Entomology

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Entomology for Medical students

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Entomology

  1. 1. 1-3mm• Members of class insecta, order diptera• 127 families, >85,000 species.• Diptera - most important 18-22mm vectors human disease. > 1 million deaths p.a. 1 1-1.5mm
  2. 2. Flies - blackfly 1-3m mFamily Simuliidae.• Simulium damnosum, S. neavei - important vectors in Africa.• Simulium ochraceum - important vector in New World (Australia – New Zealand)• Breeds close to fast moving water or water falls – Eggs are laid on running water, larvae attach on submerged structures e.g. rocks, trees & vegetation – S. neavei in Africa occur on arthropods 2
  3. 3. Black fly 1-3mmEffects on hosts. Allergic reactions. "Blackfly fever" Vector - Onchocerca volvulus – filarial nematode. Vectors - Leucocytozoon spp. - "malaria" in birds. 3
  4. 4. Midges. 1-1.5mmEffects on vertebrate hosts:• Annoyance.• Vectors of Acanthocheilonema perstans -filarial parasite humans and other filarial nematodes. 4
  5. 5. TabanidsOrder Diptera.Suborder Brachycera 18-22mmFamily Tabanidae.• ~ 4000 species• Females intermittent parasites• Males not parasitic• Adults - large body (6-25mm long)• Large eyes - facilitates host location• Mouthparts - cut large wound, where they feed from a formed pool of blood 5
  6. 6. (c). Flies - tabanids & bacteria. 18- 22m mSuborder Brachycera, Family Tabanidae.• Mechanical vectors: – Bacillus anthracis – anthrax. – Francisella tularensis - tularemia – deerflies Chrysops spp.• Blood lossImportant genera:• Tabanus 6
  7. 7. Flies - tabanids 18-22mm• Vectors Loa loa, - filarial nematode.• “Eye worm“.• Vectors for Chrysops spp. (deerflies).• C. dimidiata - most important. 7
  8. 8. Flies - tsetse flyFamily Glossinidae, genus Glossina.• Hosts & vectors of trypanosome protozoans.• Trypanosoma brucei species complex.• Sub-saharan Africa. 8
  9. 9. Flies - sandfliesFamily Psychodidae Phlebotomus & Lutzomyia species• Vectors of Leishmania - protozoa• Cutaneous leishmaniasis (L. tropica - Old World• L. mexicana- New World)• Mucocutaneous leishmaniasis (espundia) - L. braziliensis• Visceral leishmanisis (kala azar) - L. donovani 9
  10. 10. Sand fly• Sand flies • Phlebotomus & Lutzomyia • Short mouth parts, pool feeders • Only ♀♀ take blood • Vector of Leishmania, bartonellosis (bacterial) & sand fly fever (viral)• Less than 5mm length, hairy body & wings• Old world species live in arid/semi- arid conditions, new world species are forest dwellers • Epidemiological implication• Have limited flight range close to breeding sites• Most active at twilight, night & shade 10
  11. 11. House fly• Musca domestica• Domestic flies act as mechanical vectors of many diseases 11
  12. 12. Public Health importance1. Nuisance• Large numbers flies can be bring significant nuisance by disturbing people during work and at leisure.• Flies soil the inside and outside of houses with their feaces.• They can also have a negative psychological impact because their presence is considered a sign of unhygienic conditions. 12
  13. 13. 2. Diseases• Flies can spread diseases because they feed freely on human food and filthy matter• Flies pick up disease-causing organisms while crawling and feeding• Those that stick to the outside surfaces of the fly may survive for only a few hours, but those that are ingested with the food may survive in the fly’s crop or gut for several days 13
  14. 14. Diseases that flies can transmit include entericinfections (such as dysentery, diarrhoea,typhoid, cholera and certain helminthinfections), eye Infections (such as trachoma) 14
  15. 15. • Triatomine Bugs (Order Hemiptera, Genus Triatoma)• Fleas (Order Siphonaptera) Human Flea (Pulex) Rat Flea (Xenopsylla) Cat Flea (Ctenocephalides) Jigger Flea(Tunga)
  16. 16. Bugs• Class: Insecta• Order: Hemiptera• Family: Cimicidae ( bed bugs )• Family: Reduviidae• Sub-family: Triatominae• 15 genera with > 100 spp• Panstrongylus, Triatoma, Rhodnius
  17. 17. Bed bugs• Family: Cimicidae• Blood sucking• Temporary ectoparasites of birds and mammals• Human parasites: – Cimex lectularis - main – Cimex hemipterus 17
