Description
Dirofilaria immitis (heartworm) in dogs causes cardiopulmonary disease with coughing, exercise intolerance, dyspnoea, weight loss, and right heart failure (ascites, syncope) in heavy infections; caval syndrome (haemoglobinuria, collapse) occurs with high worm burdens in pulmonary arteries/heart. In cats, as atypical hosts, it leads to heartworm-associated respiratory disease (HARD) with acute coughing, dyspnoea, vomiting, lethargy, or sudden death from pulmonary thromboembolism after immature worm death.
Dirofilaria repens primarily causes subcutaneous nodules or dermatitis in dogs (often asymptomatic carriers), rarely ocular migration; cats may show similar mild skin lesions.
Acanthocheilonema reconditum (Dipetalonema reconditum) is generally non-pathogenic in dogs, causing incidental microfilaria detection without clinical signs.
Samples for diagnosis include EDTA blood for antigen testing (detects female D. immitis antigens, highly sensitive in dogs >6 months post-infection), modified Knott’s test or microfilaria filtration for speciation (distinguishes D. immitis from D. repens/A. reconditum), and echocardiography/radiographs for worms. In cats, antibody testing supplements antigen (often negative due to low burden).
Quantitative PCR (qPCR) on blood excels for detecting/quantifying all species DNA, speciating microfilariae (D. immitis, D. repens, A. reconditum), confirming occult infections, and monitoring therapy.
Wolbachia spp. are obligate intracellular endosymbionts of filarial nematodes, contributing to pathology via inflammation; standalone infection does not occur. qPCR detects Wolbachia DNA in blood/tissue alongside filarial DNA, assessing treatment response (reduced loads post-doxycycline), though not routinely used for primary diagnosis.
