California has confirmed the first U.S. case of mpox from the Clade I strain, linked to a new outbreak. This differs from the Clade II strain that has circulated in the U.S. since 2022.
The individual, now isolating at home, had recently traveled to Africa. According to California’s Department of Public Health (CDPH), the case is connected to the ongoing Clade I mpox outbreak in Central and Eastern Africa.
Mpox, previously known as monkeypox, was declared a global health emergency by the World Health Organization earlier this year. While Clade I cases historically caused more severe illness than Clade II, recent infections appear to be less clinically severe.
Caused by a virus related to smallpox, mpox is generally less dangerous. Initially transmitted from animals to humans, it now spreads between humans. Symptoms include fever, headaches, swollen lymph nodes, muscle aches, and a painful or itchy rash. The illness typically resolves within 14 to 21 days but can be fatal, especially for vulnerable groups like small children.
Mpox is most common in remote areas of West and Central Africa, particularly in the Democratic Republic of Congo (DR Congo), where it has been observed for years. Earlier this year, hundreds died during an outbreak in DR Congo, with the disease spreading further into Central and East Africa.
