A surge of mpox infections in the small African nation of Sierra Leone has pummelled the country’s health-care system, raising the possibility that the virus will spread to neighbouring countries and spark a larger outbreak throughout the densely populated region of West Africa.
Sierra Leone has confirmed 15 deaths and more than 3,000 mpox infections — more than half of all new infections for Africa — over the past month. According to an analysis of 76 viral genomes posted on the discussion forum Virological.org on 28 May, the outbreak began in November. The work also suggests that there have been at least four times more infections than officials have reported, says Edyth Parker, a genomic epidemiologist at the Institute of Genomics and Global Health in Ede, Nigeria, who is a co-author.
“The situation is so dire — the number of cases keeps increasing rapidly,” says Jia Kangbai, an infectious-diseases epidemiologist at Njala University in Freetown, Sierra Leone. “Things are getting very challenging now.”
A surge in cases
The virus that causes mpox can lead to painful, fluid-filled lesions on the skin, and produce fever and, in severe cases, death. The virus, which is thought to persist in some wild rodent species, is endemic in several African countries, including Sierra Leone, and occasionally spills into people.
Health officials have been on high alert for surges of the virus that causes mpox ever since it spread to regions that it had never reached before, causing a global outbreak of the disease in 2022. That outbreak, which continues today at a slower pace, has infected more than 100,000 people, mainly men who have sex with men.
The virus that causes mpox (pink) is shown infecting a cell (green) in this colourized electron microscope image.
But the boom in infections in Sierra Leone has virologists worried once again: the country has reported a near-exponential growth in mpox cases that seem to be spreading from person to person, mainly among young people, both men and women. Epidemiological data suggest that sexual contact is a driver of the outbreak, because several sex workers have been infected and many people have reported genital lesions, according to a 27 May study posted on the preprint server medRxiv ahead of peer review1.
The surge in cases, which has been concentrated in Sierra Leone’s capital city of Freetown, is fuelled by the same strain, clade IIb, that caused the global outbreak, according to the Virological.org analysis. This shows that when mpox is “put into a densely populated area where you have these dense sexual networks, it can take off very easily”, says Jason Kindrachuk, a virologist at the University of Manitoba in Winnipeg, Canada, who co-authored the medRxiv preprint.
The number of reported infections is likely to continue increasing sharply, because Sierra Leone’s health-care system lacks the capacity to curb the outbreak, Kangbai says. He adds that the country is entering its rainy season, meaning that more people will congregate indoors, creating more opportunities for the virus to spread.
A lack of aid
This outbreak comes as several African countries continue to battle their own mpox outbreaks, putting pressure on resources across the continent. A concerning strain of the virus, called clade Ib, has gained the ability to spread through sexual contact, causing a boom in infections across Central Africa, especially in the Democratic Republic of the Congo (DRC), since 2024.
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