Unveiling Dirofilaria asiatica sp. nov.: First Clinical Insights and Treatment Challenges for this Feline Zoonotic Filarioid Infection—A Cautionary Tale

Background: Dirofilaria asiatica sp. nov. (syn. Dirofilaria sp. Hong Kong genotype) is an emerging zoonotic filarioid nematode, initially described in human subcutaneous nodules in Hong Kong and later demonstrated in dogs and cats. This report includes the first description of clinical signs, diagnostic findings, including comparative clinicopathology, treatment and associated clinical complications in a feline infection. Methods: An 18-month-old, spayed female Domestic Shorthair cat presented with subcutaneous nodules and microfilariae in blood smears. Diagnostic work-up included PCR, a quantitative modified Knott’s test, haematology, echocardiography, and abdominal ultrasonography. Results: PCR confirmed the presence of Dirofilaria asiatica sp. nov. Haematology revealed neutrophilia (11.35 × 10³/µL) with left shift, and hyperproteinaemia (80 g/L). A quantitative modified Knott’s test revealed a microfilaremia of 36,907 per ml. Treatment with oral doxycycline and topical moxidectin triggered an acute onset of respiratory distress, managed with oxygen and dexamethasone. Nodules regressed, and microfilariae cleared by day 70. Conclusions: This case supports that indoor feline pets are susceptible to infection with Dirofilaria asiatica sp. nov. In addition, we describe for the first time, the clinical and clinicopathological findings associated with infection and highlight the risks of immunologic reactions to microfilaricidal therapy. Moxidectin and doxycycline were critical for resolution, but pre-treatment with corticosteroids is recommended. Exorbitant microfilaremia might be a critical feature in cats. The zoonotic potential of this parasite warrants heightened surveillance in endemic regions.