Severe Mpox Virus Strain Possibly Spreading in LA County, Officials Warn

The virus, also called monkeypox, was discovered in several people in Los Angeles County in recent days.

An undated colorized transmission electron micrograph of mpox virus particles (pink) found within an infected cell (yellow), cultured in the laboratory, captured at the National Institute of Allergy and Infectious Diseases Integrated Research Facility in Fort Detrick, Md. NIAID/Handout via Reuters

Health officials have said that three cases of a rare strain of mpox, or monkeypox, have been confirmed in California and that they are investigating whether the virus is spreading locally.

The Los Angeles County Department of Public Health said in a statement on Oct. 17 that it is “investigating the possibility of a local spread of Clade I mpox cases after confirming its second case in an adult with no recent travel to regions where this virus is typically found,” noting that the person had been hospitalized and is now at home and recovering.

Los Angeles County Health Officer Dr. Muntu Davis said in a statement that officials have “concerns about possible local spread in Los Angeles County” after the three cases were confirmed.

“We’re working closely with our partners to identify potential sources and understand how this potentially more serious type of the mpox virus may be spreading,” Davis said.

The cases of Clade I mpox confirmed in Los Angeles County are the first in the United States to be diagnosed without any known previous travel exposure. The strain, which is considered more deadly, has been spreading in the Democratic Republic of the Congo and other African countries over the past few years.

Three days before the statement from Los Angeles County, the City of Long Beach said in a statement that it had confirmed one case of Clade I mpox in a Long Beach resident who had no previous travel history. Long Beach is located in Los Angeles County but has its own health agency.

“While the overall risk of mpox clade I exposure to the public remains low, we are taking this very seriously and ensuring our community and health care partners remain vigilant so we can prevent any more cases,” Long Beach Mayor Rex Richardson said in the statement. “This underscores the importance of continued surveillance, early response, and vaccination.”

The risk to the public is low, officials said.

The first Clade I detection was also in California, occurring in November 2024, according to the state health department.

Mpox is a rare disease caused by infection with a virus that is in the same family as the one that causes smallpox. It is endemic in parts of Africa.

Milder symptoms can include fever, chills, and body aches. In more serious cases, people can develop lesions on the face, hands, chest, and genitals.

One version of the virus, called Clade II, was the source of an international health crisis in 2022 as infections escalated in dozens of countries, mostly among males who have sex with other males. At one point, the United States was averaging close to 500 cases per day.

Long Beach health officials noted that Clade I may be more severe than the other variant and that vaccines for mpox are available.

The California Department of Public Health issued a warning on Oct. 17 that the disease may be spreading in the state and is “primarily impacting communities of gay and bisexual men.”

“As we continue to monitor the situation, it is crucial for Californians to stay informed and take preventive measures, especially persons who are more likely to be exposed to mpox,” Assistant State Public Health Officer Rita Nguyen said in a statement.

“Clade I mpox cases can be severe. Risk of severe disease and hospitalization are highest for people with weakened immune systems, so it’s critical to protect yourself by getting both doses of the mpox vaccine if you or your sex partner(s) may be at risk for mpox.”

The Associated Press contributed to this report.