Zoonotic infection caused by Onchocerca japonica (Nematoda: Filarioidea) in a 69-year-old woman in Kanto Region, Eastern Honshu, Japan

Reports of zoonotic infections caused by the filarial nematode Onchocerca japonica have recently increased in Japan. A 69-year-old woman living in Sosa City, Chiba Prefecture, Kanto Region, Honshu, developed a painful nodule at the metacarpophalangeal joint of the index finger of her right hand. The causative agent was identified as a female O. japonica based on the histopathological characteristics (i.e., cuticle with transverse triangular ridges but without inner striae) of the biopsy specimens of the nodule. The species identification was corrobo-rated by cox1 gene sequencing of the worm tissues isolated from paraffin-embedded sections of the specimens. Subsequent to the excision of the nodule, followed by anthelmintic treatment, the patient remained asymp-tomatic. Human infection with O. japonica has not previously been reported in Kanto Region, Eastern Honshu. The present case is likely linked to the recent expansion of the geographic range of the Japanese wild boar into this area.

Automated summary

Reports of zoonotic infections caused by the filarial nematode Onchocerca japonica have increased in Japan recently. This case report describes a 69-year-old woman in Sosa City, Chiba Prefecture, who developed a painful nodule on the finger joint. The causative agent was identified as female O. japonica based on histopathological characteristics and gene sequencing. The case is likely linked to the geographic range expansion of Japanese wild boar.