Swamp rice development, schistosomiasis, and onchocerciasis in Southeast Sierra Leone.

Seventy-four villages in eastern Sierra Leone, West Africa, many having a recently developed rice swamp, were surveyed for the presence of schistosomiasis and onchocerciasis, and their vectors. Prevalence rates for Schistosoma haematobium and S. mansoni were low, although the infections were widespread. There is some evidence that S. mansoni is extending its range in Sierra Leone although this is problematical because of the apparent absence of Biomphalaria pfeifferi, the recognized snail vector, from areas where the disease now occurs. The characteristics of rice swamp environment now being created in Sierra Leone are described and results of snail collections, which were with few exceptions small, are presented. Reasons for the apparent unsuitability of the developed rice swamp as a snail habitat are discussed. Onchocerciasis was found in all villages and the prevalence rate, almost 50%, was high. The rice swamp is not a suitable breeding site for Simulium damnosum s.l., but the study area is crossed by several major rivers and all villages in the area are within flying distance of potential breeding sites. There was no positive evidence that expansion of swamp rice farming will increase the incidence of water based/related diseases but a control program for onchocerciasis, which is a major rural health problem, would seem to be a national priority.