First known case of rare mpox strain confirmed in United States

The California Department of Public Health (CDPH) has reported the first known U.S. case of an emerging strain of the mpox virus, according to a CDPH release Saturday.

The case of "clade I mpox" was identified in a traveler recently returned from Africa, where this strain is actively circulating. Officials with the CDPH have emphasized that the risk to the public remains "very low."

The individual, who sought medical care in San Mateo County due to their travel history to East Africa and symptoms, is in isolation at home.

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The clade I mpox, historically associated with more severe illness than clade II — the strain responsible for outbreaks in California and the U.S. since 2022 — has shown milder clinical presentations in recent cases as long as patients receive medical care.

CDPH has informed the Centers for Disease Control and Prevention (CDC) of the case, and specimens from the patient are being sent for further laboratory analysis.

The new strain of mpox was recorded in a case discovered in California, the first in the United States. (iStock)

Public health officials are contacting those who may have had close contact with the patient, though there is no evidence of community transmission of clade I mpox in California or the rest of the country.

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Both clade I and clade II mpox spread primarily through close, skin-to-skin, intimate, or sexual contact. In their release, the CDPH also reassured the public that casual contact, such as in offices, classrooms, or stores, poses minimal risk of mpox transmission.

According to the CDC, the latest strain primarily spreads through close skin-to-skin contact, including sexual contact, and has the potential to cause severe illness and even fatalities. It emerged first in the eastern Congo.

A patient infected with mpox shows lesions on his body in Kamituga, South Kivu province in the east of the Democratic Republic of Congo, Sept. 20.  (Glody Murhabazi/AFP via Getty Images)

Since September, over 31,000 confirmed cases of this strain of mpox have been documented globally, with the majority concentrated in three African countries: Burundi, Uganda, and the Democratic Republic of the Congo, as reported by the World Health Organization.

The CDC has also identified travel-related cases of this new mpox strain in countries including Germany, India, Kenya, Sweden, Thailand, Zimbabwe, and the United Kingdom.

The CDC has issued enhanced precautions for travelers to Central and Eastern Africa, where clade I mpox outbreaks are ongoing.

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No deaths have been reported yet from this new strain, according to the CDC.

The CDPH did not immediately respond to Fox News Digital's request for comment.