Morpho-molecular identification of heartworms (Dirofilaria immitis) in domestic dogs in the Sucre canton, Ecuador.

Dirofilaria immitis, the etiologic agent of heartworm disease in dogs, is a mosquito-borne nematode that primarily affects the cardiopulmonary system. The objective of this study was to morphologically and molecularly characterize the nematodes found in a naturally infected dog in the Sucre canton of Ecuador. It is a tropical coastal region with favorable conditions for vector proliferation, but with limited epidemiological information. The necropsy of the infected dog revealed adult nematodes located in the right ventricle and pulmonary arteries, exhibiting the sexual dimorphism characteristic of D. immitis. Parasites were molecularly analyzed using PCR amplification of the cox1 and 18S rRNA genes, followed by Sanger sequencing and phylogenetic comparison with reference strains from the NCBI/GenBank database. All isolates showed 100 % query coverage, with identities ranging from 99 to 100 % with known D. immitis strains. Phylogenetic trees constructed using the Maximum Likelihood and Neighbor-Joining methods positioned local isolates within well-supported D. immitis clades, indicating high genetic similarity with reference strains from Asia, Europe, and South America. This integrated diagnostic approach highlights the value of combining morphological and molecular tools for accurate parasite identification. Furthermore, the study provides essential reference data for veterinary surveillance programs on the Ecuadorian coast. This information supports the implementation of early diagnosis, control, and prevention strategies, contributing to improving the health of domestic dogs and reducing the risk of zoonotic transmission in vulnerable tropical ecosystems.