United States' first known case of more severe strain of mpox is confirmed in Northern California

Health officials said Saturday they have confirmed the first U.S. case of a new form of mpox that was first seen in eastern Congo.

The person had traveled to eastern Africa and was treated in Northern California upon return, according to the California Department of Public Health. Symptoms are improving and the risk to the public is low.

The individual was isolating at home and health workers are reaching out to close contacts as a precaution, the state health department said.

Mpox is a rare disease caused by infection with a virus that's in the same family as the one that causes smallpox. It is endemic in parts of Africa, where people have been infected through bites from rodents or small animals. Milder symptoms can include fever, chills and body aches. In more serious cases, people can develop lesions on the face, hands, chest and genitals.

Earlier this year, scientists reported the emergence of a new form of mpox in Africa that was spread through close contact including through sex. It was widely transmitted in eastern and central Africa. But in cases that were identified in travelers outside of the continent, spread has been very limited, according to the U.S. Centers for Disease Control and Prevention.

More than 3,100 confirmed cases have been reported just since late September, according to the World Health Organization. The vast majority of them have been in three African countries - Burundi, Uganda, and the Democratic Republic of the Congo.

Since then, cases of travelers with the new mpox form have been reported in Germany, India, Kenya, Sweden, Thailand, Zimbabwe, and the United Kingdom.

Health officials earlier this month said the situation in Congo appears to be stabilizing. The Africa CDC has estimated Congo needs at least 3 million mpox vaccines to stop the spread, and another 7 million vaccines for the rest of Africa. The spread is mostly through sexual transmission as well as through close contact among children, pregnant women and other vulnerable groups.

The current outbreak is different from the 2022 global outbreak of mpox where gay and bisexual men made up the vast majority of cases.