Development of Schistosoma mansoni in Biomphalaria tenagophila, Biomphalaria straminea and Biomphalaria glabrata

Abstract

Biomphalaria straminea snails from Argentina fail to shed cercariae even if exposed to high doses of Schistosoma mansoni EC miracidia. Alternative explanations for this failure are that miracidia are unable to penetrate the snail's epithelium or that the miracidia are killed by the snail's defense system. To discriminate between these 2 possibilities, B. straminea snails were individually exposed to increasing doses of miracidia. Susceptible B. glabrata were used as controls. Exposed snails were fixed 12 hr after exposure, and histological sections of the whole specimens were examined. Miracidia were seen to penetrate the epithelium of B. straminea and B. glabrata at similar rates (14.7%), independent of the exposure level. Regardless of the miracidial dose, 94% of the penetrating miracidia appeared encapsulated by the B. straminea defense system, whereas in B. glabrata, only 42% of the miracidia underwent encapsulation. These results show that resistance of B. straminea to S. mansoni EC strain is due to an efficient defense system that destroys miracidia once they have penetrated. FIGURE 1. Number of penetrating miracidia detected from sections of the whole snails at 12 hr after exposure as a function of miracidial dose. Points represent counts from individual snails. Differences between the regressions of B. glabrata and B. straminea were not significant. The intermediate hosts of Schistosoma mansoni in Amer-ica are, in order of increasing susceptibility, Biomphalaria straminea, Biomphalaria tenagophila, and Biomphalaria glabrata. 1 Differences in susceptibility of these snail species are strongly related to the capacity of their defense system to encapsulate and destroy the parasites. 2-5 Even though B. straminea and B. tenagophila are present in Argentina, there are no reports on the presence of S. mansoni in this country so far. 6 In our laboratory, we maintain a colony of B. stra-minea from the locality of San Miguel, Corrientes province, Argentina. Previous attempts to infect these snails with various doses of S. mansoni EC strain miracidia have failed. The EC strain was isolated in October 1981 by Lobato Par-aense from the feces of a resident of Picos, Piauí state, Bra-sil, where the vector of S. mansoni is B. straminea. 7 Experimental infections of B. straminea collected in this locality

Histopathologic features associated with susceptibility and resistance of biomphalaria snails to infection with Schistosoma mansoni

“…tenagophila and B. straminea from the State of Minas Gerais, Brazil, were individually exposed to 50 miracidia of S. mansoni (Souza et al 1995b. The strain used was the SJ-strain which is better adapted to B. tenagophila snails (Paraense & Correa 1981).…”

“…Differences in susceptibility/resistance occur not only intraspecifically (Souza et al 1995b), but have been demonstrated between different snail species, such as B. glabrata, B. tenagophila and B. straminea (Barbosa 1975, Souza et al 1995a.…”

Histopathological study on susceptible and resistant Bulinus truncatus snails to infection with Schistosoma haematobium

“…It must be emphasized that a nucleated cell layer of parasite origin never occurs outside the syncytial tegument of any sporocysts or redia when these occur in the molluscan tissue. The cell layer (primitive epithelium) which surrounds developing daughter sporocysts disappears before these leave the mother sporocysts (Meuleman et al, 1980;Southgate et al, 1989;Joubert et al, 1991;Souza et al, 1995;Lemos, 1999).…”

Short report: Schistosoma mansoni miracidia are killed by the defense system of an Argentine strain of Biomphalaria straminea.

“…1 Differences in susceptibility of these snail species are strongly related to the capacity of their defense system to encapsulate and destroy the parasites. [2][3][4][5] Even though B. straminea and B. tenagophila are present in Argentina, there are no reports on the presence of S. mansoni in this country so far. 6 In our laboratory, we maintain a colony of B. straminea from the locality of San Miguel, Corrientes province, Argentina.…”