensitive receptors present between presented below:the nostril and eye or have labial pits on their upper lip just a) Cobra: Found all over India, are active during day andbelow the nostrils (common in pythons) which allow them to night. Raises a hood which may have no mark e.g. king cobra“see” the radiated heat and thus locate prey especially warm- (Ophiophagus hannah), or hood may be spectacled or bicellateblooded mammals. (Naja naja) or monocled (monocellate i.e. single circular mark)Of the roughly 725 species of venomous snakes worldwide, - Naja kaouthia (Fig. - 2).only 250 are able to kill a human with one bite. The official b) Krait: Found all over India, are generally encountered atrecords state about 2, 50,000 snakes bite cases occur in India night. It is the most venomous of all land snakes. The commonevery year, of which, over 50,000 die due to inadequate first aid krait or Bungarus caeruleus is identified by paired white linesor unscientific treatment methods (3). The Indian snake bite on the body, whereas the other variety is the banded kraitstatistics are alarming as the figures are highest in the world, Bungarus fasciatus (Fig. - 3).though India does not host the largest number of snakes in theworld. c) Saw Scaled Viper: Found all over India and prefers dry scrub or desert. Echis carinatus is identified by the White loop marksVenom Apparatus along body and arrow or birds foot mark on head (Fig. - 4)The Venom apparatus of a snake (Fig. - 1) comprises a venom d) Russell’s Viper: Found throughout India up to 3000 mgland which opens through the venom duct into fangs located altitude. Daboia russeli is identified by the black edged chainin front of the upper jaw which have a venom canal along which like marks and white V on head (Fig. - 5)venom is introduced while biting into the tissues of the prey. Ifa human is bitten, venom is injected either subcutaneously or e) Hump Nosed Viper: Hypnale hypnale, the hump nosedintramuscularly. viper is found in the Western ghats. It is identified by its characteristic hump nose, whereas the other features resembleClassification of snakes Echis carinatus (Fig. - 6).The venomous snakes of the Indian continent may be broadly Snake Venomclassified into two important families i.e. Elapidae andViperidae. Snakes belonging to family Elapidae are the Cobras, Snake venom contains more than 20 different constituentsKraits and Coral snakes. This group is characterized by the which evoke varied responses in the body. These constituentspresence of short permanently erect fangs. Sea snakes belong are: procoagulant enzymes, haemorrhagins, cytolytic or • 966 •
  • 67. Fig. - 2 : Hoods of Cobra Fig. - 4 : Saw scaled Viper Photo courtesy Ian Simpson Fig. - 5 : Russell’s viper Fig. - 3 : Morphology of Kraits Common Krait Banded Krait (Bungarus caeruleus) (Bungarus fasciatus) Photo courtesy Ian Simpson Fig. - 6 : Hump nosed Vipernecrotic toxins, haemolytic and myolytic phospholipases A2,pre-synaptic neurotoxins and post-synaptic neurotoxins. It isimportant to note that not all venomous snake bites lead toclinical effects as most of the time insufficient or no venomenters the wound.Envenomation Symptoms : The local symptoms and signs ofsnake bite are fang marks, local pain and bleeding, bruising,lymphangitis, lymph node enlargement, inflammation (swelling,redness and heat), blistering, local infection, abscess formationand necrosis. The systemic action of snake venom is either onthe nervous system (Neurotoxic) or on the haematologicalsystem (anti-haemostatic). It may also cause local damageor reaction as a result of the constituents of venom whichprimarily function to spread the venom throughout the body.Symptoms seen in neurotoxic type (due to elapid bites) aredrooping eyelids, vision disturbances, difficulty in breathing, • 967 •
