Yaws is a tropical infection of the skin, bones, and joints caused by the spirochete bacterium Treponema pallidum pertenue.

After weeks to years, joints and bones may become painful, fatigue may develop, and new skin lesions may appear.

[11] Although one of the first descriptions of the disease was made in 1679 by Willem Piso, archaeological evidence suggests that yaws may have been present among human ancestors as far back as 1.6 million years ago.

[10] Yaws is classified as primary, secondary, and tertiary; this can be clinically useful, but infected patients often have a mix of stages.

It begins as multiple, pinhead-like papules; these initial lesions grow and change in appearance and may last weeks before healing, with or without scarring.

[2] Secondary yaws typically shows widespread skin lesions that vary in appearance, including "crab yaws" (areas of skin of abnormal color) on the palms of the hands and soles of the feet[12] (named for the crab-like gait they cause people with painful soles to assume[2]).

[citation needed] These secondary lesions frequently ulcerate and are then highly infectious, but heal after 6 months or more.

[12] After primary and secondary yaws (and possibly, in some cases, without these phases), a latent infection develops.

[2] Rhinopharyngitis mutilans,[14][15] also known as gangosa, is a destructive ulcerative condition that usually originates about the soft palate and spreads into the hard palate, nasopharynx, and nose, resulting in mutilating cicatrices, and outward to the face, eroding intervening bone, cartilage, and soft tissues.

[10] The initial yaws wound contains infectious bacteria, which are passed onto others through skin-to-skin contact, typically during play or other normal childhood interactions.

[10][16] Early (primary and secondary) yaws lesions have a higher bacterial load, thus are more infectious.

[10] T. pallidum pertenue has been identified in nonhuman primates (baboons, chimpanzees, and gorillas) and experimental inoculation of human beings with a simian isolate causes yaws-like disease.

[2] A microscopic examination of a biopsy of a yaw may show skin with clear epidermal hyperplasia (a type of skin thickening) and papillomatosis (a type of surface irregularity), often with focal spongiosis (an accumulation of fluid in a specific part of the epidermis).

Treponemal tests are more specific, and are positive for anyone who has ever been infected with yaws; they include the Treponema pallidum particle agglutination assay.

Nontreponemal assays can be used to indicate the progress of an infection and a cure, and positive results weaken and may become negative after recovery, especially after a case is treated early.

[12] They include the venereal disease research laboratory (VDRL; requires microscopy) and rapid plasma reagin (RPR; naked-eye result) tests, both of which flocculate patient-derived antibodies with antigens.

[17] Haemophilus ducreyi infections can cause skin conditions that mimic primary yaws.

[2] Treatment is normally by a single intramuscular injection of long-acting benzathine benzylpenicillin, or less commonly by a course of other antibiotics, such as azithromycin or tetracycline tablets.

[2] Primary and secondary lesions usually heal in 2–4 weeks; bone pain may improve within two days.

[2] Primary and secondary stage lesions may heal completely, but the destructive changes of tertiary yaws are largely irreversible.

As of 2015[update], it is estimated that about 89 million people live in yaws-endemic areas, but data are poor, and this is likely an overestimate.

[22] In the early 1900s, yaws was very common; in sub-Saharan Africa, it was more frequently treated than malaria, sometimes making up more than half of treatments.

[24] Examination of remains of Homo erectus from Kenya, which are about 1.6 million years old, has revealed signs typical of yaws.

The causative agent of yaws was discovered in 1905 by Aldo Castellani in ulcers of patients from Ceylon.

[6] The current English name is believed to be of Carib origin, from "yaya", meaning sore.

[17] Towards the end of the Second World War, yaws became widespread in the North of Malaya under Japanese occupation.

[26] However, "premature integration of yaws and other endemic treponematoses activities into weak primary health-care systems, and the dismantling of the vertical eradication programmes after 1964, led to the failure to finish with the remaining 5% of cases"[26] and also led to a resurgence of yaws in the 1970s, with the largest number of case found in the Western Africa region.

Although a single injection of long-acting penicillin or other beta lactam antibiotic cures the disease and is widely available and the disease highly localised, many eradication campaigns ended in complacency and neglect; even in areas where transmission was successfully interrupted, re-introduction from infected areas occurred.

[29] In the Philippines, yaws stopped being listed as a notifiable disease in 1973; as of 2020, it is still present in the country.

[40][41] A WHO meeting report in 2018 estimated the total cost of elimination to be US$175 million (excluding Indonesia).