Eradication of a Sylvatic Focus of Schistosoma mansoni Using Biological Control by Competitor Snails

The Grand Etang Lake on the island of Guadeloupe (West Indies) is a sylvatic focus for Schistosoma mansoni Sambon, 1907, characterized by surrounding populations of heavily infected Rattus rattus Linne, 1758, a low infection rate of an intermediate snail host, Biomphalaria glabrata (Say, 1818), and the absence of permanent human residents. In 1976, the prosobranch snail Ampullaria glauca (Linne, 1758) was accidentally introduced into the lake and caused a strong regression of the floating plant Pistia stratiotes L., which constituted the habitat of B. glabrata. Concomitantly, a rapid decline of murine schistosomiasis took place, and the parasite completely disappeared from around the lake by 1985. In 1987, a resurgence of the parasite was observed and a competitor/predator snail, Marisa cornuarietis (Linne, 1758), was introduced into the lake. Colonization by M. cornuarietis was rapid, and by 1989, the remaining associated P. stratiotes/B. glabrata colonies were eliminated, as was the S. mansoni infection in rats. Sampling carried out in 1990 and 1991 confirmed the eradication of both the snail host and its parasite. (C) 1991 Academic Press, Inc.