Canine Dirofilaria immitis Infection in a Tropical Area Recently Colonized by the parasite

In Brazil, the nematode Dirofilaria immitis is endemic throughout the coastal region, but the distribution pattern has changed in recent years in places previously without occurrence or with low prevalence. The Baixada Fluminense in the state of Rio de Janeiro, Brazil, once considered a region free of canine heartworm disease, has raised growing concerns about the etiological profile of D. immitis . The region, known for its ecological diversity, has favorable conditions for the maintenance and spread of the nematode, providing important insights into the endemicity of the disease in relation to the socio-environmental determinants of the area. The aim was to evaluate the risk factors related to the circulation of dogs susceptible to Dirofilaria immitis infection that influence prevalence in the municipalities of Duque de Caxias and Magé, Baixada Fluminense, RJ. Between 2022 and 2024, active search was carried out on dogs living near environmental conservation areas. A total of 260 blood samples were collected and sent for serological, parasitological and molecular analysis. The seroprevalence of filarioids in dogs was 20% (52/260), confirming the species D. immitis and Acanthocheilonema reconditum by molecular analysis (42.3%; 22/52). Only 9 microfilaremic samples were antigen negative, therefore 23.5% (61/260) of the dogs were infected by D. immitis . Health education ef-forts should be undertaken to increase awareness of canine heartworm disease among professionals and pet owners.