  • 68. difficulty in speaking, opening of mouth or protruding the Prevention of Snake Bitestongue, difficulty supporting the neck and head and difficulty Snake bites can be effectively prevented by following certainin swallowing. The presentation in haematoxic type (due to simple preventive measures; the following do’s and don’tsvipers) is continuous bleeding from bite site, bleeding from should be followed to prevent snake bites:gums or nose, appearance of bruises and dark urine. ●● Do not try to kill a snake. Many people are bitten becauseSyndromic Approach as Guidelines they try to kill a snake or get too close to it- leave snakesA “syndromic approach” as laid down by WHO may be useful alone.in prompt and effective management of snake bite especially ●● While trekking/ hiking, stay out of tall grass unless you arewhen the snake has not been identified; the envenomation wearing thick leather boots and remain on hiking paths assymptoms provide the relevant guidelines as presented in much as possible.Table - 1. ●● Keep hands and feet out of areas you cannot see. Do not pick up rocks or firewood unless you are out of a snake’s Table - 1 : Snake identification based on Envenomation striking distance. Syndrome ●● Be cautious and alert when climbing rocks. ●● Wear boots and avoid moving barefoot in snake infested Envenomation Syndrome Snake species areas. Local swelling with bleeding/ All Viper species ●● Always carry a torch while moving in darkness. clotting disturbance ●● Remove garbage or any other junk material lying in and ●● Above + Shock or renal failure ●● Russell’s & Saw around the house - keep surroundings rubble free. scaled viper ●● In snake infested areas, shake shoes well before wearing. ●● Ptosis, external ophthalmo- ●● Russell’s viper ●● Dust bedding before sleeping, use mosquito nets while plegia, facial paralysis and - reported from sleeping in camp sited areas and preferably avoid sleeping dark brown urine South India on ground. ●● Paralysis with dark brown urine ●● Russell’s viper First Aid and renal failure along with - reported from Whenever dealing with a snake bite case, it is pertinent to bleeding/clotting disturbance South India remember that a substantial proportion of all snake bites are Paralysis with minimal or no Krait actually due to non-poisonous snakes; secondly, almost 50% of local envenoming bites by venomous snakes do not inject enough poison and hence it is important to reassure the person. The following measures Local envenoming (swelling etc) Cobra or King cobra (Do’s & Don’ts) can save lives even in case of venomous snake with paralysis bites, if timely action is taken (See Box - 1). Box - 1 : Snake Bites - Do’s and Dont’s Do’s Calm the patient down to slow down blood circulation and retard the spread of venom. Have the victim lie down with the affected limb lower than the heart. Immobilize the bitten limb, using a splint if possible and position it below the level of the heart. Get the victims to hospital urgently, lying flat, if possible - do not wait for the symptoms to develop. Start Artificial Respiration, this can be life saving in Cobra and Krait bites as the victim may stop breathing, however they are not dead. Remove any rings, bracelets, boots, or other restricting items from the bitten extremity as it may swell. Start antivenin in hospital after assessment of envenomation symptoms by a qualified medical person. Don’ts Do not apply any tourniquet or compression bandage (4). Do not give incision or attempt to suck out venom as it is ineffective at removing venom; and in Viper bites will cause serious bleeding. Do not give the victim alcoholic drinks or Aspirin. Do not wash the bitten area as it may increase the venom flow. Do not cool the area of the bite. Do not try to catch the snake; we do not need another victim. If the snake has been killed, take it to the hospital. Do not give antivenin in any other place other than in a hospital. • 968 •
  • 69. Acknowledgement: The author gratefully acknowledges the Antivenom should only be given in a hospital after assessmentinputs by Ashok Captain, a well known Indian Herpetologist of envenomation. It is not advisable to apply any tourniquet orand Ian Simpson for the photographs. compression bandage or give incision. The victim should not be given any alcoholic drinks or Aspirin nor should the bittenSummary area be washed.Snakes are one of the most widely distributed animals. Thereare over 3000 species of snakes distributed worldwide and Study Exercisesabout 275 species are found in the Indian sub-continent. Snakes MCQs & Exercisesbelong to the class Reptilia, are limbless and characterized by 1) The common poisonous snakes of India are (a) Cobraelongated body which