Yaws Disease · What It Is, Presentation, Treatment and More

Yaws disease is a chronic, infectious skin condition caused by the spirochete bacterium Treponema pallidum subspecies pertenue, a subspecies of Treponema pallidum (T. pallidum). It primarily affects children under 15 years of age, though adults may also be affected. Yaws is the most common endemic treponematoses, which are chronic bacterial infections caused by spiral bacteria of the genus Treponema. Other endemic treponematoses include bejel caused by T. pallidum subspecies endemicum and pinta caused by Treponema carateum. These organisms are indistinguishable from Treponema pallidum subspecies pallidum which causes venereal (i.e., sexually transmitted) syphilis. Endemic syphilis, however, is considered non-venereal and is not sexually transmitted nor passed from mother to baby.  

Yaws disease is found in tropical areas of Africa, Southeast Asia, South America, and the Pacific Islands, particularly in impoverished, rural communities with limited healthcare access. According to the World Health Organization, 15 countries are known to be endemic to yaws disease and over 80,000 cases of yaws disease are diagnosed each year. 

Yaws disease can impact the skin, bones, and joints, and has an incubation period, or the time between exposure and appearance of symptoms, from 9 to 90 days. It typically begins with cysts, ulcers, and sores that can spread and progress through four different stages. The stages of yaws include primary, secondary, latent, and tertiary (late). The primary stage, known as primary yaws, is when the first skin lesion appears, often referred to as the “mother yaw.” This growth typically starts as a small, painless papule (i.e., a raised bump <1 cm in diameter) typically on the legs or feet, but can appear anywhere on the body. It may then develop into a large yellow nodule (i.e., a raised bump 2 to 5 cm in diameter, often called papilloma) that eventually ulcerates. The ulcer  may have a texture resembling a strawberry, that eventually crusts over and heals, often leaving a scar. Alternatively, primary yaws can also appear as a cluster of papules. This stage may last anywhere from 3 to 6 months.  

The secondary stage, or secondary yaws, typically occurs weeks to months after the primary infection but may develop up to 2 years later. Secondary yaws symptoms are characterized by multiple skin lesions that may cover the hands, arms, legs, feet, buttocks, and face. If the soles of the feet are involved, walking may be painful, known as “crab yaws.” These skin lesions vary in appearance and may be wart-like, ulcerative, raised, bumpy, red or yellow, scaly, flat, hard, or thickened. In this stage, yaws disease can spread to the bones, causing pain and swelling in the fingers, toes, arms, or legs.   

The third stage, known as latent yaws, involves the long bones, joints, and/or skin. During this stage, individuals may test positive for Treponema pallidum, without exhibiting signs or symptoms. This latent period may last for several years, and an individual may still be contagious during this stage. Approximately 10% of individuals may develop tertiary or late yaws, 5 to 10 years after the primary stage. This stage is marked by widespread growth, including large lesions near joints, deep open wounds, and plaques on the hands and feet.  

People with yaws may exhibit additional symptoms including swollen lymph nodes, bone pain, general tiredness, and malaise. If left untreated, yaws disease may return months or years later, and lead to permanent damage to the skin, bones, and tissues. Complications of yaws disease may involve swollen fingers and toes, called dactylitis; infection of bones or their lining referred to as periostitis; tissue death; disfigurement; secondary bacterial infections; and physical limitations caused by plaques or other damage. Yaws may also be complicated by gangosa, an ulcerative condition resulting in destruction of the soft palate, spreading to the bone, cartilage, and soft tissue of the face, specifically the nasal structures.  

Yaws disease is often diagnosed by a healthcare professional through a thorough history, including a review of symptoms, past medical history, and recent travel history, followed by a physical examination looking for characteristic skin lesions. Specific laboratory tests can be used to aid in the diagnosis of yaws including Treponema pallidum particle agglutination (TPPA) and rapid plasma reagin (RPR) blood tests. However, these tests are often used for screening purposes and are unable to distinguish between yaws disease and other forms of syphilis, therefore the interpretation of results requires concurrent clinical assessment. More specific treponemal tests, such as the fluorescent treponemal antibody absorption (FTA-ABS) test, confirms the presence of antibodies specific to Treponema pallidum, but cannot differentiate between past and current infections, as test results remain positive for life once antibodies are present. 

The dual path platform syphilis screen and confirm (DPP) assay can detect both past and present infections, offering a more comprehensive diagnostic approach. Due to its high cost, initial screening of suspected cases of yaws may be performed with less expensive treponemal tests, with positive results being subsequently confirmed by the DPP. Polymerase chain reaction (PCR) technology provides definitive confirmation of yaws disease by detecting DNA in skin lesions. 

Swabs of skin lesions and blood tests may be analyzed for microbiological examination. Under a microscope, the bacteria causing yaws disease and venereal syphilis appear identical, making differentiation based on microscopy challenging. Yaws disease may be considered a diagnosis of exclusion, and accurate diagnosis requires a combination of clinical exam findings and laboratory testing. 

Yaws disease is treated with antibiotics that can be given at any stage. The preferred treatment is a single high dose of azithromycin. Alternatively, a single high dose of benzathine penicillin G may also be considered for individuals who have suspected treatment failure with azithromycin or those who cannot receive azithromycin (e.g., due to allergies). Early treatment, particularly during the first and second stages of yaws, generally results in a positive prognosis and significantly reduces the risk of complications such as spreading, permanent scarring, and disfigurement. Individuals should be re-examined 4 weeks after antibiotic treatment. In cases of presumed treatment failure, macrolide resistance testing may be conducted, and treatment with benzathine penicillin may be considered. 

Since there is no vaccine for yaws disease, prevention involves avoiding skin-to-skin contact with individuals who are known to have the condition. Healthcare providers may also administer antibiotics to close contacts of affected individuals to prevent the spread of infection. The World Health Organization is actively working towards the eradication of yaws disease by treating entire communities in endemic areas, regardless of whether individuals exhibit symptoms, to control and eventually eliminate the condition.