The spread of mpox in Africa needs to be addressed urgently, the World Health Organization (WHO) said on Tuesday, as scientists warned separately of a dangerous strain in the Democratic Republic of Congo.

"There is a critical need to address the recent surge in mpox cases in Africa," Rosamund Lewis, the WHO's technical lead for mpox, said in a briefing note to journalists.

In a separate briefing, John Claude Udahemuka of the University of Rwanda, who has been working on an outbreak in Congo's hard-to-reach South Kivu province, said the strain spreading there - a mutated version of the clade I mpox endemic in Congo for decades - was extremely dangerous. It has fatality rates of around 5% in adults and 10% in children.

This year, roughly 8 600 mpox cases have been reported in Congo, and 410 deaths, Cris Kacita, the doctor in charge of operations in the country's mpox control programme, told Reuters last week.

Mpox is a viral infection that spreads through close contact, causing flu-like symptoms and pus-filled lesions. Most cases are mild but it can kill.

A different, less severe form of the virus - clade IIb - spread globally in 2022, largely through sexual contact among men who have sex with men. This prompted the WHO to declare a public health emergency. Although that has ended, Lewis said on Tuesday the disease remained a health threat. Two people died in South Africa this month of this form of the virus after a handful of cases were diagnosed.

Vaccines and treatments were used to combat the global outbreak, but they are not available in Congo.

The WHO and scientists said efforts were ongoing to address that.

In South Kivu, Adahemuka and other researchers said the new strain was spreading partly by sexual contact among men and women, and particularly among sex workers.

He said other close contact routes needed study, with evidence of transmission at school and from caregiver to child. The disease also seemed to be causing miscarriages among pregnant women as well as a longer-term rash and other lingering symptoms, the team said.

Leandre Murhula Masirika, research co-ordinator in the health department in South Kivu province, said 20 cases were arriving at hospital in the mining town of Kamituga every week.

"At the rate things are going, we risk becoming a source of cases for other countries," said Kacita. South Kivu borders Rwanda and Burundi.

He said 24 of 26 provinces in Congo were affected and the outbreak was the worst mpox epidemic yet.