  18. 18. Morphology• Oval, dorso-ventrally flattened, red-brown bodies• They are covered with short, stout hairs• They are 5-7mm long, with females slightly larger than males• Head have prominent compound eyes.• The proboscis is flexed backwards under the head when not in use• Legs terminate in a pair of simple claws• Forewings reduced (hemielytra pads), hind wings absent 18
  19. 19. 19
  20. 20. Habits• They feed at night on humans or other mammals• A blood meal is essential to production of eggs• Conceal themselves during the day in crevices of wooden beds, mattresses, or under loose wallpaper.• In search for hosts, they respond to warmth & CO2, odours 20
  21. 21. Habits...• Are easily transported in clothing and baggage• In cold weather they remain inactive in hiding places• They can survive starvation for over a year• Emit a characteristic odour from scent glands• Often found in dwellings with high rate of occupant turnover – hotels, motels, hostels, shelters & apartment complexes 21
  22. 22. Life Cycle• Females deposit about 200 eggs in cracks and crevices• Eggs – White, ovoid, about 1mm in length – Have an operculum at the anterior end – They are coated with transparent cement – They hatch in 4-10days – No hatching at 37⁰ or below 13⁰ C• Incomplete metamorphosis 22
  23. 23. Life cycle...• Nymph – Yellowish-white to brown – Passes through 5 or 6 moults before becoming a sexually mature adult• At 30⁰C, development from eggs to adult takes 3 weeks• The life span of the adult is 6-12 months 23
  24. 24. Medical Importance• Sleep disturbance• Biting nuisance – The bite produces red, itching wheals – Allergic symptoms – local or generalised urticaria and asthma• Transmission of diseases? – Not believed to be a vector of disease – As a mechanical carrier - Hepatitis B virus from human to human. Virus from faeces could infect a person by contamination of skin lesions or mucosal surfaces or by ingestion of dust 24
  25. 25. Triatomine bugsFamily: reduviidaeSub-family: triatominae• Cone nose/assassin/kissing bugs• Medically important, only found in americas• Size: 1-4 cm long• Elongated head• Lateral 4- segmented antennae• Eyes lateral
  26. 26. Tritomine bugs...• Proboscis ventrad• Two pairs of wings• Basal fore wing thick/hardened, posterior wing membrenous = heteroptera• Lateral margins of abdomen visible dorsally
  27. 27. Triatomine bugs…• Most are dull brown but some may have markings• The shape of the head, position of the antennae relative to the eyes: genera specific• Hemimetabolous• Eggs laid in/near host habitations: cracks on walls etc
  28. 28. Life cycle…• Eggs are laid in batches 100-800• Hatch into wingless nymphs• There are 5 nymphal instars, each requiring blood• N4 and N5 have rudimentary wings• May take in blood up to 10x body weight• Assassin?
  29. 29. Life cycle…• Both nymphs and adults feed nocturnally• Feed on exposed parts of the body: face, eyes, nose, mouth - kissing• Defecates during feeding• Feed on humans, wild and domestic animals.
  30. 30. Life cycle…• Development from egg to egg takes 3 months in lab but may take 1-2 yrs in nature• Vectors of T. cruzi:• R. prolixus, P. megistus, T. dimidiata and T. infestans• Prevention and control• Insecticide residual spraying, Insecticide treated bednets, improved housing
  31. 31. Order Siphonaptera• SIPHONAPTERA: Greek "siphon" (hollow tube) + "a" (without) + "pteron" (wing); fleas are wingless and have tube-like mouthparts for sucking blood• Body hard, laterally compressed, and bristly• Legs long with large coxae and 5-segmented tarsi• Generally live as ectoparasites of mammals and birds.• Fleas transmit various pathogens, including tapeworm and bubonic plague.• About 1,100 species of Siphonaptera in the world, 238 in North America.• 7 families of fleas based on characters of the head, abdomen, and various bristles. Many characters are visible only on specimens mounted on microscope slides.
  32. 32. Order Siphonaptera...Pulicidae -- common fleasIschnopsyllidae -- bat fleasTungidae -- sticktight and chigoe fleasDolichopsyllidae --rodent fleasHystrichopsyllidae -- rat and mouse fleasMalacopsyllidae -- malacopsyllid fleasVermipsyllidae -- carnivore fleas
  33. 33. Distribution• Species and genera are distributed in East-Asian, Central-Asian, West-American, Patagonian, Papuan (New Guinean), and East-African zoogeographical subregions.• Forest foothills with temperate and subtropical climate most favourable conditions for the fleas.
