Selective primary health care: strategies for control of disease in the developing world. I. Schistosomiasis.

The control of schistosomiasis should be related to its unique biology and ecology. Whereas schistosomes multiply within the snail intermediate host, they do not replicate within the mammalian definitive host. As a consequence, a large proportion of infected humans have low or moderate worm burdens, the disease tending to occur in the small proportion of individuals harboring large numbers of worms. This situation suggests an unusual strategy: the control of schistosomal disease rather than the usual approach of control of infection and its almost invariable end point of eradication. Control of infection (transmission) requires use of mollusciciding, provision of water supplies and sanitation, health education, and chemotherapy and is still highly unlikely to result in eradication. Control of disease can be achieved at far lower cost by chemotherapy alone using the newer single-dose, oral, nontoxic chemotherapeutic agents.