California has reported the first U.S. case of mpox (formerly monkeypox) linked to a new outbreak involving the Clade I strain. This strain differs from the Clade II strain, which has been prevalent in the U.S. since 2022. The infected individual recently traveled to Africa and is isolating at home. Clade I cases historically caused more severe illness, but recent infections appear to be less severe.
Mpox, caused by a virus related to smallpox, primarily affects remote areas of West and Central Africa and spreads through human-to-human transmission. Symptoms include fever, headaches, muscle pain, and a rash that can be painful or itchy. While the illness usually resolves within 14 to 21 days, it can be fatal for vulnerable populations. Recent outbreaks in Central and East Africa, particularly in the Democratic Republic of Congo, have caused hundreds of deaths. Vaccines can help control outbreaks but are limited to high-risk individuals or close contacts.