Yaws is a chronic skin infection caused by a bacterium closely related to the one that causes syphilis. It spreads through direct skin-to-skin contact, primarily affects children in tropical regions, and can cause severe bone destruction if left untreated. As of 2024, 16 countries are considered currently endemic, and the World Health Organization has targeted the disease for global eradication by 2030.
What Causes Yaws
The infection is caused by a spiral-shaped bacterium called Treponema pallidum pertenue. It belongs to the same species as the bacterium behind syphilis, but it behaves differently: yaws is not sexually transmitted and does not pass from mother to child during pregnancy. Instead, it enters the body through small cuts, scrapes, or abrasions on the skin when a person comes into direct contact with an infected sore.
This makes yaws highly contagious in close-knit communities, especially among family members and playmates. Children between the ages of 2 and 15 are most commonly affected, largely because of frequent skin-to-skin contact during play and the minor wounds that come with childhood. The disease thrives in warm, humid, tropical environments, particularly in rural and isolated communities in Africa, Asia, Latin America, and the Pacific Islands. Poverty, overcrowding, and limited access to clean water and hygiene all help the infection spread.
Stages and Symptoms
Yaws progresses through distinct stages, much like syphilis, though the symptoms appear on the skin and bones rather than the genitals or internal organs.
Early Stage
The first sign is usually a single, painless bump at the site where the bacterium entered the skin. Over days to weeks, this grows into a raised, round sore that can become ulcerated and crusty. These initial lesions tend to appear on the legs, arms, or face. They are teeming with bacteria and extremely contagious. Without treatment, the sore typically heals on its own within a few months, but the infection remains in the body.
Secondary Stage
Weeks to months after the first sore heals, a secondary stage can develop. Multiple smaller sores appear across the skin, often near joints and on the thin skin covering bones. These lesions can be itchy and uncomfortable. Some people also develop thickened, cracked skin on the palms and soles, which can make walking painful. This stage can come and go over months or even years, with periods where the infection appears to go dormant (latent yaws) and then flares up again.
Late Stage
Historically, about 10% of untreated patients developed tertiary yaws, which appears 5 to 10 years after the initial infection. Thanks to antibiotics and better surveillance, this stage is now rarely seen, but its effects are devastating. The bacterium attacks bone and cartilage, creating deep ulcerative nodules near joints. One of the most disfiguring complications is gangosa, the destruction of nasal cartilage and surrounding tissue that can leave a gaping hole in the center of the face. Other classic late findings include saber shins (a visible bowing of the shinbones), bony growths around the upper jaw, and gummas, which are firm nodules that break down into chronic ulcers near joints. These changes are permanent and can severely limit a person’s ability to walk.
How Yaws Is Diagnosed
Diagnosis often starts with a visual assessment. In endemic areas, a trained health worker can recognize the characteristic sores, especially in children. However, yaws looks identical to other tropical skin infections under many circumstances, and the blood tests used to detect it cannot distinguish it from syphilis because both diseases are caused by near-identical bacteria. This is a significant challenge. In 2024, over 152,000 suspected yaws cases were reported to the WHO from 10 countries, but only 996 were laboratory-confirmed in 7 countries, precisely because routine lab testing is not yet widely available in the affected regions.
Rapid point-of-care blood tests exist and can detect antibodies to the Treponema bacterium within minutes using a finger prick. These are useful for screening in remote areas, but confirming an active infection (versus a past one) still requires additional testing that many rural clinics lack.
Treatment
Yaws is one of the more straightforward infectious diseases to treat. A single oral dose of the antibiotic azithromycin cures the infection in the vast majority of cases. This replaced the older approach of a painful injection of penicillin, which required trained health workers and sterile needles. The shift to a pill that can be swallowed once made mass treatment campaigns far more practical, especially in remote communities with limited medical infrastructure.
Early-stage yaws responds well, and sores heal completely without scarring in most cases. Even secondary-stage disease clears with treatment. The critical window is before the infection reaches the bones. Once tertiary yaws has caused bone destruction or cartilage loss, antibiotic treatment can stop further damage but cannot reverse what has already occurred.
Global Eradication Efforts
Yaws nearly disappeared once before. A massive WHO campaign in the 1950s and 1960s using injectable penicillin reduced global cases from around 50 million to about 2.5 million. But when funding dried up and surveillance lapsed, the disease crept back in several regions.
The current push, known as the Morges strategy, was launched in 2012 after the discovery that oral azithromycin works as well as injected penicillin. The original eradication target was 2020, but that proved overly ambitious, and 2030 is now the goal. The strategy has two phases. First, entire communities in endemic areas receive mass treatment: every resident, whether symptomatic or not, takes a single dose of azithromycin. This is typically repeated for two to three rounds. After that, health teams switch to targeted treatment, tracking down active cases and treating them along with their household members, schoolmates, and close contacts. These targeted rounds continue every 6 to 12 months until transmission stops.
The challenges are logistical more than medical. Many endemic communities are in remote, hard-to-reach areas. Surveillance gaps are enormous: 82 previously endemic countries and territories currently have an unknown status, meaning no one is sure whether transmission has stopped there or simply gone undetected. And because lab confirmation rates remain low, the true burden of yaws globally is almost certainly higher than reported numbers suggest.
Why Yaws Still Matters
Yaws is entirely preventable and easily curable, yet it persists because it affects some of the world’s poorest and most isolated populations. It causes no fatalities, which paradoxically works against it: diseases that don’t kill tend to attract less funding and attention than those that do. But for the children who develop chronic sores, painful cracked feet, or permanent bone deformities, the impact on quality of life is severe. Disfigurement from late-stage yaws also carries significant social stigma in affected communities.
The fact that a single pill can cure the disease, and that no animal reservoir complicates transmission, makes yaws one of only a handful of diseases considered realistically eradicable. Whether the 2030 target is met depends largely on sustained political will and funding for community-level treatment campaigns in some of the most underserved parts of the world.