California health officials have confirmed the first case of clade I mpox in the United States, marking a new development in the ongoing global response to the virus. The case, identified in an individual who recently traveled from Eastern Africa, is related to an outbreak of clade I mpox currently affecting countries in Central and Eastern Africa. While the risk to the general public remains low, the confirmation prompts renewed attention to mpox prevention and surveillance, particularly as it represents a different genetic branch of the virus than the clade II variant that caused a widespread outbreak in 2022.
The California Department of Public Health confirmed the case through laboratory testing. The individual, who has not been publicly identified, sought medical care shortly after returning to the U.S. And was subsequently released after treatment. They are currently isolating at home and experiencing improving symptoms, according to state officials. Specimens from the patient have been sent to the Centers for Disease Control and Prevention (CDC) for further analysis and characterization of the virus.
This identification of clade I mpox in the U.S. Is significant since it represents a distinct strain from the clade IIb variant that drove the 2022 global outbreak. While both clades cause mpox, historically, clade I has been associated with more severe illness and higher fatality rates. However, recent outbreaks of clade I in Africa have shown lower mortality rates—around 1%—when patients receive appropriate medical care, a trend that offers some reassurance. The CDC is working with California health authorities to identify and monitor potential contacts of the confirmed case.
Understanding the Two Main Clades of Mpox
Mpox, formerly known as monkeypox, is caused by a virus that exists in two main clades: clade I and clade II. Each clade has further subdivisions. The 2022 global outbreak was primarily driven by clade IIb, which spread rapidly through close contact networks. Clade I, while historically more severe, has been primarily confined to Central and Eastern Africa. The CDC emphasizes that it is not possible to distinguish between the clades based on symptoms alone. Both can present with a characteristic rash, often on the hands, feet, chest, face, mouth, and/or genitals, and an incubation period of 3-17 days before symptoms appear.
The emergence of clade I mpox outside of Africa, with travel-associated cases reported in countries like Germany, India, Kenya, Sweden, Thailand, Zimbabwe, and the United Kingdom, has prompted increased vigilance. While these cases have generally been mild and haven’t resulted in widespread transmission, they highlight the potential for the virus to spread through international travel. The CDC has issued guidance for travelers to countries in Central and Eastern Africa experiencing outbreaks.
What the CDC is Doing to Monitor and Respond
The CDC is taking a multi-pronged approach to address the confirmed case and prevent further spread. In addition to working with California officials on contact tracing and viral characterization, the agency is leveraging its experience from the 2022 outbreak to adapt existing public health infrastructure. This includes encouraging clinicians to request expedited clade-specific testing for suspected cases with a travel history to Central and Eastern Africa. The CDC is likewise monitoring for the presence of both clades of the mpox virus in wastewater samples, providing an early warning system for potential community spread.
the CDC continues to provide support to countries in Central and Eastern Africa to control mpox transmission at its source. This support encompasses laboratory training, diagnostic testing supplies, training for healthcare workers, surveillance programs, infection control measures, and risk communication efforts. The agency has also conducted simulations to model potential clade I mpox outbreaks in the U.S., indicating that close-contact transmission within households is unlikely to lead to large-scale outbreaks, given current public health measures.
Protecting Yourself and Others
Public health officials emphasize that the risk to the general public remains low, but preventative measures are still important. The CDC recommends the following to protect against mpox:
- Avoiding close contact with anyone exhibiting symptoms of mpox, including skin lesions or genital sores.
- Avoiding contact with items that may have been contaminated by a person with mpox, such as clothing, bedding, or personal items.
- If eligible, receiving both recommended doses of the mpox vaccine.
The JYNNEOS vaccine is approved for the prevention of mpox and is available to individuals at higher risk of exposure. Vaccination remains a key strategy in mitigating the spread of the virus.
Looking Ahead: Continued Surveillance and Research
The confirmation of this first clade I mpox case in the U.S. Underscores the importance of ongoing surveillance and research. The CDC will continue to monitor the situation closely, analyze viral samples, and collaborate with state and local health departments to ensure a rapid and effective response. The agency is also committed to supporting international efforts to control mpox in Central and Eastern Africa, recognizing that containing the outbreak at its source is crucial to preventing further global spread.
The CDC anticipates releasing further updates as more information becomes available. Individuals with concerns about mpox are encouraged to consult with their healthcare provider and refer to the CDC’s mpox website for the latest guidance and information.
Disclaimer: This article provides information for general knowledge and informational purposes only, and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
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