[Epidemiological study of schistosomes in a coastal lake of recent formation]

Parasitological and malacological surveys were conducted round a fresh water lake, previously a salted lagoon, in the South of Bénin and leaded to measure prevalence of schistosomiasis. 23 percent of population were found positive for Schistosoma haematobium and 13.4 percent for S. mansoni. Prevalences were different from locality to locality according to beach variations, but mean of parasite density was quite constant. Males were significantly more infected than females and young adults were more infected than children or old individuals. The prevalence distribution among people could be explained by behaviour and occupations. Five gastropod species were collected from which 2 are well known as intermediate host of S. haematobium (Bulinus globosus) and S. mansoni (Biomphalaria pfeifferi). A third species (Bulinus forskalii) which could be involved in S. haematobium transmission was found. Specimens of Bulinus were generally few and more represented in dry season. B. pfeifferi was more abundant especially at the end of rainy season. Populations of these 3 species were more dense by silty or swampy sides with shrub vegetation and poor oxygenated, acidic water rich in organic materials.