Two asymptomatic Dirofilaria asiatica infections identified in Sri Lanka

The two cases were detected in night blood smears during lymphatic filariasis surveillance in Kalutara district, Sri Lanka. A 60-year-old man had 7 microfilariae per 60 μL of blood; a 14-year-old boy had 3 per 60 μL. Both were otherwise largely asymptomatic. The older patient had longstanding bilateral leg swelling, while the younger patient had mild eosinophilia and an occasional dry cough. Imaging and other examinations were unremarkable.

Microscopy suggested Dirofilaria, and sequencing of the mitochondrial COI gene identified D. asiatica in both patients, with more than 99% identity to reference sequences. The adult received diethylcarbamazine and albendazole, with microfilaremia cleared at five weeks. The boy received doxycycline and albendazole; microfilaremia persisted at one month, prompting repeat treatment, and was cleared by three months.

These cases document human D. asiatica microfilaremia in Sri Lanka, where the species has also been reported in dogs. The authors note that human Dirofilaria infections are usually amicrofilaremic and that several treatment regimens have been used without an established preference. The findings are limited to two cases and do not establish comparative treatment effectiveness. The article is an early release and is not yet the final version.