Compatibility of Schistosoma mansoni and Biomphalaria pfeifferi in Northern Senegal

The construction of the Diama dam on the Senegal River and the ensuing ecol ogical changes have led to a massive outbreak of Schistosoma mansoni infect ion in Northern Senegal, associated with very high intensity of infections, due to extremely intense transmission. The vectorial capacity of Biomphala ria pfeifferi from Ndombo, near Richard-Toll was investigated in order to a ssess the role of the snail-parasite relationship in this particular epidem iological situation. The results revealed an unusually high compatibility b etween the Senegalese S. mansoni strain and its local snail intermediate ho st, B. pfeifferi The snail infection rate after exposure to a single miraci dium per snail was 87 %. The cercarial production of infected snails was ve ry high, with a mean total production of 50456 cercariae per snail. No sign ificant difference was found in the total cercarial output between snails e xposed to 1 miracidium and those exposed to 5 miracidia. The increase in th e rate of cercarial output was significantly greater in snails exposed to 5 miracidia, but there was a higher mortality in this group. The chronobiolo gical cercarial production pattern showed a peak around mid-day. The implic ations of these findings on the epidemiology of schistosomiasis in Northern Senegal are discussed.