The frequency of canine heartworm disease was determined in 310 dogs (158 males and 152 females) from São Paulo city (154) and several towns along the São Paulo state coast (156). The survey was carried out through the Knott's technique (direct presence of microfilariae in the blood) and ELISA for soluble circulating antigen detection. Twenty five (8.0%) samples were positive to D. immitis using both methods being 6 dogs (3.9%) from the city and 19 (12.2%) from the coastal area. Nineteen dogs (6.1%) were positive to the Knott's technique (4 from the city and 15 from the coastal area) and 12 dogs (3.9%) to the ELISA (4 from the city and 8 from the coastal area); six dogs (1.9%) were positive for both methods being two from the city and four from the coastal area. The frequency of positive dogs by the Knott's technique in the coastal area was higher than that in São Paulo city (P<0.05), but equivalent frequency was found in dogs from both areas when the ELISA test was used. Higher number of dogs with a patent infection (microfilaremic) was found than those with occult infection (amicrofilaremic). This survey has shown that the dogs were not infected with high frequency probably because the studied areas were not hiperenzootic endemic (higher than 10% of frequency).
Dog; canine heartworm disease; Dirofilaria immitis; ELISA; frequency