The aim of the current paper was to study in the state of Sergipe the population distribution and interactions between two species of Biomphalaria, the snail vectors of Schistosoma mansoni in the northeastern Brazil. Data collected in 1969 showed that B. straminea, with only one exception, was limited to the semi-dry region, while B. glabrata was found to live exclusively in the forest region, both in the state of Sergipe. This spatial distribution seemed to suggest that the above Biomphalaria species used to dominate specific territories. Snail collections made in 1988 in the same 37 places searched in 1969, showed that B. straminea has invaded territories previously occupied by B. glabrata, suggesting that a process of competitive displacement is taking place between these two closely related species. Natural snail infection rates were determined and some ecological aspects of the snail breeding places were registred.
geographical distribution; competitive displacement; mollusca; Planorbidae; Biomphalaria; schistosomiasis transmission