RESUMEN
In order to evaluate the prevalence of canine heartworm in the State of Rio de Janeiro, a multicenter survey was carried out in two phases. The survey involved 1376 dogs from two cities: Rio de Janeiro and Niteroi, and its surroundings, including the eastern shore and mountain resorts, which were further divided into sections. In the first phase, 795 dog blood samples were examined by the modified Knott test for the detection of microfilariae. A total of 134 samples (16.85 per cent) were microfilaremic: 8.61 per cent from Rio de Janeiro, 21.76 per cent from Niteroi and its surroundings, 33.33 per cent from the eastern shore and 30.43 per cent from the mountain resorts. In the second phase, 595 dog blood samples were examined first by the modified Knott test and the amicrofilaremic samples were subsequently examined by an immunoenzymatic test (ELISA) for antigen detection. In summary, 83 samples (13.95 per cent) were microfilaremic and 44 (7.98 per cent) of the amicrofilaremic samples were positive for heartworm antigen (occult infections). In Rio de Janeiro, 13.68 per cent of the dogs were infected (i.e. antigen-and/or microfilaria-positive) and 8.51 per cent of the dogs had microfilaremic infections. In comparison, Niteroi and its surroundings showed values of 24.46 per cent and 17.30 per cent and the eastern shore showed values of 52.46 per cent and 31.15 per cent. In contrast the mountain resorts showed 20 per cent microfilaremic only.