A virtually eradicated disease that eats through people's skin, cartilage and bones is reappearing in Africa, Asia and South America, the World Health Organization warned Thursday.

Yaws, which is triggered by bacterial infection and can cause debilitating deformations, particularly in children under 15, once affected 50 million people worldwide before a massive treatment program in the 1950s almost succeeded in wiping it out.

"What happened then is that people focused on other things and took their eye off yaws," WHO spokesman Ian Simpson said.

"The attempt now is to try and see what can be done to make sure that the number of cases doesn't increase and that a new effort is made to eradicate it," he said.

At present, some 500,000 people mostly in poor, rural areas are affected by yaws, according to WHO.

The global health body said it had assembled experts from countries where yaws is endemic in Geneva this week to consider whether to revive the global program of 50 years ago so as to "eradicate this disease once and for all."

The nonfatal disease, which is spread by spiral bacteria similar to those that cause syphilis, can be treated with a single dose of cheap penicillin.