is divided into head, body and tail. The (b) Common Krait (c) Russell’s vipers (d) All of these.whole body is covered with scales, which are covered by skin. 2) Which of these should not be done in case of snake biteThe skin is shed or cast off during the process of moulting. (a) Victim should be made to lie down with affected limbSnakes locate their prey by their senses of vision, smell or lower than the heart. (b) Give incision (c) Start artificialthermo-sensitivity, body is also very sensitive to vibration. Of respiration (d) Start antivenomthe roughly 725 species of venomous snakes worldwide, only Fill in the Blanks:250 are able to kill a human with one bite. 3) Snakes belong to the class __________The snakes are classified into families: Elapidae and Viperidae. 4) The most venomous of all land snakes, identified by pairedElapids are the Cobras, Kraits and Coral snakes. Viperidae white lines on the body is__________are further divided into two subgroups- the pit vipers and the 5) The skin which covers the scales of snakes is periodicallytypical vipers. The important venomous snakes in India are shed of & the process is called as __________Cobra, Common Krait and the three types of vipers i.e. Russell’s, True or false:Saw scaled and the Hump nosed viper. 6) The body of the snakes which is in direct contact with theNot all venomous snake bites lead to clinical effects as most of ground is not very sensitive to vibration.the time insufficient or no venom enters the wound. The local 7) Drooping eyelids, vision disturbances, difficulty insymptoms and signs of snake bite are fang marks, local pain breathing, difficulty in speaking are symptoms seen in biteand bleeding, bruising, lymphangitis, lymph node enlargement, due to elapids.blistering, local infection, abscess formation and necrosis. The Answers: (1) d; (2) b; (3) Reptilia; (4) Krait; (5) Moulting;systemic action of snake venom is either on the nervous system (6) False; (7) True.or on the haematological system. Neurotoxic symptoms due toelapid bites are drooping eyelids, vision disturbances, difficulty References & Further Suggested Readingin breathing, difficulty in speaking and opening the mouth. 1. Conant, Roger. A Field Guide to Reptiles and Amphibians Eastern/Central North America. Boston, Massachusetts: Houghton Mifflin Company. 1991;Haematoxic symptoms (due to vipers) are continuous bleeding pp.143.from bite site, bleeding from gums or nose, appearance of 2. Whitaker Romulus, Captain Ashok. Snakes of India: The Field Guide (2004)bruises and dark urine. pp 11 -13. 3. Sinha, Kounteya (25 Jul 2006), “No more the land of snake charmers...”,Prevention of snake bite is by avoiding snake infested areas, The Times of India.staying out of tall grass, while hiking-keeping hands and 4. Simpson Ian D. Modern Snakebite First Aid for the Wilderness Environment.feet out of areas one cannot see, wearing boots, keeping W.H.O. Snakebite Treatment Group. Tamil Nadu Government Snakebite Taskforce.surroundings rubble free & dusting the beds before sleeping. 5. Simpson ID, Norris RL. Snakes of medical importance in India: is the conceptFirst aid involves reassurance, making the victim lie down with of the ‘Big 4’ still relevant and useful? Wilderness Environ Med. 2007; 18 (1): 2 - 9.the affected limb lower than the heart. It is important to startartificial respiration and remove any rings, bracelets, boots etc. • 969 •
  • 70. Anopheles Mosquitoes Identification : Group - I Costa uniformly dark i.e. not interrupted by any pale spot. Also no white spot on the wing field Anterior forked cell much larger than the posterior Anterior forked cell of nearly the same size A. aitkeni as posterior Distinct white banding at the distal end of hind Banding absent. femur; frontal white scale tuft present. Scale tuft absent A. barianensis A. culiciformis • 970 •
