Control of Schistosoma mansoni transmission by chemotherapy in St. Lucia. II. Biological results.

Chemotherapy of all persons infected with Schistosoma mansoni was begun in Marquis Valley, St. Lucia, in March 1974. From January 1972 to the start of chemotherapy, the infection rate in field Biomphalaria glabrata collected in the valley was 1.09% (117/10,736) and the rate in sentinel B. glabrata was 1.48% (56/3,790). From March 1974 through December 1975, no infections were detected in either field snails (11,742 collected) or sentinel snails (3,230 exposed). The accumulated date suggest that, because of differences in topography and average annual rainfall, S. mansoni transmission occurs in this valley during the rainy season, whereas in other St. Lucian valleys under study it occurs during the dry season.