Control of schistosomiasis in the new Rahad Irrigation Scheme of Central Sudan.

As the new Rahad Irrigation Scheme in Central Sudan began its first agricultural season in 1978, the Blue Nile Health Project was being developed to prevent schistosomiasis and other water-associated diseases in the Rahad and Gezira-Managil schemes. Taken as an indication of overall transmission in the Rahad scheme, the prevalence of infection among children in the newly established schools was found initially to be 14% for Schistosoma mansoni and 1% for Schistosoma haematobium in 1980. In the older Gezira-Managil irrigation system nearby, where transmission had not been controlled there was also little S. haematobium but the prevalence of S. mansoni in school-aged children was rising above 70%. To avoid a similar future in the Rahad scheme an integrated control strategy was implemented in 1980 using chemotherapy and snail control, supported by safe water supplies in every village. Under this strategy the prevalence of S. mansoni in the schoolchildren was reduced below 10% by 1983 at an annual cost of less than $4 per capita, about $300 per square kilometer. S. haematobium remained at 1% in the schoolchildren in 1983. The major cost was for village water supplies with about 20% of the total going for snail control and 10% or less for chemotherapy. Over a third of the cost was for equipment and supplies purchased abroad, requiring hard currency. Economically feasible prevention of transmission in the long-term will require reduction of the annual cost to about $1 per capita. Cost reductions should be made primarily in operation and maintenance of the water supply systems and in snail control.