Changes induced in Biomphalaria glabrata (Say, 1818) following trials for artificial stimulation of its internal defense system

Biomphalaria glabrata can react through different pathways to Schistosoma mansoni miracidium penetration, according to the degree of resistance/susceptibility presented by different snail strains, which is a genetically determined character, resistance being the dominant feature. However, it has been observed that previous susceptible snail strain may change its reactive behavior along the course of infection, exhibiting later a pattern of cercarial shedding and histopatopathological picture compatible with high resistance. Such observation suggests the possibility of B. glabrata to develop a sort of adaptative immunity face a schistosome infection. To explore on this aspect, the present investigation looked for the behavior of S. mansoni infection in B. glabrata previously subjected to different means of artificial stimulation of its internal defense system. Snails previously inoculated with irradiated miracídia (Group I); treated with S. mansoni antigens (Group II) or with a non-related parasite antigen (Group III) were challenged with 20 viable S. mansoni miracidia, and later looked for cercarial shedding and histopathologic changes at different times from exposition. Nodules of hemocyte accumulations were found at the site of antigen injection. These nodules resembled solid granulomas, and were larger and more frequent in snails injected with S. mansoni products as compared to those injected with Capillaria hepatica. However, the presence of such granulomas did not avoid the S. mansoni challenge infection from developing in a similar way as that seen in controls. The data are indicative that hemocytes are able to proliferate locally when stimulated, such capacity also remaining localized, not being shared by the population of hemocytes located elsewhere within the snail body.

Behavior of Schistosoma mansoni-induced histopathological lesions in Biomphalaria glabrata submitted to ionizing radiation

O presente trabalho demonstra que a irradiação repetida, num total de 15.000 rads, resulta numa rápida supressão da eliminação das cercarias em caramujos infectados pelo Schistosoma mansoni. Inicialmente os esporocistos desaparecem dos tecidos. As formas evolutivas das cercarias são mais resistentes e apresentam vacuolização citoplasmática e condensação nuclear antes de desaparecerem. Não foram observadas reações nos tecidos do hospedeiro. Trinta e quatro dias após a última irradiação, os caramujos voltam a eliminar cercárias. Numerosos esporocistos e cercárias em desenvolvimento aparecem infiltrando difusamente os tecidos à maneira de uma neoplasia maligna, sem sinais de oposição da parte do hospedeiro, a qual era visível nos controles infectados e não irradiados. A região do ovo-testis apareceu destruída após a radiação, mas retornou à sua aparência normal em torno de 40 dias mais tarde. A radiação ionizante afeta tanto o hospedeiro como as formas em desenvolvimento do parasito, mas estas alterações impressionantes são logo reversíveis.

Comparative histopathology of Biomphalaria glabrata, B. tenagophila and B. straminea with variable degrees of resistance to Schistosoma manzoni miracidia

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.