To determine the effect of repeated, annual, age-targeted
therapy on prevalence and intensity of Schistosoma haematobium
infection in an endemic area, we treated all available, infected, school-age children (n = 2, 493) in the Msambweni area of Coast Province, Kenya with a randomized protocol of oral
metrifonate (10 mg/kg for three doses each year) or
praziquantel therapy (40 mg/kg as a single dose each year) for a period of one to three years. During 1984-1987, 1, 101 children completed three years of
therapy, 550 received two years, and 842 received a single year. Annual followup revealed significant long-term suppression of S. haematobium
infection in the targeted school-age population. Both cross-sectional analysis and study of individual outcomes suggested maximal suppression of
infection after two years of
therapy. Suppression lasted more than two years after
cessation of treatment, and was associated with reduced community transmission (gauged by decreased prevalence among new study entrants and decreasing negative-to-positive conversion on annual parasitologic examinations). Comparison of
metrifonate and
praziquantel outcomes indicated greater suppression of
infection and longer
infection-free intervals for some subgroups given
praziquantel. We conclude that annual population-based
therapy targeted to schoolchildren has direct and indirect beneficial effects for endemic communities. In some specific situations, repeat
therapy may not suppress transmission, and reduced
drug efficacy may be observed after one to three years, suggesting the need for additional non-drug control measures in highly endemic villages.