The effect of repeated targeted mass treatment on the prevalence of schistosomiasis mansoni and the intensity of infection in Machakos, Kenya.

In a valley in Machakos District, Kenya, the entire population was surveyed in 1976 for the presence and number of eggs of Schistosoma mansoni in their faeces. All persons with 300 or more eggs g-1 faeces were then treated with a single dose of hycanthone, 1.5 mg kg-1 body-weight. A re-survey was carried out in 1977, followed by the treatment of all persons with 200 or more eggs g-1 faeces. After another re-survey in 1978, all persons with 100 or more eggs g-1 were treated. The final survey was carried out in 1981. It was found that the treatment of persons with a high egg output had a pronounced effect on the intensity of infection in the total population, but that, after a first considerable drop in the prevalence rate, further decreases were much smaller. Continuing moderate prevalence rates in very young children were an indication of continuing transmission.