Since 1986, several outbreaks of malaria have occurred in the traditionally non-mal;rious areas. These were related to hydrological changes below dams causing pooling in the rocky and sandy river bed linked with water diversion and aggravated by droughts. In addition human migration between the downstream settlements and upper non malarious areas promoted parasite carriage.
Infection is associated with prolific breeding of the vector in blocked drains, sewage pits and polluted stagnant water collections that are common in the poorly planned urban environment. such sites also favour breeding of Armigeres mosquitoes.
the outdoor agricultural lifestyle and rural dwellings carry high risks of man-mosquito contact.
The global emergence of dengue fevers as an urban public health problem is associated with Aedes breeding. Modern lifestyles with widespread use of 'thowaway containers that end up in refuse are ideal breeding sites. 90% of Aedes breeding in in Sri Lanka occur in discarded receptacles, empty coconut combs and used tyres made use of for varying purposes.
Rumala MorelDept. of ParasitologyPeradeniyaY2S2Mosquitoes of MedicalImportance in Sri LankaAedesAnophelesCulex
MEDICAL ENTOMOLOGYStudy of insects and otherarthropods of medical importanceInsects: Mosquitoes, Flies, Midges,Lice, Bugs, FleasOther arthropods: Ticks and Mites
Objectives: List the major mosquito borne diseasesthat occur globally List the mosquitoes of medical importancein Sri Lanka indicating the diseases theytransmit Outline the life cycle of a mosquito Describe the breeding & biting habits ofthe medically important mosquitoes in SriLanka Outline the strategies used for control ofthese mosquito species in Sri Lanka
Anophelines-AnophelesMosquitos – found globally in all climates>3000 spp. only few of medical importance Culicines - Culex- Aedes- Mansonia- Armigeres
Role of mosquitoes in disease transmission2500 yrs ago Susruta suggestedtransmission of malaria by mosquitoesbut no definite proof until end of 19thC1859- James Emerson Tennent in‘Ceylon: An account of the island’….retiring punctually at sunset andsleeping under mosquito ‘curtain’ is avaluable prophylactic against fevers…
Medical importance of Mosquitoes biting nuisance- pests/allergy vectors of diseasetransmit disease causing organismsMosquitoes as biological vectorsEssential part of the life cycle takes place inthe vector- multiplication or developmentor bothSpecific time period necessarybefore vector can infect another host
Mosquitoes as vectors of disease:some important discoveries1878 Patrick Manson- filarialparasites1897 Ronald Ross- malaria1900 Reed & team- yellow fever1902 Graham- dengue
Aedes aegypti Dengue Dengue virusesChikungunya Chikungunya virusA.albopictus Dirofilariasis Dirofilaria repensMosquito borne diseases in Sri LankaMOSQUITO DISEASE INFECTIVE ORGANISMAnopheles culicifacies Malaria Plasmodium spp.Culex quinquefasciatus Bancroftian Wucheraria bancroftifilariasisC. gelidus Japanese Jap Encephalitis virusC. Tritaeniorynchus encephalitisC.pseudovishnuiYellow fever – globally impt. mosq.borne diseaseNot found in SL
Biological characteristics influencingdisease transmission only females suck blood (blood required foregg maturation) breeding habits: preferred water type host preference – anthropophilic- zoophilic blood sucking behavior- daytime/nightindoor/outdoor survival- 3-4 weeks (to allow development ofpathogen) flight range- 0.5 - 1.5 km
SEX DETERMINATION - AntennaClassification of mosquitoes -1. SEX"plumose" (hairy) - male"pilose" (not very hairy)female
Palps (sensory organs just lateral to the proboscis)Classification of mosquitoes – 2. GENERAA female mosquitowith long palps = AnophelesA female withshort palps =CulicineAnopheles mosquitoesrest and bite with theirbottoms up @ 45 degreeangle to the skin
Life span1 month150-300laid every 48-72 h4 stages1-3 weeks2-3 days2-3 daysMosquitoLife CycleWater isessentialfor breeding
Aedes rests parallel to surfaceAnopheles culicfacies alsorests parallel to surface like culex
