DISCUSSION

B. tenagophila, B. straminea and B. glabrata occurred only in Cantagalo. As observed by Paraense (1986) and Thiengo et al. (1998), B. tenagophila was the most frequent snail host species, as it occurred in all the surveyed localities.

The present paper also covers the distribution of both B. straminea and B. glabrata in the state of Rio de Janeiro (Figure). B. straminea was previously recorded in 14 municipalities (Paraense 1986, Thiengo et al. 1998, 2001) and the records for Cantagalo, Paraíba do Sul, Sapucaia, and Três Rios are new. B. glabrata has been previously recorded from Barra do Piraí, Duas Barras, Rio de Janeiro, and Sumidouro by Paraense (1972), but those for two districts of Cantagalo are new. The results of stool examination show that transmission is currently taking place in Duas Barras and Sumidouro, where the snail intermediate host is B. glabrata. This species is considered to be the most important host due to its widespread distribution and high susceptibility to infection by S. mansoni.

The distributional pattern of B. peregrina, considered a potential vector of schistosomiasis by Paraense and Corrêa (1973), has been extended to include Bom Jardim, Duas Barras, and Sumidouro. It was previously recorded in Barra do Piraí, Barra Mansa, Itatiaia, Nova Friburgo, Nova Iguaçu, Paraíba do Sul, Paulo de Frontin, Petrópolis, Resende, Sapucaia, Teresópolis, Três Rios, Valença, Vassouras, and Volta Redonda (Paraense 1966, Thiengo et al. 1998). B. schrammi was found only in Santa Maria Madalena, but was previously recorded in Cachoeiras de Macacu, Maricá, Nova Iguaçu, and São Gonçalo by Thiengo et al. (2001).

Of the remaining pulmonate species, the most frequently found was L. columella (43 districts), followed by P. marmorata (38 districts) and P. cubensis (31 districts). Specimens of an unidentified Lymnaea from Nova Friburgo resembled those described by Thiengo et al. (1998) from Teresópolis. Further anatomical studies of adult specimens from both municipalities are being undertaken to permit identification to species level. D. anatinum was found in 17 districts, followed by D. lucidum (11 districts), D. cimex (9 districts) and D. depressissimum (2 districts). D. anatinum was also the most frequent species in the Metropolitan Mesoregion according to Thiengo et al. (2001). The distribution of A. nordestensis, previously known in 13 municipalities in the state (Thiengo et al. 1998, 2001, Santos et al. 1999), is now extended to include Bom Jardim, Cordeiro, Santa Maria Madalena, São Sebastião do Alto, and Trajano de Moraes. The commonest Ancylidae species was G. ticaga as it was observed in the Metropolitan Mesoregion by Thiengo et al. (2001).

The Afro-Asian thiarid M. tuberculatus was found in 6 out of the 15 municipalities, in areas with dense populations inhabiting both polluted and non-polluted, lotic and lentic waterbodies. The most frequently found ampullariid was Pomacea sp. which is probably a new species.

The records of D. lucidum shedding echinostome cercaria and A. nordestensis shedding strigid cercaria are, respectively, the first and second records of these species acting as intermediate hosts of trematodes in Brazil.

Due to the limitation of logistic resources available to Funasa in the last years, the number of positive schistosomiasis cases are probably underestimated. The results of the stool survey in Duas Barras and Sumidouro indicate that transmission still goes on in these municipalities and both are recognized as low transmission sites.