  34. 34. Morphology• Shape of the head, flat body & prehensile claws of legs help it to move easily through host’s wool• Length of jump some flea species attain ~32 cm, average body length being from 1 to 5 mm
  35. 35. Biology• Fleas are obligatory blood feeders parasitizing warm- blooded vertebrates. More than 94% of known species are parasites of mammals and only about 5% of them occur on birds• Fleas have 4 phases of development - the egg, the free- living larva, pupa and the imago• The larvae is wormlike, legless & eyeless with biting mouth parts. The larvae undergoes 3 instars. Prior to pupation it empties the alimentary canal, and spin a silken cocoon• The majority of fleas are closely associated with the hosts home (nest, burrow etc), attacking the host for feeding
  36. 36. Life cycle• Adult flea jumps onto a host, gets a meal. A flea bite becomes inflamed, itchy and swollen• Once fed, the flea will mate and lay eggs. This occurs in yards, houses, & on pets• In the next two to three weeks, hundreds of eggs will be laid in yard, house and on the host• Eggs hatch into small larvae, which feed on anything organic. Including dried blood, flea faeces, animal hair.
  37. 37. Life cycle...• The larva will feed for days, spin a cocoon and undergo metamorphosis• This stage is called the flea pupa. Its a worst stage because of its resistance to control• The cycle is completed when the flea pupa hatches out. Hatching occurs when a host is close, will bite and the cycle will start all over again
  38. 38. Medical significance• Fleas transmit pathogens that cause disease in humans and other animals. • The Cat and Dog flea are intermediate hosts for a tapeworm (Dipylidium caninum) that infects dogs, cats, and humans • The Rabbit flea spreads a myxomatosis virus within rabbit populations • Oriental Rat Flea is the primary vector of Yersinia pestis, the bacterial pathogen for bubonic plague.• The cat flea commonly infests dogs, dog flea may infest cats; both species may bite humans
  39. 39. Medical significance...• Sand flea/jigger, Tunga penetrans • Infect humans, pigs, birds • Adapted to intracutaneous attachment, larvae free living, adults free living but after mating penetrate the hosts. • Soft areas are preferred for penetration • In the body attaches with mouth, swells and envelops itself leaving a spiracle for breathing • Irritations start when a flea is mature, scratching helps to release eggs
  40. 40. Control• Best stage to control is an egg• Treating animal pets • If the pet is an inside animal, treat the home and the pet • If the pet is an outside animal, treat the pet & the area the pet has access to• Treat home areas when fleas suspected• Application of repellents• Keeping environments clean out of organic matter • Sweeping, mopping floors • Treating floors with insecticides; DDT, OPs, PY, Cb • Burning off infested soils• Flea trap to induce hatching of pupae
  41. 41. Control...• Wearing good, intact shoes• Daily inspection of areas of the feet (interdigital clefts)
  42. 42. Other ectoparasites Arachnid Vectors TICKS • Soft Ticks1. TICKS Class: Arachnida Soft Ticks (Ornithodorus) Order: Acarina Family: Argasidae Hard Ticks (Ixodes, Amblyomma, Genus: Ornithodorous Rhipicephalus, Dermacentor) General Characteristics -tough leathery integument2. MITES -flattened oval shape when examined(Dematophagoides, Demodex, dorsally Sarcoptes) -they lack the dorsal shield -they need to be examined ventrally to observe their capitulum or• Lice (Order Phthiraptera) mouthparts. – Head/Body Lice (Pediculus) Crab Lice (Phthirus) 43
  43. 43. Ticks• Ornithodoros spp. is the Ornithodoros populating in most important soft tick Europe, Africa, Asia and disease vector found Americas. throughout the world Life cycles • Soft ticks have a hemimetabolous life cycle, eggs hatching six legged larvae, which moult to eight legged nymphs 44
  44. 44. • There are 5 - 7 larval instars • The duration of the life cycle depending on the species depends on temperature, host availability and species• Each stage requiring a blood meal to proceed except of Disease Ornithodoros moubata • Soft Ticks are vectors for serious disease including : – Tick borne relapsing fever• Adult females lay small egg (Borrelia duttoni) batches following each blood – Rickettsial disease (Coxiella meal burneti), and some arboviruses 45
  45. 45. Hard Ticks• Class: Arachnida• Order: Acarina• Family: Ixodidae• Genus: Ixodes, Amblyomma, Rhipicephalus, Dermacentor 46
