Endemic treponematoses (Yaws)

Bacterial infection caused by spirochetes called treponemes cause endemic treponematoses (mostly yaws). Humans are the only reservoir of this bacterial infection and since this disease is transmitted through direct (person-to-person) nonsexual contact, it tends to become epidemic in densely populated, unhygienic environments. Infection without treatment results in bumps and swelling as well as, occasionally, chronic disfigurement and disability.

<Yaws patient with elbow joint tumor, eight months after infection> CDC

Causes of Infection

Humans are the only reservoir of endemic treponematoses. This bacterial infection (mostly yaws) is caused by spirochetes called treponemes. Chronic bacterial infections from treponemes can include syphilis, which is sexually transmitted, and endemic treponematoses. Among frambesia, bejel, and pinta, the three types of endemic treponematoses, frambesia is the most common.
Yaws is transmitted via fluid from the lesion of an infected person through direct interpersonal nonsexual contact. Most lesions appear on the limbs. About 75% of those affected are children under 15 who have frequent contact with others, with the highest incidence in children aged 6-10.

Disease Agent:Spirochetes called treponemes

Intermediate Host:Humans


Infection without treatment results in bumps and swelling and, occasionally, chronic disfigurement and disability.
Early (infectious) and late (noninfectious) are the two basic stages of yaws, as outlines below.

Early phase: Infectious stage

In the early stages, an initial papilloma (circular, solid swelling on the skin with no visible fluid) develops where the spirochete first entered the body. Before healing naturally, the papilloma is full of the spirochetes and may last for three to six months. When left untreated, disseminated skin lesions over the body will occur in the next stage of the disease. Papules up to a centimeter across (solid elevations of the skin with no fluid visible) and macules (discolored flat skin patches without any sensory loss, similar to freckles) also occur in early yaws. The early stage of yaws is characterized by thickening and darkening of palms and the soles of the feet. Bone pain may also develop during this stage.

Late phase: Non-infectious stage

Late yaws, occurring five years after initial infection, is characterized by nose and bone disfiguration as well as palmar/plantar hyperkeratosis (thickening of the palms and soles of the feet). Thickened soles can also make walking difficult, adversely impacting day-to-day life.


Two antibiotics are used to treat yaws:

  1. Azithromycin is the first and preferred line of treatment because it is easy to administer.
  2. Benzathine penicillin is used when azithromycin is unavailable or cannot otherwise be used.


As there is no vaccine for yaws, prevention is carried out through interruption of the transmission via early diagnosis as well as mass drug administration for affected populations or communities. Needless to say, the essential aspects of prevention are health education and improved personal hygiene.

Regions at High Risk of Infection

Yaws infection is often found in environments that are densely populated and/or unhygienic. Yaws is epidemic in at least 13 countries, mainly victimizing children younger than 15 years old. It is most common in tropical forest regions in Asia, Africa, Latin America, and the western Pacific.

Estimated Number of the People Infected

According to a report published in 2015, it is estimated 89 million people live in 13 endemic countries.

Estimated Number of Deaths

While endemic treponematoses disfigure physical appearance and can lead to physical disability, it is not fatal. As such, there are no statistics available on deaths resulting from this disease.


WHO- Neglected Tropical Diseases, accessed March 19, 2014,

CDC- Neglected Tropical Diseases, accessed March 19, 2014,

Editorial Supervisors
Tsutomu Takeuchi, Professor Emeritus of Keio University
Hiroyoshi Endo, Professor Emeritus of St. Luke's International University