Divergent Effects of Exposure on Intermediate-Host Snail Species and from Coastal Kenya.

Abstract infection causes urogenital schistosomiasis, a chronic inflammatory disease that is highly prevalent in many parts of sub-Saharan Africa. Bulinid snails are the obligate intermediate hosts in the transmission of this parasite. In the present study, and snails from coastal Kenya were raised in the laboratory and exposed to miracidia derived from sympatric specimens to assess the species-specific impact of parasite contact and infection. The snails' subsequent patterns of survival, cercarial shedding, and reproduction were monitored for up to 3 months postexposure. exposure significantly decreased the survival of , but not of . Although both species were capable of transmitting , the study population had a greater cumulative incidence of cercarial shedders and a higher average number of cercariae shed per snail than did the population. The effects of prior parasite exposure on snail reproduction were different between the two species. These included more numerous production of egg masses by exposed (as compared with unexposed snails), contrasted to decreased overall egg mass production by parasite-exposed . The interspecies differences in the response to and transmission of reflect clear differences in life histories for the two bulinid species when they interact with the parasite, which should be taken into account when planning control interventions aimed at reducing each host snails' contribution to local transmission of infection.