Evaluation of an enzyme-linked immunosorbent assay for occult dirofilariasis in a population of naturally exposed dogs.

Dogs seen at a veterinary teaching hospital were classified on the basis of their apparent exposure to filarial worms, and their sera were examined in an enzyme-linked immunosorbent assay test, using a Dirofilaria immitis-derived antigen. The geometric mean titers of 103 dogs varied from 30 (61 noninfected dogs) to 2,896 (in 8 dogs without microfilaremia, but with signs of occult dirofilariasis [respiratory insufficiency, radiographic evidence of pulmonary hypertension] and a history of possible exposure to the mosquito vectors of heartworms). The mean titer of 28 dogs with patent filarial infections was 122, slightly higher than the mean titer of 64 in 8 dogs with a history of previous heartworm infection. The titers of dogs with evidence suggestive of occult dirofilariasis were significantly higher (P = 0.05) than the mean titers of those without evidence of filarial infections, with patent filarial infections, or with a history of dirofilariasis.