First human infection with Onchocerca takaokai (Spirurida: Onchocercidae) presenting as creeping eruption in Japan

Zoonotic onchocerciasis is a rare human infection caused by Onchocerca species that normally parasitize non-human mammals. In Japan, all previously reported human cases have been attributed to Onchocerca japonica and have presented as localized, non-migratory subcutaneous nodules. Here, we report the first human infection caused by Onchocerca takaokai Uni et al., 2015. A 24-year-old male presented with linear migratory erythema on the forearm, clinically consistent with creeping eruption. Histopathological examination revealed an adult female filarial nematode with polymyarian-coelomyarian musculature, without internal cuticular ridges in the lateral cords, and lacking transverse ridges on the cuticle. Molecular analyses of the mitochondrial 12S rRNA and cytochrome c oxidase subunit I (cox1) genes confirmed that the parasite was O. takaokai, a parasite of wild boars in Japan. This case demonstrates a clinical presentation distinct from that of O. japonica and suggests that O. takaokai should be considered in the differential diagnosis of creeping eruption in endemic areas.