Yaws (also Pétasse tropica, thymosis, polypapilloma tropicum, pian or parangi) is a tropical infection of the skin, bones and joints caused by the spirochete bacterium Treponema pertenue. Other treponematosis diseases are bejel (Treponema endemicum), pinta (Treponema carateum), syphilis (Treponema pallidum), and Lyme Disease (Borrelia burgdorferi).
The largest group afflicted by yaws are children aged 6 to 10 years in tropical areas of the Americas, Africa, Asia or Oceania. There were World Health Organization funded campaigns against yaws from 1954 to 1963 which greatly reduced the incidence of the disease, although more recently numbers have risen again.
The disease is identified from blood tests or by a lesion sample through a darkfield examination under a microscope. Treatment is by a single dose of penicillin, erythromycin or tetracycline, recurrence or relapse is uncommon.
Examination of ancient remains has led to the suggestion that yaws has affected hominids for the last 1.5 million years. The current name is believed to be of Carib origin, "yaya" meaning sore; frambesia is a Modern Latin word inspired by the French word framboise ("raspberry").
Yaws was nearly eradicated by a worldwide treatment program in the 1950s, which reduced the number of sufferers of yaws from an estimated 50 million to nearly zero. However, the World Health Organization reported in January 2007 that yaws is on the rise again, with roughly a half a million sufferers, mostly in poor, rural areas.