Description of the adult worms of a new Brazilian isolate of Echinostoma paraensei (Platyhelminthes : Digenea) from its natural vertebrate host Nectomys squamipes by light and scanning electron microscopy and molecular analysis

Echinostoma paraensei Lie and Basch, 1967 (Echinostomatidae:Platyhelminthes ), a 37 collar spine echinostome of the "revolutum group", has been used ex tensively as a model organism to study the interactions of digenetic tremat odes with both their snail and vertebrate hosts. This worm was first isolat ed from the snail Biomphalaria glabrata from Belo Horizonte (BH isolate), M inas Gerais State, Brazil, by Lie and Basch [J Parasitol (1967) 53:1192-119 9]. The natural definitive host for the BH isolate was never determined, an d it has been maintained in the laboratory since 1967 in B. glabrata and ha msters. In this study, using light and scanning electron microscopy and mol ecular analysis, we describe an echinostome recently obtained from its natu ral vertebrate host, the wild rodent Nectomys squamipes (Rodentia: Sigmodon tinae) from Sumidouro, Rio de Janeiro State, Brazil (RJ isolate). This echi nostome was also compared to the laboratory-maintained BH isolate of E. par aensei. We observed that adult worms of both BH and RJ isolates could be di fferentiated from other echinostome species by the relatively small size of the dorsal collar spines relative to lateral and corner collar spines. SEM confirmed the similarity of this morphological character between the two i solates. As additional diagnostic features, the tegumentary spines are scal e-like and the region between the genital pore and the acetabulum lacks sca les. There is a folded protuberance with a pore just posterior to the genit al pore. The tegument of the acetabulum is unspined and radially wrinkled, and there are numerous randomly distributed small, domed, ciliated papillae . The sequences of the internal transcribed spacers of the nuclear rDNA com plex of the RJ and BH isolates are identical. Together these shared feature s provide strong evidence that both isolates are the same and can be referr ed to as E. paraensei. In conclusion, we have identified, for the first tim e, one of the natural definitive hosts for E. paraensei, the rodent N. squa mipes, and have extended the known geographical distribution of this specie s to include Sumidouro in Rio de Janeiro State, Brazil.