RESUMEN
A comparative histopathological study of three snails species - Biomphalaria glabata, B. tenagophila and B. straminea - which had been infected with Schistosoma mansoni miracidia reveled similar qualitative features, consisting of areas of sporocyst proliferation and differentiation associated with reactive host reaction, at the time they were actively eliminating great number of cercariae. However, in specimens that were exposed to miracidia but failed to eliminate cercariae later on, different histopathological pictures were observed in different snail species. While B. glabrata exhibited frequent focal (granulomatous) proliferation of amebocytes in several organs, B. tenagophila and B. straminea only rarely showed such reative changes, suggesting that the mechanism of resistance to miracidial infection probably follows different pathways in the snail species studied.