California health officials have confirmed the first U.S. case of the more virulent "clade Ib" mpox strain in an individual who recently traveled from Africa. The case is linked to the ongoing outbreak in Central and Eastern Africa that has already caused tens of thousands of infections and over a thousand deaths.
"The affected individual received health care in San Mateo County, based on their travel history and symptoms," California health officials stated in an alert issued Saturday. "The individual is isolating at home and recovering. People who had close contact with this individual are being contacted by public health workers."
Officials emphasized there is currently no evidence that this form of mpox is spreading between individuals in California or elsewhere in the United States.
Global Spread of Clade Ib Mpox
The California case adds to a growing list of travel-related clade Ib mpox cases reported outside Africa. Similar cases have been identified in Germany, India, Kenya, Sweden, Thailand, Zimbabwe, and the United Kingdom. Most notably, the UK recently reported its first cluster of four cases, with three infections occurring in people who shared a household with the initial case.
"Mpox is very infectious in households with close contact, and so it is not unexpected to see further cases within the same household," noted Susan Hopkins, chief medical adviser at the UK Health Security Agency.
Understanding the Severity of Clade I Mpox
The U.S. Centers for Disease Control and Prevention (CDC) has provided context on the severity of this strain compared to the clade II variant that caused a global outbreak in 2022.
"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 stated in its alert.
While previous outbreaks of clade I mpox have typically had death rates between 3% and 11%, more recent outbreaks have shown death rates as low as approximately 1% with good medical care. The CDC emphasized that "death rates are expected to be much lower in countries with stronger healthcare systems and treatment options, including the United States."
The African Outbreak Situation
The Democratic Republic of Congo (DRC) remains the epicenter of the current outbreak. Since January, the DRC has reported more than 47,000 suspected clade I mpox cases and over 1,000 suspected deaths, according to CDC data. The virus has spread to neighboring countries, including Burundi, Central African Republic, Republic of the Congo, Rwanda, and Uganda.
In response to the crisis, the World Health Organization (WHO) recently allocated nearly 900,000 vaccine doses to the nine African countries hardest hit by the mpox surge. However, health experts warn this falls far short of the estimated 3 million vaccines needed in the DRC alone, with another 7 million required for the rest of the continent.
"If we miss this opportunity, the likelihood of another significant outbreak increases substantially," warned Dr. Zakary Rhissa, who heads operations in Congo for the charity Alima.
Recognizing Mpox Symptoms and Prevention
Mpox, formerly known as monkeypox, is a viral disease related to smallpox. It spreads through close contact such as touching, kissing or sex, as well as through contaminated materials like sheets, clothing and needles.
Initial symptoms resemble influenza, including fever, chills, exhaustion, headache, and muscle weakness. These are followed by a painful or itchy rash with raised lesions that eventually scab over and resolve within weeks.
The CDC advises avoiding contact with symptomatic individuals and potentially contaminated materials. People who are eligible should receive two doses of the mpox vaccine for protection.
Healthcare System Preparedness
Health authorities are monitoring the situation closely while emphasizing that the risk to the general public remains low. The National Health Service (NHS) in the UK has stated they have plans in place to expand vaccine rollout quickly if needed.
As the situation evolves, public health agencies continue to enhance surveillance and preparedness measures to prevent further spread of this more virulent mpox strain.
