Schistosomiasis around Siavonga, on the shores of Lake Kariba, Zambia.

A schistosomiasis prevalence survey was carried out at Lake Kariba, Zambia--only the second since the creation of the lake more than 30 years ago. In the 20 or so years since the first study the prevalence of Schistosoma mansoni has increased from 16% to 56% while that of S. haematobium has dropped from 69% to 17%. There was variability in the infectivity of contact sites (P < 0.001) and this had an impact on prevalence. In contrast, sex, age (within the range 5-19 years), residential area (distance from the lakeshore) and activity at the contact site had no significant effect on prevalence (P > 0.05). The population at Matinangala was more at risk of infection by both S. haematobium (P < 0.001) and S. mansoni (P < 0.05) than the Siavonga population. Both Biomphalaria pfeifferi and Bulinus globosus were present in the area and factors which may be influencing their distribution are discussed.