First molecular characterization of Dirofilaria vector species and the distribution of canine dirofilariasis in Gampaha district, Sri Lanka.

Dirofilariasis is a vector-borne parasitic infection caused by filarial nematodes belonging to the genus Dirofilaria. Sri Lanka has reported the highest prevalence of human dirofilariasis cases in Asia. Molecular-based detection of Dirofilaria vector species has not yet been conducted in Sri Lanka, which could provide more sensitive information by directly detecting and analyzing genetic material. The present study aimed to analyze the distribution of canine dirofilariasis and to determine the Dirofilaria vector species in Gampaha district, Sri Lanka, using molecular-based techniques. Mosquito sampling (n=300) was performed from October to December 2024 from different sites in Gampaha district. The gut of the mosquitoes was dissected. Genomic DNA extraction followed by PCR was performed with specific primers for Dirofilaria species. The blood samples of different dog breeds (n=500) were also collected from the Gampaha district, and they were subjected to DNA extraction, PCR amplification, and sequencing. The data were analyzed by bioinformatics tools. Analysis of the sequence data confirmed the first molecular detection of the dirofilariasis vector in Sri Lanka; Armigeres subalbatus as the potential vector mosquito for Dirofilaria repens and Dirofilaria asiatica n. sp. The sequence of D. repens recorded from Sri Lanka is not available in the literature/or any database, and the sequence of D. repens was also determined. Further, in different dog breeds, the infection rate of microfilariae was found to be different, and the Rottweiler breed was recorded with the highest infection rate. D. repens and D. asiatica n. sp. were found in dog blood samples. The phylogenetic analysis revealed that the query sequence of the D.repens parasites isolated from the present study showed considerable homology and proximity to the D. repens recorded from India. Armigeres subalbatus is the vector mosquito for D.repens and D.asiatica n. sp., which caused canine dirofilariasis in the Gampaha district of Sri Lanka. No other mosquito species were identified as potential vectors of Dirofilaria species in the study area. This is, to our knowledge, the first D. repens sequence found in the Gampaha district, Sri Lanka. The present study findings provide very important insights for targeted vector control programs for Dirofilaria parasites in Sri Lanka.