Vector

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MSc Medical Parasitology Flashcards on Vector, created by tate0295 on 26/04/2015.
tate0295
Flashcards by tate0295, updated more than 1 year ago
tate0295
Created by tate0295 almost 10 years ago
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Question Answer
Extrinsic incubation Period (EIP) Time to infectioness in vector
Biological vectors Carry paths that multiply within vector and are transmitted usually by biting
Mechanical vectors Pick up paths externally and transmit by physical contact; Often require interrupted feeding or short time between moving from source of infection to place of transmission
Type I peritrophic matrix Stomach is a chitinous sack around blood meal in the mid-gut
Type II peritrophic matrix A continuous secreted tube through the midgut
Coxal fluid Secreted by ticks during biting; carries paths
Vector manipulation during infectiousness Probing behaviour of infected mosquitoes altered; Lower [apyrase] in saliva = increased clotting in host; means more probing required to feed = greater chance of transmission, esp. if seeking another host to complete blood meal
Mosquito borne disease
Mosquito mating Adult female mates soon after emergence - swarming; sperm stored in spermathecae to fertilise multiple batches of eggs; Anopheles males may insert plug into female to prevent further mating
Anopheline larval morphology No siphon - lie flat at water surface
Stegomyia larval morphology Shorter, darker siphon, with one pair of sub-ventral tufts
Culex larval morphology Longer, narrow siphon, with more than one pair of sub-ventral tufts
Mosquito pupal morphology Very similar between sub-genera; swim but don't feed; identification mainly by rearing to adults
Anopheles adults Head down, body up when feeding; Long palps with white banding; Male palps are club shaped
Culicine adults Head down, body level when feeding; Short palps; Male palps not club shaped
Temperature dependency for mosquito egg development Days in the topics; Weeks in temperate/arctic environments
Anopheles breeding and egg laying Typically found in open, sunlit water; Single eggs with floats; Dislike concrete &/or organic pollution in breeding sites, overgrown with vegetation; LIKE temporary, small pools of water - e.g. hoof prints after rains, flooded cultivation ridges; However, An. funestus prefer dense vegetation
Anopheles culcifaces Main vector in rural India and Sri Lanka; Occupies pools of stagnant water by streams/rivers - peak in dry season as water levels fall; Density dependent transmission - at low density, mainly zoophagic, so low transmission; Endophilic to easy to target with IRS
Anopheles stephensi Main urban vector in India; Breeds in large man-made containers, e.g. water tanks;
Anopheles dirus Major malaria vector in forests of SE Asia; Breeds in shaded pools; Highly efficient vector of MDR Plasmodium; Loggers and hunters at risk
Anopheles albimanus Malaria vector in S America; Breeds in water bodies broken with leaves of flotage; Active at night but may feed during the day; Weight of numbers vector; In dry season, can breed in brackish coastal lagoons
Anopheles darlingi Major malaria vector in Amazon; Habitats created by deforestation; streams, puddles, ponds
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Larval dipping With ladle; larval numbers per dip is a reliable measure of larval density and how well control is performing
Human landing catch Used to monitor number of bites per person, per day
CDC Light Traps Battery operated light lure; beside a bednet 1m above the ground; catches are proportional to human landing catch; Preferable method
Pyrethrum spray collections Cover all surfaces inside with sheets; Spray indoors to knock down mosquitoes for collection - good condition for dissection
Exit trap collection To catch mosquitoes exiting from windows during the night; Mosquitoes that bite indoors but then rest outside are caught - invulnerable to IRS
Pit trap collection Pit with side tunnels dug to trap outdoor resting Anopheles
Animal baited traps Animal under a net; to catch zoophagic Anopheles
Bednet collections Searching for mosquitoes resting indoors in the morning with a torch and pooter; only effective where the nets are untreated
Measuring adult survival Polovodova method - measuring dilations of ovaries; indicative of the number of times a femal has blood fed and become gravid; the older the female, the more likely to be infective
