RESUMO
In Guadeloupe, during a general survey on intestinal schistosomiasis, the authors made a structural analysis of a limited focus of infection. The focus is formed by a river basin on the Carribean coast of Basse-Terre island. Sampling of the various elements of the parasitic cycle was done in spatial units defined by ecological and epidemiological criteria. The study of corresponding populations shows that: -- inside the twelve delimited sectors, only two include both hosts and parasites. They are zones with ditches and small temporary streams; -- the vector (Biomphalaria glabrata) density is always high in inhabited sectors; -- the rat, although present over the whole river basin, is only parasitized near inhabited places; -- fluorescent antibody level is an excellent indicator of the level of infection of human populations. Its variation can be detected in a time interval of less than one year; -- distance from contaminated water is one of the principal risk factors. A mathematical expression for this is given.