Endemicity, seasonality and focality of transmission of human schistosomiasis in 3 communities in southwestern Nigeria.

The pattern of transmission of human schistosomiasis was studied in 3 communities in southwestern Nigeria. The prevalence of Schistosoma haematobium in school children aged 5-16 years in the 3 communities was 76.2, 70.3 and 66.4%, respectively. The percentage of infected children harbouring heavy infections (greater than 50 eggs/10 ml urine) in the 3 communities was 75.5, 69.2 and 48.1% with a prevalence of visible haematuria among the heavily infected children of 29.5, 19.4 and 24.3%, respectively. Bulinus globosus, the snail host for S. haematobium, was found in all 7 sites sampled. The population density and the seasonal fluctuations in density and in prevalence of infection with S. haematobium differed markedly among the different sites. B. pfeifferi, the snail host of S. mansoni, was encountered in 2 of the 7 sites. The pattern of occurrence of infection with S. mansoni differed markedly between the 2 sites. The lack of consistency in the transmission pattern as regards both the seasonality and focality makes a thorough knowledge on the transmission pattern essential for the incorporation of community-based focal mollusciciding into the integrated approach to control of schistosomiasis morbidity in this ecological complex and highly endemic area.