Schistosoma mansoni in Pachwach, Nebbi District, Uganda, 40 years after Nelson.

Human- and snail-related aspects of the transmission of schistosomiasis mansoni was studied in the Amor Parish community located at the western bank of the River Nile in the Nebbi District, north-western Uganda. A cross sectional survey involving 642 people revealed an overall prevalence of infection among males and females of 81.6% and 81.3%, respectively. The prevalence of infection peaked in the 10-14 years age group, being 93.2% and 93.6% in males and females, respectively, but the prevalence remained high also in older age groups. Intensity of infection peaked in the 10-14 years age group in males and in the 15-19 years age group in females, reaching 768 and 482 eggs/g faeces, respectively. Intensity of infection diminished only to a moderate extent with increasing age with the infection intensity in the 40+ years age group being 270 and 241 eggs/g faeces in males and females, respectively. Observations on the human water contact pattern revealed a community having a very intensive water contact persisting into old age. Interviews revealed a high level of awareness of the disease schistosomiasis, and 87.2% had a history of passing blood in stool. The total set of observations point to intestinal schistosomiasis being of public health importance in Amor Parish. Studies on snail-related aspects of transmission revealed that Biomphalaria stanleyi was by far the most important snail host in the area. A tendency was seen for B. stanleyi snail numbers to be reduced during the rainy season.