Human otoacariasis by Amblyomma testudinarium identified with 16S rRNA gene sequencing

Human otoacariasis caused by tick bites in the external auditory canal is rarely reported in Japan, despite the recent increase in the movement of wild animals, known hosts of ticks into human living areas due to global warming. We report a case of human otoacariasis caused by Amblyomma testudinarium, genetically identified using 16S rRNA gene sequencing. A 43-year-old man presented to an urban hospital in Tokyo with left-sided otalgia. An endoscopic examination revealed a tick anchored to the skin of the external auditory canal, which showed erythema and swelling. Initial attempts to remove the tick were unsuccessful because it was firmly attached by a cement-like substance. Thereafter, the patient was treated with antibiotic and corticosteroid ear drops, which resulted in tick death and a reduction in inflammation. The shrunken tick was then successfully removed, and polymerase chain reaction analysis confirmed its species as Amblyomma testudinarium. Although a stereomicroscopic examination revealed a small defect in the tick mouthparts, no symptoms were observed during a follow-up period of more than one month. This case highlights the clinical importance of accurate tick species identification, even in urban environment, due to the potential risk of tick-borne diseases such as severe fever with thrombocytopenia syndrome.