Subconjunctival Granuloma Caused by Dirofilaria repens in an Indoor Dog From Thailand: A Case Report and Mitochondrial Genome Analysis.

Objective: To describe a subconjunctival granuloma caused by Dirofilaria repens in a dog from Rayong province, eastern Thailand, along with the successful treatment outcomes. The causative nematode was identified through morphological examination and molecular techniques.

Animal studied: A 5-year-old female mixed-breed dog was presented with a subconjunctival mass at the temporal part of the left bulbar conjunctiva. The dog lived indoors with its owner.

Methods: A complete ophthalmic examination was performed. The mass was surgically removed and submitted for histopathological examination. During the surgery, a long, slender, white-creamy nematode emerged from the mass, which was sent for parasitology examination and molecular identification. The left eyelids were closed using temporary tarsorrhaphy. Selamectin spot-on and doxycycline were prescribed.

Results: Two weeks after surgery, the temporary tarsorrhaphy was removed. The excision site had healed completely without recurrence. The histopathological examination revealed eosinophilic granulomatous inflammation. A parasitic nematode was identified in the genus Dirofilaria spp. The full-length mitochondrial genome analysis showed 99.8% coverage of Dirofilaria repens sequences.

Conclusion: D. repens infection caused a subconjunctival granuloma in the current case. The treatments, combined with surgical excision and selamectin spot-on, resulted in a good response. The conjunctival wound had healed completely within 2 weeks, without complications or recurrences. To the authors' knowledge, this was the first report of canine subconjunctival dirofilariasis caused by D. repens in Thailand. The vector-borne transmission of D. repens, a zoonotic nematode, via mosquito bites in humans, should be a concern in Thailand, particularly in the eastern region.