California has reported the first case of a new mpox strain that is spreading from person to person, marking a concerning development in the ongoing battle against this virus. The infected individual had recently traveled from Eastern Africa, where multiple countries are currently grappling with the transmission of this virus.
The infected person received treatment in a health facility in San Mateo County and is currently in isolation at home, according to a statement released by the California Department of Public Health. The Centers for Disease Control and Prevention also confirmed that the individual is not undergoing treatment with anti-mpox medication, which suggests that the infection may be mild.
The specific strain of the virus involved is known as clade Ib, a variant of clade I viruses that typically originate from an animal source in East Africa, where the virus naturally exists. It differs from the clade IIb virus responsible for the major international mpox outbreak that began in 2022.
Health authorities in California have stated that there is no evidence at this time to suggest that the infected person has transmitted the virus to others. Contact tracing efforts are underway to identify individuals who may have been in close contact with the infected individual.
The World Health Organization declared the ongoing person-to-person spread of mpox a Public Health Emergency of International Concern in August, following a similar declaration during the 2022 outbreak. Specimens from the California case have been sent to the CDC for further analysis.
Person-to-person transmission of clade Ib viruses was first identified in September 2023 in the Democratic Republic of the Congo. While most transmission is occurring in African countries, cases related to travel have been reported in several other countries, including Germany, India, Kenya, Sweden, Thailand, Zimbabwe, the United Kingdom, and now the United States.
The CDC has assessed the risk posed by the clade Ib outbreak in Central and Eastern Africa to the U.S. population as low, based on simulation exercises conducted. The simulations indicate that close-contact transmissions within households are unlikely to lead to a large number of mpox clade I cases in the United States.
Since the beginning of the year, over 115,000 mpox cases have been reported in at least 123 countries, with at least 255 fatalities. Mpox is related to smallpox, a virus that was eradicated in 1980. Mpox causes a blistering rash and can be fatal, although the fatality rate is lower compared to smallpox.
Historically, mpox cases were believed to be acquired through contact with infected animals in Africa. However, sexual transmission of the virus has been identified since 2022, primarily among communities of gay, bisexual, and other men who have sex with men. Vaccines such as Bavarian Nordic’s Jynneos can provide protection against mpox, but global production of these vaccines is limited.
The discovery of person-to-person transmission of the clade Ib virus in California underscores the importance of continued vigilance and public health measures to prevent the spread of this potentially dangerous virus.
