Microgeographical and tribal variations in water contact and Schistosoma mansoni exposure within a Ugandan fishing community.

Objective: To explore patterns of water contact and Schistosoma mansoni exposure by age, sex, tribe and space within a single village.

Methods: For 10 months, we systematically observed water contacts made by the 800 inhabitants of a small Ugandan fishing village. In order to estimate cercarial exposure, times spent in water were weighted by snail infection levels, time of day and degree of immersion.

Results: There were marked differences in water contact patterns between the two main tribes, which inhabited geographically distinct ends of the village resulting in geographically distinct spatial patterns of water contact. The distributions of the intermediate hosts, Biomphalaria sudanica and Biomphalaria stanleyi, also appeared to differ over small distances. This led to quite different exposure patterns between the two tribes, particularly amongst females.

Conclusions: Schistosoma mansoni exposure can vary markedly within a single village. Such non-homogenous patterns of exposure are likely to have wider implications for schistosomiasis control programmes and research studies.