Anopheles species of importance in Sri LankaAn. culicifacies- major vector of malariavectors of minor importanceAn. subpictusAn. annularisAn. vagusAn. tesselatusMajor vectors in other countriesAn. gambiae- vector of human malaria andBancroftian filariasis in Africa
Characteristics of importance for a malarial vector density longevity biting habits- anthropophilic (manbiting)- outdoor/indoornight biting mosquitoesKeys/charts used for species identificationRests on walls – Indoor Residual SprayingEffective control method
Anopheles culicifaciesDistribution: Sri Lanka, India, MyanmarPakistan, Middle East, Nepal, ThailandAdult: small- mediumwings & female palps - bandingresting position culicine-likeBreeding: shallow, sunlit, clear fresh waterEg. Edges of slow flowing streams/rivers;rain water collections in ground pools and pits
Dry zone: endemic speciespresent throughout year but highdensities with rains (NE monsoon Oct-Jan)Intermediate zone: seasonal breedingWet zone: not normally found but breedingoccur with failure of monsoons due topooling in river bedsFound up to 900 m heightDistribution in Sri LankaAnopheles culicifacies
Rain water collections in pits,construction sites, hoof printsin dry zoneStream/river bed pools;seepage pools atmargins of lakes,reservoirs;open irrigation canalmargins
Culex quinquefasciatusVery common urban domestic mosquito throughoutSouth/SE Asia- vector of bancroftian filariasisSmall, brown, absence of markingsBreeding: eggs in rafts (75-100 eggs)highly polluted (organic matter) stagnant watereg. blocked drains, cess pits, waste water pitsHabits: night biter, outdoor/indoorbites man, cats/dogsRests in shade eg. indoors in dark cornersclothes, under furniture etc.
Culex quinquefasciatus Biological vectorLymphatic filariasis:Microfilaria ingested with the blood meal develop intoInfective larvae L3 in 10-12 days and emerge fromproboscis during the biteONLY development NO multiplication
Breeding sites of Culex quinquefasciatusStagnant,polluted water(sewage)
Culex quinquefasciatus breeding sitesDirty water in blocked drains, cess pits etc.
Culex tritaeniorhynchusCx. gelidusCx. pseudovishnuiBreeding: paddy fields, marshes,husk-soakage pitsHabits: night, outdoor/indoorbites animals; pigs/cattle(zoophilic)Vectors of Japanese encephalitis
Japanese encephalitis:Epidemiological cyclePigs important amplifier hostsMosquito vectors:Cx. tritaeniorhyncus;Cx.pseudovishnui- paddyfield breedersCx. gelidus- muddy poolshusk pits
Vectors of Japanese encephalitis breed in paddy field
Aedes spp.Ae. aegypti Ae. albopictusSmall, delicate, black & white banding on legs.wings clearVectors of-Dengue fever, Chikungunya, Dirofilaria repensYellow fever (not in Sri Lanka)Breeding: eggs laid singly (no floats)damp surfaces that get submergedrain water collections in containers
Vector of Brugian filariasis& DirorfilariasisWater plants:PistiaEichorniaSalviniaMansonia spp.M uniformisM annuliferaBrown, speckled wings (light/dark scales)Breeding: aquatic plantseggs laid in clusters on undersurfaceleaves of water plantsLarvae/pupae attached to plant roots
Armigeres subalbatusVery common dusk/night biterPest & vector of Dirofilaria repensBreeding: polluted waterDirofilariasisDirofilaria repens: commonparasite of dogstransmittedby Aedes,Armigeres,MansoniaCauses subcutaneousnodules in humans
Reduce mosquito densityPathogen control in humansPrevent man-mosquito contactControl of mosquito borne diseases
Reduce vector density 1Adult control – Malaria control(1) Insecticide impregnatedbed nets – treat every 6/12(2) Indoor Residual Spraying
Reduce vector density 2Eliminate breeding sitesDestroy larvaeAedes spp.• Properly dispose of old tires, cans, bottles,water-collecting rubbish, and otherunused/unwanted containers.• Eliminate breeding in standing pools of waterEg. air conditioners, refrigerators – add surfaceoil layer• Clean birdbaths, vases, plant pots, rainbarrels, kiddie pools etc. ONCE A WEEK