Mosquitoes of Medical Importance in Sri LankaRumala MorelDept. of ParasitologyPeradeniya

Y2S2AedesAnophelesCulex

MEDICAL ENTOMOLOGYStudy of insects and other arthropods of medical importance

Insects: Mosquitoes, Flies, Midges, Lice, Bugs, Fleas Other arthropods: Ticks and Mites

Objectives:List the major mosquito borne diseases that occur globallyList the mosquitoes of medical importance in Sri Lanka indicating the diseases they transmitOutline the life cycle of a mosquito Describe the breeding & biting habits of the medically important mosquitoes in Sri Lanka Outline the strategies used for control of these 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 suggested transmission of malaria by mosquitoesbut no definite proof until end of 19th C1859- James Emerson Tennent in Ceylon: An account of the island.retiring punctually at sunset and sleeping under mosquito curtain is a valuable 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 in the vector- multiplication or development or bothSpecific time period necessary before vector can infect another host

Mosquitoes as vectors of disease:some important discoveries Patrick Manson- filarial parasites

Ronald Ross- malaria

Reed & team- yellow fever

1902 Graham- dengue

Aedes aegyptiDengue Dengue virusesChikungunyaChikungunya virusA.albopictusDirofilariasisDirofilaria repensMosquito borne diseases in Sri LankaMOSQUITODISEASEINFECTIVE ORGANISMAnopheles culicifaciesMalariaPlasmodium spp.Culex quinquefasciatusBancroftianWucheraria bancroftifilariasisC. gelidusJapaneseJap Encephalitis virusC. Tritaeniorynchus encephalitisC.pseudovishnuiYellow fever globally impt. mosq.borne diseaseNot found in SL

Biological characteristics influencingdisease transmission only females suck blood (blood required for egg maturation) breeding habits: preferred water type host preference anthropophilic- zoophilic blood sucking behavior- daytime/nightindoor/outdoor survival- 3-4 weeks (to allow development of pathogen) flight range- 0.5 - 1.5 km

Morphology of adult mosquito

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 mosquito with long palps = AnophelesA female with short palps = Culicine Anopheles mosquitoes rest and bite with their bottoms up @ 45 degree angle to the skin

Life span1 month 150-300 laid every 48-72 h4 stages1-3 weeks2-3 days2-3 daysMosquitoLife CycleWater is essential for breeding

Eggs:laid singly with floatsEggs:in clustersLarvae:parallel to surfaceno siphon tubeLarvae:siphon tube +Adult: rests @ 45 angle to surfaceAdult: rests parallel to surface

Aedes rests parallel to surfaceAnopheles culicfacies also rests parallel to surface like culex

Anopheles species of importance in Sri LankaAn. culicifacies- major vector of malaria

vectors 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 (man biting)- 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 high densities with rains (NE monsoon Oct-Jan)Intermediate zone: seasonal breedingWet zone: not normally found but breeding occur with failure of monsoons due to pooling in river bedsFound up to 900 m heightDistribution in Sri LankaAnopheles culicifacies

Rain water collections in pits, construction sites, hoof printsin dry zone

Stream/river bed pools; seepage pools at margins of lakes, reservoirs;open irrigation canal margins

Malaria vector breedingin quarry pits Kurunegala (NWP) andAnuradhapura (NCP)

Malaria vector breeding in Agro wellsMatale, Anuradhapura district

Wet zone- rock/sand river bed pools during droughts

pooling below dams/barrages

Kotmal oya- below dam

malaria vector breeding downstream of dams-An. culicifacies

Below dam at Nilambe oyaIlagolla- malaria outbreakdue to mosquito vectorbreeding in rock pools

Culicines- 20 generaIn Sri Lanka > 115 species

Culex Aedes Mansonia Armigeres

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 into Infective larvae L3 in 10-12 days and emerge from proboscis during the biteONLY development NO multiplication

Breeding sites of Culex quinquefasciatusStagnant, polluted water (sewage)

Culex quinquefasciatus breeding sites Dirty 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- paddy field breedersCx. gelidus- muddy pools husk pits

Japanese EncephalitisCulex gelidus

Vectors of Japanese encephalitis breed in paddy fields

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

Vectors of Dengue & ChickungunyaAedes aegyptiAe albopictusContainer breeders, clean water artificial- tyres, tin cans, plastic wasteIndoors- flower vases etc.Natural- cut bamboo stumps, leaf axils

SL: dengue endemic since 1989Transovarian transmission of arbovirusesAedes breeding sites

Aedes breeding in householdsindoorsoutdoors

Aedes Breedingoutdoors

Vector of Brugian filariasis& DirorfilariasisWater plants:PistiaEichorniaSalviniaMansonia spp.M uniformisM annuliferaBrown, speckled wings (light/dark scales)

Breeding: aquatic plantseggs laid in clusters on undersurface leaves of water plantsLarvae/pupae attached to plant roots

Armigeres subalbatusVery common dusk/night biterPest & vector of Dirofilaria repensBreeding: polluted waterDirofilariasisDirofilaria repens: common parasite of dogs

transmitted by Aedes, Armigeres, MansoniaCauses subcutaneous nodules in humans

Reduce mosquito densityPathogen control in humans Prevent man-mosquito contactControl of mosquito borne diseases

Reduce vector density 1Adult control Malaria control(1) Insecticide impregnated bed 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 other unused/unwanted containers. Eliminate breeding in standing pools of water Eg. air conditioners, refrigerators add surface oil layerClean birdbaths, vases, plant pots, rain barrels, kiddie pools etc. ONCE A WEEK

SummaryMosquitoes of Medical ImportanceAedesAnopheles culicfaciesCulex

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.