The influence of the susceptibility of the vector snails of S. mansoni on the development of the pathogenicity of the worm to the host was studied. Off-spring of snails Biomphalaria glabrata and Biomphalaria tenagophila were used, selected with regard to the susceptibility to S. mansoni of the strains BH and SJ trait, respectively. Parenteral, F1,F2, F3 and F4 generation cercariae were used for the infection of Swiss mice, which were killed eight weeks after infection. The number of eggs in the feces and the number of granulomas in the liver, spleen and intestines were counted. The size of the granulomatous reactions was evaluated. The results led to the conclusion that greater susceptibility of B. tenagophila was associated with a larger egg production in the feces and a higher density of granulomas in the liver. There is a clear inverse relationship between the area of hepatic, spleenic and intestinal granulomas and the rate of infection of the snails which served as intermediate hosts for the S. mansoni.
Schistosoma mansoni; Biomphalaria; Parasite egg count; Granuloma