Effect of human immigration on the age distribution of schistosome infections in Siavonga community, Lake Kariba, Zambia.

A study on the distribution of schistosomiasis in the community at Siavonga revealed Schistosoma haematobium infection in 35.5% of 338 subjects and a geometric mean egg count (GMEC) and (s.d.) of 13.7 (7.2) eggs/10 ml urine. The prevalence of S. mansoni infection among 323 subjects was 60.1%, with a GMEC of 336.8 (4.8) eggs/g stool. Among the infected, 69.5% carried both schistosome species. Although prevalence of infection with either species was highest in those aged 10–14 years, high prevalences of infection were found in older age groups and egg intensities were uniformly distributed throughout all age-groups. The observed diversion from the typically age-dependent distribution of schistosome infections probably reflects exposure to infection relatively late in life, as the result of immigration from non-endemic areas.