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%) were
microfilaremic: 8.61% from Rio de Janeiro, 21.76% from Niteroi and
its surroundings, 33.33% from the eastern shore and 30.43% 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%) were microfilaremic and 44
(7.98%) of the amicrofilaremic samples were positive for heartworm antigen
(occult infections). In Rio de Janeiro, 13.68% of the dogs were infected
(i.e., antigen-and/or microfilaria-positive) and 8.51% of the dogs had
microfilaremic infections. In comparison, Niteroi and its surroundings
showed values of 24.46% and 17.30% and the eastern shore showed values of
52.46% and 31.15%. In contrast the mountain resorts showed 20%
microfilaremic only.
