Irrigation, schistosomiasis, and malaria in the Logone Valley, Cameroon.

Field studies of a rice irrigation project in Mayo-Danai, North Cameroon permitted a direct comparison between pre- and post-development data relating to schistosomiasis and malaria infection. A stratified sample of 4,000 inhabitants, representing 8% of the population living in 28 areas at the time of the first survey, was investigated 5 times between 1979 and 1985. Due to the significant population increase since 1982, 1,500 persons were added to the initial sample. The prevalence of schistosomiasis and malaria remained constant over the 6 years. No changes in the transmission sites were observed. Malacological investigations showed a decrease in the snail population in the project area. Sanitation activities (i.e., drain cleaning and well construction) and decreased rainfall contributed to this situation. The prevalence of infection among the migrants was low. High prevalence of schistosomiasis was found only in villages located along a previously contaminated temporary river.