The effect of a control programme against Schistosoma mansoni on the prevalence and intensity of infection on an irrigated sugar estate in northern Tanzania.

On an irrigated sugar estate in northern Tanzania a control programme against Schistosoma mansoni was carried out during 1968-70. Through the routine use of molluscicides, the population of Biomphalaria pfeifferi snails was kept at a greatly reduced level. Concurrently a mass campaign was carried out to detect residents who were infected with S. mansoni so that they might be treated. The effect of these measures on the overall prevalence of the disease was measured by random studies before and after the mass diagnosis and treatment. The techniques used for mass diagnosis, for treatment, and for the prevalence studies are described, and the results of the control programme are presented and discussed. In the mass diagnosis campaign over 90% of the population were examined and 2 286 courses of treatment were administered to 1 922 persons. The combination of chemotherapy and snail control led to a significant reduction in the number of S. mansoni. infections. In field workers the prevalence was reduced from 59% in early 1969 to 31% in late 1970. In nonfield workers the reduction was from 36% to 15% and in the wives of employees from 28% to 14%. The main reasons why the prevalence was not reduced further were considered to be the failure of the drugs used to effect a complete parasitological cure and the inability of the mass diagnosis campaign to detect light infections. It was estimated that the overall reduction in the number of eggs released into the community as a result of the control programme was about 85%.