  46. 46. General Characteristics• They are flattened when examined dorsally• Characterized by the presence of a dorsal plate or scutum, and a capitulum that projects beyond the body outline• The scutum regularly covers the entire dorsal area• Ixodes spp. inhabit in Canada, Europe, Russia, China, Japan and Australia 47
  47. 47. • Ixodes Adult male showing the scutum covering the whole length of the body• The capitulum is seen protruding forward beyond the body outline 48
  48. 48. Life Cycle• Similar to that of Soft Ticks• There is only one nymph stage in Ixodes, and following several weeks of stasis the nymph will metamorphose into an adult 49
  49. 49. Diseases• Hard ticks transmit lyme disease, tick paralysis and Rickettsiae• Arboviruses that are responsible for encephalitis and haemorrhagic fevers, tularaemia and Babesia microti infection 51
  50. 50. Other medically important Hard Ticks • Dog ticksWood ticks (Rhipicephalus) found in(Dermacentor andersoni) coastal areas. • Lone Star ticks• Found in the (Amblyomma mountainous west of mericanum) found in North America; forests in SE USA • The females of these species causes tick paralysis. 52
  51. 51. • Dermacentor variabilis • Amblyomma, male hard tick. 53
  52. 52. • Both Dermacentor and Amblyomma transmit Rocky Mountain Spotted Fever (Rickettsia rickettsia).• Dermacentor transmit arboviruses responsible for encephalitis and heamorrhagic fevers.• D. variabilis is also responsible for spreading tularaemia, Mediterranean Spotted Fever and African Tick Typhus. 54
  53. 53. Control• Improve sanitation• Cementing floors to eliminate cracks and crevices and facilitate cleanliness• Where floors are not cemented should be kept out of dust• The floors and walls up to a height of about half a meter should be spread or dusted with lindane 55
  54. 54. • With dust floor monthly application would be necessary• Other chlorinated hydrocabons, organophosphorus compounds, carbomates or pyrethroids may be used 56
  55. 55. Mites• Class: Arachnida • General Characteristics• Order: Acarina • Dematophagoides, is a• Genus: Dematophagoides, common dust mite, inhabit beds, Demodex, Sarcoptes mattresses, carpets and house dust 57
  56. 56. • They are motile• They feed on residual organic debris 0.3 mm in length• They have four long legs, suckers and pincer chelicerae 58
  57. 57. • Dermatophagoides are antigenic, even when dead (fecal pellets are also allergenic)• Associated with complex allergies & symptoms such as asthma, conjunctivitis and dermatitis.• A treatment involves removal of accumulated antigens from mattresses and pillows 59
  58. 58. • Demodex have been implicated in dermatitis and should be considered in chronic, therapy-resistant cases of blepharitis (inflammation of eyelids)• The role of this mite in ocular disease is uncertain washing with soap and water is the most effective method of prevention. 60
  59. 59. • The mite, Sarcoptes scabiei, lives on human skin causes scabies• It is small (larger female is 0.3- 0.4 mm), colorless and oval with 8 short legs 61
  60. 60. • Symptoms of Sarcoptes infection arise after 4-6 weeks post invasion• Comprise a papular pruritic eruption at a site often unrelated to the site of infestation; symptoms of secondary infestations arise almost immediately 62
  61. 61. • Persistent nodular scabies involve itchy erythematous or scabbed nodules• When the immune system is impaired, Norwegian (crusted) scabies may develop – This presents with erythema and hyperkeratosis but little itching 63
  62. 62. Diagnosis• Discovery of mites or eggs by epidermal shave biopsy or superficial scraping• Burrows are best seen on wrists and inter-digital spaces• They fluoresce under a Woods lamp after application of liquid tetracycline and alcohol; alternatively ink may be used 64
  63. 63. Treatment and control• Lindane lotion is the treatment of choice, permethrin is another alternative• Ivermectin has been recommended for Norwegian scabies• Malathion liquid can also be used, benzyl benzoate is also active 65
  64. 64. • Malathion should be avoided in infants• Lindane should be avoided in pregnancy, breast- feeding and in young children• Treatment is applied over the whole body except the head and neck and washed off after 24 hours 66
  65. 65. • Normal laundering of bed linen and clothes is recommended• Household and sexual contacts should also be treated• Symptoms may continue after treatment because of persisting antigens, Calamine lotion may be used – other problems include re-infestation and secondary bacterial infection 67
