Pygmies living in remote forests in the Republic of Congo are suffering from a "flesh-eating" disease, the New Scientist magazine reports.
The disease rarely kills but can cause severe disfigurement
Known as bush yaws or pian, it is rarely fatal, but infects cuts and causes lesions that destroy skin and bones.
A UN team that visited the Likouala region found that some 3,000 Pygmies there had the disease.
The highly contagious illness can be prevented by washing with soap and water and treated with penicillin.
But the team sent by the UN's children fund (Unicef) was only able to treat 135 people during its latest trip because of a lack of funding and the remoteness of the region.
The Unicef representative in the Congolese capital, Brazzaville, Raymond Janssens, told the BBC's Focus on Africa programme that the disease used to be present in all tropical areas.
"Yaws begins where the trail ends," he quoted one researcher from the 1950s as saying.
But improved hygiene and knowledge of the disease has meant that it has now been eliminated from many areas.
Mr Janssens said that the Unicef team had been conducting an education programme in the area as well as administering drugs.
Unicef hopes to send another mission to the area in June.