A recent returnee from Africa has tested positive for a severe form of Mpox, sparking health alerts in California. This marks the first known U.S. case of this specific strain, known as Clade Ib, which has been responsible for a deadly outbreak across parts of Africa.
The patient, who remains unidentified, arrived from East Africa and has been diagnosed in San Mateo County, near San Francisco. Health officials from both the California Department of Public Health and the Centers for Disease Control and Prevention (CDC) have immediately stepped in, reaching out to those who may have come into contact with the patient. As of now, the individual is in isolation at home, taking necessary precautions to prevent potential spread.
The Mpox strain in question, Clade Ib, has been linked to a significant outbreak in Central and Eastern Africa, where it has caused substantial health concerns. According to the CDC, there is currently no indication that Clade Ib is spreading within U.S. communities. This case, however, highlights the ongoing risk posed by international travel, especially to regions where the virus is prevalent.
Although Mpox cases have been identified among travelers in various countries—such as Germany, Sweden, Thailand, and the United Kingdom—local outbreaks have generally been contained. For instance, transmission in Germany, Sweden, and Thailand did not extend beyond the initial patients. However, in the United Kingdom, an infected individual did pass the virus to three family members, underscoring the virus’s ability to spread through close contact.
Mpox, previously known as monkeypox, is classified into two main variants: Clade I and Clade II. Clade I, which includes the Clade Ib subtype now seen in the U.S., has primarily affected parts of Africa, leading to a significant number of cases and deaths. This version of the virus is distinct from Clade II, which caused a global outbreak in 2022. The Clade II epidemic primarily impacted gay and bisexual men, spreading rapidly across 116 countries and infecting almost 100,000 individuals.
In contrast, Clade I’s impact has been more concentrated, with the current outbreak causing over 57,000 cases and nearly 1,200 deaths in 2024 alone. Many of the fatalities have involved children, raising alarm among global health organizations. Due to the severity of this strain, the World Health Organization (WHO) declared the situation a global health emergency.
Clade Ib, the subtype currently in focus, was traditionally associated with infections resulting from consuming contaminated meat or having direct contact with infected animals or individuals. However, recent findings have revealed a shift in transmission patterns. In 2023, experts observed that the virus had begun spreading sexually, often linked to heterosexual prostitution networks. This shift has raised concerns about the evolving nature of Mpox transmission and the implications for public health.
While the CDC emphasizes that the general risk to the American public remains low, this case underscores the importance of vigilance, particularly for travelers returning from affected regions. The agency has noted that even with the detection of Clade Ib in the U.S., there are no signs of widespread community transmission. Authorities continue to monitor the situation, urging anyone with potential exposure to seek testing.
Mpox is primarily transmitted through direct and prolonged contact with an infected person. This often includes exposure to bodily fluids, lesions, or respiratory droplets. The incubation period for the virus ranges from three to 17 days, during which time an infected individual may not show symptoms but still carry the virus. Common symptoms include a painful rash, which can appear on various parts of the body such as the face, hands, feet, chest, and genitals.
To mitigate the risk, the CDC recommends vaccination with the Jynneos vaccine, particularly for high-risk groups. These include sexually active gay and bisexual men and individuals who have been in close contact with confirmed Mpox cases. The Jynneos vaccine requires two doses for optimal protection and has proven effective in preventing severe symptoms.
In response to this first severe case, California health officials are implementing targeted contact tracing to identify any individuals who may have been exposed to the virus. Testing is underway for those who interacted with the patient, and public health guidelines are being reinforced to ensure containment. Officials are also closely monitoring developments in other countries where similar cases have occurred among travelers.
Though isolated cases of Mpox linked to international travel have been detected in nations like India, Sweden, and Thailand, U.S. officials aim to prevent any escalation. The CDC remains in close contact with global health organizations to track the spread of Mpox and update guidelines as necessary. The aim is to stay ahead of the virus, ensuring that the U.S. remains prepared for any potential outbreaks.
Vaccination campaigns are being prioritized in at-risk communities, focusing on educating the public about symptoms, modes of transmission, and the importance of early detection. The Jynneos vaccine, though originally limited in supply, has been scaled up to ensure sufficient coverage for those most vulnerable.
At present, no additional cases linked to the California patient have been identified. This situation reflects the current challenge facing global health systems as they deal with the evolving nature of infectious diseases, particularly those with changing transmission patterns like Clade Ib. Public health officials are urging caution but remain optimistic that early detection and swift containment measures can effectively manage this case.