Dirofilaria asiatica sp. nov. (Spirurida: Onchocercidae) - Defined using a combined morphological-molecular approach.

Parasitic nematodes of the family Onchocercidae (superfamily Filarioidea) have evolved alongside vertebrate hosts for millions of years. While morphological methods have played a central role in identifying species, many taxa remain cryptic and are challenging to differentiate, complicating diagnosis and the understanding of their epidemiology. Among the clinically relevant genera are Onchocerca and Dirofilaria, the latter being responsible for illnesses such as heartworm disease in canines and rare zoonotic infections in humans. Despite advances in our knowledge of the canine heartworm (Dirofilaria immitis), substantial gaps remain regarding other Dirofilaria spp. and genotypes, and their impact on both animal and human health. In this study, we conducted the first known comprehensive morphological and molecular characterisation of a novel Dirofilaria sp., Dirofilaria asiatica sp. nov., from Canis lupus familiaris in Sri Lanka. This new species, genetically consistent with a previously identified novel genotype of Dirofilaria, initially found in humans in Hong Kong, was described using a combined morphological and molecular approach. The findings reveal that D. asiatica sp. nov. differs significantly from other known species, including D. repens and D. immitis, and might be responsible for the majority of zoonotic Dirofilaria infections in southern and southeastern Asia. Furthermore, the identification of cryptic Dirofilaria spp. in both canine and human hosts emphasises the importance of molecular tools for specific identification, particularly when morphological information is inadequate. This study provides insights into the taxonomy and zoonotic potential of D. asiatica sp. nov., as well as its relationship with related species of onchocercids. This combined morphological and molecular approach establishes a framework for future investigations of filarioid nematodes, with implications for improving diagnosis and understanding of their epidemiology in both veterinary and medical contexts.