ABSTRACT
Angistrongylus costaricencis is a parasitic nematode of rodents and molluscs are the intermediate hosts. Nocturnal collection of molluscs and search for infective third stage larvae of A.costaricensis was carried out in 18 endemic foci identified by the notification of a confirmed diagnosis in human biopsies or surgical specimens. Molluscs were digested in acidic solution and isolation of larvae eventually present was done in a Baermann funnel. Larvae identified by the presence of a delicate groove in the tail were counted to asses the individual parasitic burden. Four species were found infected, with ranges of prevalence in parenthesis: Phyllocaulis variegatus (7 per cent to 33.3 per cent); Brasybaena similaris (11.7 per cent to 24.1 per cent); Belocaulus angustipes (8.3 per cent) and Phyllocaulis soleiformis (3.3 per cent to 14.2 per cent). Parasitic burden varied from 1 to 75 with P.variegatus, 1 to 98 with B. similaris, 1 to 13 with B.angustipes and 1 larvae in each of two specimens of P.soleiformis. P.variegatus was present in all sites and was found infected with the highest prevalence figures and the highest individual parasitic burdens. These data strss the importance of veronicellid slugs as intermediate hosts for A.costaricensis in the endemic areas in Rio Grande do Sul, Brazil.