Heartworm disease is a health problem for dogs and cats, especially in tropical and subtropical coastal regions of the world. Some studies have compared the efficacy of the diagnostic techniques used to detect this parasitosis. Therefore, the aim of this study was to compare parasitological optical microscopy (POM), serological and molecular techniques for diagnosing canine heartworm infection. Samples were collected between July 2015 and April 2016 from 103 dogs in Cabo Frio, RJ, Brazil. The wet fresh blood, thick smears, thin smears and modified Knott’s test were used to detect microfilariae. ELISA (Snap™ 4Dx ® IDEXX) was used to detect antigens and the polymerase chain reaction (PCR) was used to detect DNA and enable sequencing for species differentiation and confirmation. 19.4% of samples were positive according to microscopy. Through PCR, 15.5% of the total were positive. Using ELISA, the positivity rate was 29.1%. Occult heartworm infection was detected in 11.6% of the samples. ELISA sensitivity was shown to be higher than PCR or microscopy (P = 0.001). Sequencing of samples confirmed the presence of Dirofilaria immitis and Acanthocheilonema reconditum . ELISA was more effective for serological diagnosis canine heartworm and should be used in clinical and epidemiological studies.

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