Subclinical dirofilariosis in dogs in Croatia - results of retrospective research based on archived blood samples

Dirofilariosis is an emerging vector-borne disease of dogs and other canids transmitted by female mosquitoes of the Culicidae family, and caused by filarial nematodes of the genus Dirofilaria. Dirofilaria immitis mainly infects the pulmonary arteries and right heart chambers, and it can cause heartworm disease in dogs, while D. repens is found mainly in subcutaneous tissue and causes subclinical infection. Both have zoonotic potential. Human infections caused by D. repens are increasing in Europe, and it is emerging as a serious public health threat. Scientific interest has tended to focus mostly on D. immitis because of its pathogenicity and veterinary importance. This study aimed to update the information about dirofilariosis in the canine population in Croatia. Therefore, 531 blood samples were tested for the presence of microfilariae using a modified Knott's test and a commercial test for detection of D. immitis circulating antigens. Microfilaremia was detected in 8.1% of the tested dogs, of which 7.9% were caused by D. repens and 0.4% by D. immitis. A single sample (0.2%) showed a mixed infection with both D. repens and D. immitis. The seroprevalence for D. immitis was 0.4%. No occult D. immitis infection was detected, and microfilariae were detected in all antigen-positive samples.