Severe form of Mpox (Clade Ⅰb) confirmed for the first time in Japan - Woman in her 20s with travel history to Africa / Announcement by the Ministry of Health, Labour and Welfare

On September 16, 2025, the Ministry of Health, Labour and Welfare and the city of Kobe announced the first confirmed case in Japan of a high-risk Mpox (formerly "monkeypox") virus infection known as Clade I, specifically "Clade Ib." The infection was identified in a woman in her 20s with a travel history to Africa. After returning to Japan, she developed symptoms such as fever, rash, blisters, and swollen lymph nodes, and sought medical attention on September 12. A viral strain test conducted at a research institute in Kobe identified it as "Clade Ib." This strain is endemic to regions like Central Africa and is associated with a relatively high rate of severe cases and mortality in past outbreaks. Until now, all cases detected in Japan belonged to the milder "Clade II" lineage. The patient's condition is stable, and investigations have not confirmed any clear chain of community transmission within Japan. However, the Ministry of Health, Labour and Welfare is monitoring the outbreak situation both domestically and internationally, strengthening infection surveillance and medical systems, and issuing public advisories. Mpox has an incubation period of 7-14 days (up to 5-21 days) and often resolves naturally within 2-4 weeks after onset. However, there is a higher risk of severe illness in children, immunocompromised individuals, and pregnant women, making early diagnosis, isolation, and preventive measures crucial.