The levels of infectivity of Schistosoma mansoni for the three species of Biomphalaria, intermediate hosts of parasite in Brazil were studied after exposing of molluscs to miracidia in the laboratory and in the field. The LE and SJ strains of S. mansoni, maintained in laboratory were used in these experiments as well as the WVS and RFS strains ohtained from faeces of schoolchildren from Belo Horizonte, MG. The results show the high level of infectivity of S. mansoni for B. glabrata with infection rates varying from 4.7 to 85-5%. The snail B. straminea was susceptible to LE, SJ and WVS strains, with infection rates of 11.0 to 24.6%, B. tenagophila was susceptible only to LE and SJ strains with infection rates of 2.5 to 6.5%. The mean number of cercariae of the WVS strain shed per day, by B. straminea and B. glabrata were 93 ± 59 and 782 ± 1,120, respectively.
Schistosoma mansoni; Infectivity; Snail hosts; Brazil