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.