MONDAY, Nov. 18, 2024 (HealthDay News) -- As Africa continues to battle an outbreak of the newer "clade Ib" strain of mpox, California officials have confirmed the first known U.S. case of this strain of the virus.

The subtype of clade I mpox virus has already caused widespread misery in Congo and other African nations.

"This case was confirmed in an individual who recently traveled from Africa and is related to the ongoing outbreak of clade I mpox in Central and Eastern Africa," state officials said in a health alert issued Saturday.

"The affected individual received health care in San Mateo County, based on their travel history and symptoms.," the alert says. "The individual is isolating at home and recovering. People who had close contact with this individual are being contacted by public health workers, but there is no concern or evidence that [this form of] mpox clade I is currently spreading between individuals in California or the United States."

Travel-related cases of clade Ib mpox have also been reported in Germany, India, Kenya, Sweden, Thailand, Zimbabwe and the United Kingdom, according to an alert issued Saturday by the U.S. Centers for Disease Control and Prevention.

“The recent travel-associated clade I mpox cases outside of Africa have all been attributed to subclade Ib; there have been no deaths associated with these cases and available data for a subset has detailed relatively mild disease courses,” the CDC noted in its alert.

“Historically, clade I mpox has caused more severe illness and deaths than clade II mpox; however, recent data demonstrate that infections from clade I mpox in the current outbreak may not be as clinically severe as in previous outbreaks," the CDC added.

While outbreaks of clade I mpox have typically had death rates of between 3% and 11%, more recent outbreaks have had death rates as low as approximately 1% with good medical care, the agency noted.

"Death rates are expected to be much lower in countries with stronger health care systems and treatment options, including the United States,” the CDC said.

Following an international outbreak of the less serious strain of mpox in 2022, clade II mpox has already been circulating in the United States, the CDC noted.

Meanwhile, the number of mpox cases in Africa continues to climb, driven mostly by cases in the Democratic Republic of Congo.

Since January, that country has reported more than 47,000 suspected clade 1 mpox cases and more than 1,000 suspected deaths, according to the CDC, and the virus has spread to neighboring countries, including Burundi, Central African Republic, Republic of the Congo, Rwanda and Uganda.

Mpox, formerly known as monkeypox, is a viral disease related to the now-eradicated smallpox virus. It can spread through close contact such as touching, kissing or sex, as well as through contaminated materials like sheets, clothing and needles, according to the WHO.

Initial symptoms mirror the flu -- fever, chills, exhaustion, headache and muscle weakness. After that, a painful or itchy rash with raised lesions develops, scabs over and resolves over in a matter of weeks.

To avoid infection, steer clear of with people with symptoms and contaminated materials such as clothing, bedding, sex toys and toothbrushes, the CDC advises. People who are eligible should get two doses of mpox vaccine.

More information

The CDC has more on mpox.

SOURCE: California Department of Public Health, news release, Nov. 16, 2024; U.S. Centers for Disease Control and Prevention, news release, Nov. 16, 2024