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More mpox diagnostic kits and a proactive approach to community testing is needed to stop Sierra Leone’s growing outbreak, researchers say.

The mpox outbreak began late last year in the small coastal town of Lungi, in northern Sierra Leone, after a man visiting the town had sex with a hotel worker and developed high fever, muscle and body pains, with swollen lymph nodes. He was later transferred to the capital Freetown, where he was diagnosed positive for mpox. Surprisingly, after contact tracing was done, no one, including his wife, tested positive. Health authorities could not trace the hotel worker.

Over the following six months, the virus sped through all four administrative regions of Sierra Leone, and by 1 July 2025, there were around 4500 confirmed cases of mpox and 29 deaths in the country – accounting for roughly half of all confirmed Mpox cases in Africa. Now, the virus is changing as it spreads to neighbouring countries. In early June 2025, Liberia reported 69 mpox cases and Ghana has recorded 108 cases as of 20 June. Ghana’s next-door neighbour, Togo, has also reported a steady rise in cases over the last 3 weeks, according to the Africa Centres for Disease Control and Prevention.

Jia Kangbai, an infectious diseases epidemiologist from Njala University in Sierra Leone, who diagnosed the index case says the outbreak is compounded by a critical shortage of diagnostic kits and testing capacity. Many confirmed cases are from a backlog of samples which may have been collected days earlier. Testing delays are due to limited testing sites, insufficient lab personnel, and resource shortages. By the time results are released, cases have already been spreading in the community.

For Kangbai and other researchers racing to stop the spread of the virus in Sierra Leone, these issues raise the possibility that it will spark a larger outbreak across west Africa’s densely populated region. In a genomic analysis posted on virological.org this May, scientists found that a fast-moving new variant of mpox called G.1 is circulating under the radar and quickly spreading. The virus, which may have already infected 11,000 people in the country, belongs to clade IIb, a variant that circulated for eight years in Nigeria before it caused a global epidemic, primarily among men who have sex with men.

The authors identified evidence of G.1 export from Sierra Leone, including two sequences sampled in the US in March and April 2025, and two samples from Germany in March, posing a broader risk beyond west Africa.

Their findings also indicate cryptic transmission – a situation whereby the virus is circulating at low levels within a population, but its source is difficult to identify – underscored the need to strengthen surveillance and diagnostics. “The response should be proactive rather than reactive,” says Allan Campbell, the laboratory manager at the Sierra Leonean Central Public Health Reference Lab (CPHRL).

The World Health Organization has donated laboratory reagents worth $26,400 to the Ghana Health Service (GHS) to boost the screening of confirmed mpox cases in the country. But disease researchers say countries in the west African region will need to heighten cross-border surveillance and testing.

Increasing testing could be a game-changer in identifying infected individuals and ensuring that the outbreak does not become an epidemic and even more widespread across the region and world, says John Demby Sandi, who heads the genomics and molecular laboratory at Kenema Government Hospital Lassa fever (VHF) research lab, in Kenema.