Molluscan response to parasite: Biomphalaria and Schistosoma mansoni interaction

Abstract

Digenetic trematodes use molluscs, almost always a Gastropoda, in their evolutive cycle, as
intermediary hosts. The genus Schistosoma, with three main species that infect humans - S. mansoni,
S. japonicum, and S. haematobium – shows a prevalence of 200 million patients in various countries
worldwide, and 600 million people are still at risk of infection. S. mansoni is the most prevalent
species, and Biomphalaria snails are its intermediary hosts. Although the campaigns of
schistosomiasis control based on chemotherapy have reduced the morbidity and prevalence of this
disease, transmission continues in almost all the areas submitted to intervention. One of the factors
that has influence on the susceptibility of Biomphalaria to S. mansoni infection is ability of the host
internal defense system (IDS) to recognize and destroy the parasite. In Biomphalaria, the IDS is
composed of cellular elements named hemocytes that act jointly with soluble components present in
hemolymph, which could affect directly the larvae, or act in the recognition of the parasite, and
activation of hemocytes. The susceptibility level of the mollusc has been attributed to the hemocyte
capacity of involving and destroying the parasite, and this will be the centre of interest of this review.
The study of S. mansoni and Biomphalaria interaction in resistant snail strains is important not
only due to the academic-scientific value of this fascinating research area, but also to the potentially
possible alternatives for the control of this endemia.