  66. 66. Myiasis• Infestation of the organs and tissues of humans or animals by fly larvae that for some period of time, feed upon the living or dead tissues or the ingested food of the host• It is the condition in which larvae of flies exist as parasites in bodies of vertebrates
  67. 67. Myasis• Myasis is caused when fly maggots (larvae of dipterans) invade living tissue or when they are harboured in the intestines or bladder• Clinically, maggots causing myasis attack three parts of the bogy: Cutaneous tissue, body cavities and gut lumen
  68. 68. Myasis• Some spp of maggots cause subcutaneous myasis, invade sores &wounds (wound myasis), burrow under the skin (dermal myasis)• Body cavity myasis: Nasal myasis, ocular myasis ear myasis, myasis of the anus and vagina• Intestinal myasis-Eggs/larvae of many spp are deposited on food stuffs may survive the journey to intestinal tract. They may persist for months producing severe anxiety, and intestinal irritation
  69. 69. Myasis• Accidental = Facultative Myiasis• Obligatory Myiasis
  70. 70. Myasis• A number of families of flies e.g. Calliphoridae, Sarcophagidae and Oestridae are composed of flies that are have either facultative or obligate parasitic larval forms• Family: Calliphoridae • Non- metallic flies e.g. Cordylobia anthropophaga(Tumbu fly), Auchmeromya senegalensis (Congo floor maggot) • Metallic flies screw worms e.g. Cochliomya hominivorax(New World), Chrysomia spp (Old World) • Blow flies e.g. Lucilia spp (green bottles), Calliphora spp
  71. 71. MyasisFamily Sarcophagidae(Flesh flies) The two genera Sarcophaga and Wohlfahrtia are of medical importanceFamily OestridaeSubfamilies: Oestrinae, Gasterophilinae, Hypodermatinae and Cuterebrinae.Oestrinae, Gasterophilinae, Hypodermatinae are obligatory parasites of domestic animalsCuterebrinae has six genera that cause myasis in rodents, monkeys and livestock-Dermatobia hominis causes obligatory myasis in people and animals living in central and south America
  72. 72. Facultative Myiasis• Cutaneous myiasis - usually around wounds• Larvae normally found in meat or carrion occasionally adapt to a parasitic existence• Usually do not invade healthy tissues• Typically blow flies: species of Calliphora (bluebottles), Lucilia (greenbottles), Phormia, Sarcophaga and Wohlfahrtia (flesh flies), Cochliomyia macellaria (secondary screw-worm), and others
  73. 73. Forensic Entomology, 2001. Byrd and Castner, Eds.
  74. 74. Forensic Entomology, 2001. Byrd and Castner, Eds.
  75. 75. Forensic Entomology, 2001. Byrd and Castner, Eds.
  76. 76. Facultative Myiasis• Enteric Myiasis - accidental ingestion• 50 species reported - most Muscidae and Sarcophagidae• Passive transport of larvae - no development in host digestive tract• Severity depends on fly species, number, location• Genera commonly involved: Musca, Fannia, Muscina
  77. 77. Facultative Myiasis• Rectal/Urogenital Myiasis – access to intestine via anus; larvae feed on excrement• Immature stages may be completed in rectum or terminal part of intestine• Can occur in humans under unsanitary conditions• Primary genera - Fannia, Musca, Sarcophaga
  78. 78. Sarcophaga Species
  79. 79. Obligatory Myiasis• Calliphorids (non-metallic):⇒ Cordylobia anthropophaga - tumbu or mango fly (Africa); larvae attach and burrow into skin leaving spiracles exposed - boil-like swelling [cover with paraffin or oil to extract]⇒ Auchmeromyia senegalensis - Congo floor-maggot (Africa); adult looks like tumbu fly, but larvae do not remain attached; feed nightly from people sleeping on the floor
  80. 80. Obligatory Myiasis• Calliphorids (metallic):⇒ Cochliomyia hominivorax - New World screw-worm; eradicated from US and Mexico, but outbreaks possible⇒ Chrysomya bezziana - Old World screw-worm• Sarcophagids (flesh flies):⇒ Wohlfahrtia magnifica - ear, eye, nose• Oestrids (bot flies):⇒ Gasterophilus, Hypoderma, Oestrus, Cuterebra sp., and Dermatobia hominis (human bot fly)
  81. 81. Dermatobia hominis larva (human bot fly)
  82. 82. Control of Myiasis Species• Control or eradication of the fly population - through environmental sanitation or chemical control• Avoidance of infestation (mechanical control) - do not sleep outdoors or on the ground during fly activity, dress or cover wounds to avoid fly strikes, use screening• Treatment of infestation (remove larvae - antibiotic follow-up)

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