  • 71. Anopheles Mosquitoes Identification : Group - II Less than four dark spots, involving the costa, sub costa and vein 1 Palpi with distinct pale banding Palpi Unbanded A prominent tuft of scales black above & Hind femur with a No such tuft of Hind femur without white below, about conspicuous white band scales present any white band femoro-tibial joint of A. lindesayi hind legs A.annandalei a) Inner quarter of costa a) Inner quarter of Palpi shaggy. Fringe spot Palpi thinner. Fringe spot with marked pale costa dark. at V 5.2 present. Presence at V 5.2 absent. Only dark interruptions. b) Tip of wing golden. of both dark and white scales on the wing field. b) Wing fringe between A dark mosquito scales on wing veins. A rare species in India. V 5.2 and 6 white. A A common species b r i g h t l y coloured mosquito A. gigas A. hyrcanus var A. barbirostris A. umbrosus nigerrimus Group III to VI have at least 4 dark spots involving the costa, sub costa and vein 1. • 971 •
  • 72. Anopheles Mosquitoes Identification : Group - III Dark footed series (of hind legs only). Femorae & Tibiae not speckled Tips of palpi dark Tips of palpi pale Wing veins except on costa All wing veins contain V 3 mostly dark V 3 mostly pale & V 1 contain only dark scales both dark & white A. dthali scales 2 indefinite dark spot on 3 definite dark spots Only 2 fringe spots Fringe spots at all V 6 the distal one being on V 6 V 4.2 and 5.1 present veins except V 6. very long A. multicolor (palpi of normal (palpi very long) A. turkhudi length) A. sergenti A. culicifacies The two apical pale bands are of equal or The two pale apical bands are nearly equal length and the intervening dark definitely unequal area is small No fringe spots Fringe spots at V 6 The intervening dark The intervening dark area at V 6 A. aconitus area on the palp is is either of the same size much larger than as the apical pale band, either of them or very much smaller. Broad white bands at the Basal area of the costa Basal area of the costa tarsal joints of the front dark without any with one pale interruption legs. pale interruption A. minimus A. varuna The dark area is of The dark area is Inner third of costa Inner third of costa the same size as very much smaller. uninterruptedly dark interrupted the apical area. A. vagus A. subpictus 2 dark spots on 3 dark spots on Tarsal joints of leg 1 Tarsal banding of V 6. Tibiotarsal V 6. Tibiotarsal banded. Fringe leg 1 absent. joints dark. and tarsal joints spot at V 6. No fringe of front legs spot at V 6 A. fluviatilis narrowly banded. A. jeyporiensis A. superpictus A. moghulensis • 972 •
  • 73. Anopheles Mosquitoes Identification : Group - IV Dark footed series (Hind legs only). Femorae & Tibiae speckled 3 pale bands on the palp 4 pale bands on the palp The apical and the sub The apical and the sub Broad tibio-tarsal The three distal bands apical bands are apical bands are white bands on the are much broader equally broad unequal the former hind leg then the proximal being broader than band which is narrow A. stephensi the latter A. leucosphyrus A. tessellatus A. sundaicus • 973 •
  • 74. Anopheles Mosquitoes Identification : Group - V White footed series (Hind legs only) Femorae & Tibiae not speckled Only tarsus 5 and 1/3 rd of tarsus 4 At least tarsal segments 3, 4 and 5 of of hind legs completely white hind legs completely white 3 pale bands on the palp 4 pale bands on the palp A. majidi A. karwari Vein 5 mainly dark with a Conspicuous white scales on dark spot at its bifurcation Vein 5 extensively pale and the dorsum of the abdomen no dark spot at its bifurcation & thorax A. annularis A. pulcherrimus Distal end of tarsus 1 of Distal end of tarsus 1 of hind legs conspicuously hind legs dark marked white A. pallidus A. philippinensis • 974 •
  • 75. Anopheles Mosquitoes Identification : Group - VI White footed series (Hind legs only). Femorae & Tibiae speckled Half of tarsus 5 of hind Whole of tarsus 5 and Whole of tarsus 5 and 4 At least tarsi 3, 4 and 5 legs white. Prominent 1/3 of tarsus 4 of hind legs of hind legs white of hind legs completely scale tufts on the ventral white with a dark band white. surface of each on tarsus 4. A. theobaldi abdominal segment. A. maculatus A. kochi A. maculates var willmori Two equally broad pale apical bands, palpi The two pale apical speckled bands are unequal A. splendidus At least the last two Dark scales on the abdomen Conspicuous white scales on the segments of the dorsum dorsum of the thorax and abdomen of the abdomen covered (Femorae and tibiae may be speckled with golden scales A. ramsayi or not speckled) A. pulcherrimus A. jamesi • 975 •

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