Yaws is a chronic, contagious, non–venereal disease caused by the T pertenue and other various factors, usually beginning in early childhood. It resembles syphilis in its clinical features and is characterized by a primary skin lesion (mother Yaw) followed by a generalized eruption and a late stage of destructive lesions of the skin and bone. Yaws is also known as pian, bubas or framboesia.

Geographic distribution and prevalence
Yaws is exclusively confined to the belt of the Tropic of Cancer. Not long ago, it was a significant public heath problem in Africa, South–East Asia and Central America. Recent reports reveal marked variations in prevalence and patchiness in distribution in the former endemic areas. In Africa (e.g. Benin, Ghana and the Ivory Coast), there has been a great resurgence of Yaws. In the Americas, reported incidence of Yaws is very low with small foci remaining in Brazil, Columbia, Ecuador, Guyana and Surinam. In Asia, it occurs in Indonesia, Papua New Guinea and the South Pacific. Persistent, low levels of Yaws has been reported in Sri Lanka and India.

In the 1960s, the total world prevalence was estimated at being between 50 and 100 million active Yaws among the 400 million people living in the affected area. Due to intensive, mass treatment campaigns supported by WHO and UNICEF since the early 1950s, there has been a great reduction in the prevalence of Yaws. For example, in Fiji, the prevalence of active Yaws dropped from 28.1% in 1957 to 0.008% in 1966. Similarly, Yaws has declined in all other countries, but has not yet been eradicated, from any large geographical area. In fact, in some countries, due to relaxation of control efforts, the incidence of Yaws has recently been on the rise. As of 1976, the estimated cases of active Yaws were between one and two million. The continued presence of a few infected, cases does hold a constant threat of resurgent Yaws, which is already taking place in several countries.

Problem in India
Prior to the mass campaign of the 1950s, Yaws was endemic in Andhra Pradesh, Madhya Pradesh, Maharashtra, Orissa and Tamil Nadu. A survey (1985), suggests that Yaws continues to occur in India, although at a lower level, in at least three states, viz. Andhra Pradesh, Madhya Pradesh and Orissa, a total of 1,349 Yaws cases were diagnosed in these three states between 1983 and mid–1985. The affected districts were: West Godavari, Khammam and Vizianagaram in Andhra Pradesh, Bastar in Madhya Pradesh, and Keonjarh, Mayurbhanj, Denkanel, Phulbani, Balasore, and Koraput in Orissa. Whereas, in Andhra Pradesh Yaws occurred exclusively among the tribal population, in Orissa and Madhya Pradesh, both tribal and non–tribal populations were affected. In 1995, the National Institute of Communicable Diseases (NICD) submitted to the Government of India, a project document on the Yaws Eradication Programme. The Programme was initially approved in 1996 as a pilot project, in a district reporting the highest number of cases in Orissa. Based on the lessons learnt, the programme was expanded to cover all endemic areas of the country in March 1999. The problem of Yaws now is one of either “Residual yaws” or “Recrudescence” of Yaws due to continued low levels of transmission in some area which has to be controlled and eradicated. Only serological surveys will provide a valid measurement of the problem.

Incubation Period of Yaws
The incubation period for the disease is about three to five weeks.