California has recorded the first US case of mpox – formerly known as monkeypox – part of a new outbreak.

The state health department, CDPH, said the new case is a clade I strain — which is different from the clade II strain that has been circulating in the US since 2022.

The person in question, who is now isolated at home, had recently traveled to Africa and the CDPH said his case was “related to the ongoing outbreak of clade I MPox in central and eastern Africa”.

had mpox Global health emergency declared by the World Health Organization earlier this year.

The CDPH stated that while clade I cases had caused more severe disease than clade II in the past, “recent infections with clade I MPox may not be as clinically severe as previous outbreaks”.

Mpox is caused by a virus in the same family as smallpox but is usually much less harmful.

It originally spread from animals to humans but now also spreads among humans.

Initial symptoms include fever, headache, swelling, back pain, and muscle pain. A rash may then develop, which may be extremely itchy or painful.

The infection may clear up on its own and last between 14 and 21 days, but in some cases it is fatal, especially for vulnerable groups including young children.

Mpox is most common in remote villages in the tropical rainforests of West and Central Africa, in countries such as the Democratic Republic of the Congo (DR Congo), where it has been observed for many years.

Hundreds of people died during the initial outbreak in DR Congo earlier this year, and the disease has since spread across regions of central and eastern Africa.

Outbreaks can be controlled by preventing infection with vaccines, although these are usually only available to at-risk people or those who have been in close contact with an infected person.