The impact of the local water-development programme on the abundance of the intermediate hosts of schistosomiasis in three villages of the Senegal River delta.

The populations of the potential intermediate hosts of Schistosoma mansoni and S. haematobium were studied for a year at transmission sites near three villages in the lower delta of the Senegal River. Biomphalaria pfeifferi, found to be widely distributed and increasingly abundant, appears to be well adapted to the new areas of irrigation (created by the dams at Diama and Manantali) thanks to its ability to withstand changes in temperature and to aestivate. This species is responsible for intense transmission of S. mansoni during the rainy season. In contrast, Bulinus globosus, the species responsible for the transmission of S. haematobium (which occurs during the dry season), had a more limited distribution. The changing distributions of these two snail species appear to be linked to changes in local ecology, themselves the result of the recent programme of water-development in the delta.