Biological aspects of a new isolate of Echinostoma paraensei (Trematoda: Echinostomatidae): susceptibility of sympatric snails and the natural vertebrate host.

A new isolate of Echinostoma paraensei (Lie & Basch, 1967) was obtained from a natural vertebrate host, the water rat Nectomys squamipes. Relationships with sympatric snails, Biomphalaria glabrata; Physa marmorata and Lymnaea columella, as well as allopatric snails and the definitive hosts N. squamipes, Mus musculus, Rattus norvegicus, Mesocricetus auratus and birds were investigated. E. paraensei developed in all sympatric snail species following exposure to one or five miracidia. P. marmorata showed the highest infection rate (34% and 36%) followed by L. columella (18% and 24%) and B. glabrata (8% and 28%), respectively. Mortality was elevated in the patent period, with L. columella having the highest values. B. glabrata, P. marmorata, and L. columella did not differ in relation to cercarial encystment, and metacercariae from each species were able to infect N. squamipes with similar worm burdens. Recovered adult worms were found in clusters from the first to third sections of the small intestine. Miracidia of E. paraensei hatched after 10 days incubation in darkness in dechlorinated water at 28+/-1 micro C. Miracidia began to hatch 1 h after exposure to incandescent light.