A potent strain of the monkeypox virus has acquired the ability to transmit through sexual contact, as indicated by new data. This development has unsettled researchers, who are concerned about a recurrence of the global monkeypox outbreak of 2022.
Records from previous outbreaks suggest that this strain, known as clade I, is more lethal than the one responsible for the 2022 worldwide outbreak. Clade I has historically caused sporadic outbreaks, typically confined to a few households or communities, within Central Africa. Instances of sexually transmitted clade I infections had not been documented prior to 2023.
However, since then, a clade I variant with an apparent capability for sexual transmission has instigated a cluster of infections in a conflict-affected area of the Democratic Republic of the Congo (DRC) in Central Africa. A preprint released on 15 April discloses that this outbreak is linked to 241 suspected and 108 confirmed cases — figures likely to be significantly underestimated due to limited testing capacity. Nearly 30% of the confirmed cases involved sex workers.
Furthermore, the region is grappling with a humanitarian crisis, while the DRC is battling the rampant spread of other diseases, such as cholera. This combination heightens the risk of the outbreak expanding beyond its current confines, asserts Anne Rimoin, an epidemiologist at the University of California, Los Angeles, who has been involved in monkeypox outbreak research in the DRC since 2002.
Unheeded warnings
The monkeypox virus can induce painful, fluid-filled lesions on the skin and, in severe instances, result in death. (Despite being renamed ‘mpox’ in 2022, the virus retains its original designation as ‘monkeypox virus.’) The virus persists in wildlife across multiple African nations, including the DRC, occasionally spilling over into human populations.
The initial significant outbreak involving human-to-human transmission, documented in Nigeria in 2017, yielded over 200 confirmed cases and 500 suspected cases of the illness. Researchers cautioned at that time that the virus might have evolved to spread through sexual contact.
Regrettably, their cautions went unheeded; in 2022, a global epidemic driven partly by sexual contact prompted the World Health Organization (WHO) to declare it a public health crisis. This ongoing epidemic is caused by a variant of the monkeypox virus known as clade II, which is less fatal than clade I, having infected over 94,000 individuals and claimed more than 180 lives.
While global cases of mpox infections have declined since 2022, there has been an upward trend in the DRC: in 2023 alone, the nation reported over 14,600 suspected cases and more than 650 fatalities. In September 2023, a fresh cluster of suspected cases emerged in the South Kivu province of the DRC. This particular cluster is of significant concern to researchers as it has primarily spread among sex workers, indicating that the virus may have adapted to efficiently transmit through sexual contact.
According to Nicaise Ndembi, a virologist at the Africa Centres for Disease Control and Prevention based in Addis Ababa, this could lead to accelerated human-to-human transmission, potentially with minimal symptoms. “The DRC is bordered by nine other countries — we're playing with fire here,” he warns.
Health authorities are deeply troubled, prompting representatives from the DRC and 11 neighboring nations to convene earlier this month to devise a response plan and pledge to enhance virus surveillance. With only around 10% of suspected mpox cases in the DRC tested in 2023 due to limited testing capabilities, health officials lack a comprehensive understanding of the situation, Ndembi notes.
Analysis of the virus responsible for the outbreak indicates mutations such as the deletion of a substantial portion of the virus’s genome, a phenomenon previously recognized as indicative of monkeypox viral adaptation. Consequently, the authors of the study have assigned a new designation to the strain circulating in the province: clade Ib.
Compounding the situation, South Kivu shares borders with Rwanda and Burundi, contending with “conflict, displacement, food insecurity, and challenges in providing adequate humanitarian assistance”, which “may create favorable conditions for further mpox transmission”, cautioned the WHO last year.
Vaccines and treatment needed
In 2022, numerous affluent nations extended offers of smallpox vaccines, which also confer protection against mpox, to high-risk individuals. However, minimal vaccine supplies have reached African nations, where the disease has historically exacted its highest toll.
While the DRC deliberates on regulatory approval for these vaccines, the United States has pledged to furnish the DRC with adequate doses to vaccinate 25,000 individuals, with Japan also committing to vaccine provision, reports Rosamund Lewis, the technical lead for mpox at the WHO in Geneva, Switzerland. Yet, a vaccination campaign in the DRC would necessitate hundreds of thousands — if not millions — of doses to immunize those most susceptible to infection, she remarks.
The extent of protection offered by these vaccines against clade I mpox remains uncertain, although Andrea McCollum, a poxvirus epidemiologist at the US Centers for Disease Control and Prevention in Atlanta, Georgia, suggests that animal test data are encouraging. Furthermore, researchers are conducting a trial in the DRC involving tecovirimat, an antiviral believed to be effective against mpox. McCollum anticipates receiving results within the next year.
To facilitate swifter disease diagnosis in the DRC, particularly in rural regions, the WHO and CDC have assisted in procuring equipment, notes Lewis. She expresses optimism, citing the prompt mobilization of African health authorities, that the outbreak can be contained before clade Ib mpox extends beyond its current boundaries.
doi: https://doi.org/10.1038/d41586-024-01167-5
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