Horses for courses The choice of vector control methods depends on the setting - ecology, epidemiology, programmatic conditions
Adult vector control Most important, as has disproportionally large effect on vector potential (R0 and C - survival); IRS, ITN/LLIN - standardised, no need for adaption; Robust and broadly efective
Larval vector control Affects density only; Have to target most significant vector; Only if breeding sites are FIXED, FEW & FINDABLE; Must be closely adapted to local conditions
Vectorial capacity, C Daily rate of infectious bites per person; Most influenced by survival probability
Sporozoite rate The percentage of females that bear sporozoites in their salivary glands; Expressed as a percentage
Pare-Taveta Scheme Intervention 1954-1959; effect of IRS on malaria transmission; Massive fall in infant infection, but did not quite reach 0, so deemed a failure
Increasing insecticide resistance and reduced development Resistance is increasing, but new active compounds are not being developed; Mostly for agriculture, which is not safe for IRS; Pyrethroids (1970s) are still the best option
Attacking adult vectors with ITNs Insecticide can restore effectiveness of a net with holes; Gives 2x protection vs untreated; Easier - much less insecticide (than IRS), less training, less often; Also contribute to mass effect protection
Long lasting insecticides for nets Compounds can now last longer than the lifetime of the net; Can be applied as a coating or incorporated into material; Selling as second hand - can people tell if they are (still) treated?
ITNs and child mortality Even where children do not develop immunity due to exposure, there is no rebound in mortality, as long as net usage remains; However, younger children are more likely to be covered than older children
ITN/LLIN vs IRS Similar impacts on malaria; LLIN longer lasting, less logistically challenging; IRS campaigns can fail unless well planned and implemented - nets can be simply given out; IRS needs to occur once or twice per year - LLINs may last 3 years
Choosing ITN/LLIN or IRS Based on feasibility and sustainability on large scale; IRS advantages against highly seasonal, unstable or epidemic malaria - extremely effective for a few months, rapid response
Sandfly oviposition Eggs laid in damp sites with organic material - makes control at breeding sites difficult; 4 instars; Immature stages very rarely seen in field
Adult feeding Both sexes feed on sugar sources; Females take blood meal for ovarian development; Pool feeders; Host choice varies by species; Endo- or exo-pahgic; Have stomodeal valve to prevent bloodmeal back-flow; Bloodmeal straight to mid-gut
Sandfly dispersal Are weak flyers; 'hopping' flight; low dispersion - few hundred metres; Means Leishmania tends to be focal
Sandflys as human vectors 2 genera are human vectors - Phlebotomus (Old world) and Lutzomyia (New world); +70 species transmit parasite
Leishmania development in Sandflies Sandfly egg to adult - 4 weeks; Amastigotes ingested and multiply; Procyclics develop into nectomonads escape PM and attach to mid-gut; Develop into nectomonads that reproduce; Develop haptomonads and metacyclics; Migrate to stomodeal valve
Factors effecting sandfly control Zoonosis vs anthroponosis; One or many reservoirs; Resting/breeding sites scattered or concentrated; Endo or exo phagic; Endo or exo philic; Insecticide resistance
Vector control of zoonotic leishmaniasis in humans IRS/ITN can be effective if sandflys are endophilic, transmission is domestic, if main reservoir is common around household; Can target the main reservoir - dogs, rodents, cows etc.
Deltamethrin-impregnated nets reduce human landing rates of L. longipalpis in Amazon households >50% bites indoors; Most biting occurs when children are under nets; ITNs reduced landing rate by 80%; ITNs killed 98% flies inside houses
Effect of insecticide-impregnated dog collars on incidence of zoonotic VL in Iranian children Reduce the odds of infection by 61% in dogs and 535 in children; Collars could have a role in control and replace dog culling in some places; Effectiveness depends on importance of wild versus domesticated canids
Rodent control for Sandfly control Destroy rodent burrows - potential laying sites for sandflies
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