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Last updated: 11/19/2024
Years published: 1986, 1994, 2003, 2005, 2009, 2024
NORD gratefully acknowledges Gioconda Alyea, MD (FMG), MS, National Organization for Rare Disorders, for assistance in the preparation of this report.
Yaws is a chronic, disfiguring and debilitating tropical infectious disease that primarily affects children. It targets the skin, bones and cartilage and only affects humans. The disease spreads from person to person through direct contact.
Yaws belongs to a group of infections known as endemic treponematoses, caused by spiral-shaped Treponema bacteria which also cause endemic syphilis (bejel) and pinta. Of these, yaws is the most common.
Yaws primarily affects poor, rural communities in warm, humid, tropical forest areas of Africa, Asia, Latin America and the Pacific. Poverty, low socioeconomic status and poor hygiene facilitate its spread.
Yaws begins with a wart-like lesion (papilloma) containing bacteria which can ulcerate if untreated. The secondary stage presents with yellow raised lesions or pain in long bones (dactylitis). Lesions are highly infectious and without treatment the disease can spread rapidly.
Yaws is very common in tropical areas of the world, but it is not known in the United States. It is not a sexually transmitted disease. It occurs in children younger than 15 years of age.
A single oral dose of azithromycin, an inexpensive antibiotic, effectively cures yaws.
Yaws initially presents as a papilloma teemed with bacteria. Papilloma and ulcers are very infectious and in the absence of treatment can quickly spread to others. Other clinical forms of yaws exist but they are not as infectious.
Secondary yaws occurs weeks to months after the primary infection and typically presents with multiple raised yellow lesions or pain and swelling of long bones and fingers (dactylitis).
There are two main stages of yaws infection:
In between primary and secondary or secondary and tertiary stages, a latent period occurs, where serologic exams are positive but where there are no signs and symptoms.
A third stage historically occurred in 10% of untreated people; however, due to surveillance and available antibiotics, it is now rarely seen. Late lesions may occur 5 to 10 years after inoculation. Skin symptoms are the most common and are typically near joints with ulcerative necrotic nodules. Facial damage historically has been a marked manifestation, affecting the area around the nose (paranasal swelling) with other classic late findings including painful sores in the joints (gummas), bowed tibia (saber shins), nasal cartilage destruction (gangosa) or exostosis of the paranasal maxilla (gondou).
Yaws is an infectious disease caused by a spiral-shaped bacterium (spirochete) known as Treponema pertenue which belongs to the same group of bacteria that causes venereal syphilis.
Yaws is usually transmitted by direct contact with the infected skin sores of affected individuals. In some cases, yaws may be transmitted through the bite of an infected insect.
The incubation period is 9–90 days, with an average of 21 days. Humans are the only source of infection. There is no natural immunity to yaws, and there is no vaccine to prevent it.
Yaws is a common infectious disease among children living in the tropical areas of Africa, South and Central America, the West Indies, and the Far East. It is not known in the United States. Yaws affects males and females in equal numbers and is most common in children between the ages of six and 10.
The prevalence of yaws declined greatly following a mass treatment campaign with penicillin by the World Health Organization (WHO) in the 1950s and ’60s. However, there has been a resurgence of yaws in certain countries in Africa and Southeast Asia.
The WHO categorizes countries into three groups based on yaws endemicity:
In 2013, the WHO identified 13 countries as yaws endemic. In 2020, WHO received reports of 87,877 suspected yaws cases from 11 countries, but only 346 were laboratory-confirmed from 7 countries, mainly in the Western Pacific Region (e.g., Papua New Guinea, Solomon Islands and Vanuatu). In 2021, the reported cases rose to 123,866 from 13 countries, with 1,102 confirmed cases across 9 countries, again predominantly in the West Pacific Region. However, many cases in this region lack laboratory confirmation.
In the United States only three cases of yaws were reported between 1921 and 1923.
Yaws initially presents as a wart-like tumour (papilloma) teemed with bacteria which makes clinical diagnosis straightforward. Without treatment, the papilloma will ulcerate. The diagnosis of the ulcerative form is more challenging and requires serological confirmation.
The diagnosis of stage 1 and stage 2 yaws is made by microscopic examination of tissue samples (darkfield examination) from the skin lesions of affected individuals.
Traditional diagnostic tools for yaws include laboratory-based serological tests like the Treponema pallidum particle agglutination (TPPA) and rapid plasma reagin (RPR). Although commonly used to diagnose treponemal infections (e.g., yaws and syphilis), these tests cannot differentiate between yaws and syphilis, necessitating thorough clinical evaluation in yaws-endemic areas, especially as 40% of lesions identified as yaws are caused by Haemophilus ducreyi bacteria.
Rapid Treponemal Tests: These widely available tests also cannot distinguish between past and current infections, limiting their usefulness for tracking transmission. However, the Dual Path Platform (DPP) Syphilis Screen and Confirm assay can detect both past and current infections, which makes it beneficial for accurate diagnosis in yaws management. Given the high cost of the DPP, many countries use traditional rapid tests for initial screening and reserve DPP testing for confirming positive cases, though the DPP can be used alone if resources permit.
Polymerase Chain Reaction (PCR): PCR testing provides definitive confirmation by detecting the DNA of Treponema pallidum pertenue directly from skin lesions. PCR is also instrumental in monitoring azithromycin resistance, which is essential for assessing effectiveness after mass drug administration and for ongoing surveillance post-elimination.
Treatment
Yaws can be effectively treated with either of two antibiotics:
Affected people should be reexamined 4 weeks after antibiotic treatment with over 95% achieving complete clinical healing. For cases of suspected treatment failure, macrolide resistance testing is required, followed by treatment with benzathine penicillin.
No vaccine exists for yaws, so prevention relies on health education and hygiene improvements to reduce transmission. All close contacts of yaws patients should be treated.
The recommended approach for yaws eradication is mass treatment, or total community treatment (TCT) where oral azithromycin (30 mg/kg, maximum 2 g) is given to at least 90% of the population in affected areas.
Eradication criteria include:
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Toll free: (800) 411-1222
TTY: (866) 411-1010
Email: [email protected]
Some current clinical trials also are posted on the following page on the NORD website: https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/
For information about clinical trials sponsored by private sources, contact: www.centerwatch.com
For information about clinical trials conducted in Europe, contact: https://www.clinicaltrialsregister.eu/
JOURNAL ARTICLES
Zoni AC, Saboyá-Díaz MI, Castellanos LG, Nicholls RS, Blaya-Novakova V. Epidemiological situation of yaws in the Americas: A systematic review in the context of a regional elimination goal. PLoS Negl Trop Dis. 2019;13(2):e0007125. Published 2019 Feb 25. doi:10.1371/journal.pntd.0007125
INTERNET
Maxfield L, Corley JE, Crane JS. Yaws. [Updated 2023 Jul 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526013/ Accessed Nov 19, 2024.
Yaws. World Health Organization. 12 January 2023. Available from: https://www.who.int/news-room/fact-sheets/detail/yaws Accessed Nov 19, 2024.
Yaws (Endemic treponematoses). World Health Organization. Available from: https://www.who.int/health-topics/yaws#tab=tab_1 Accessed Nov 19, 2024.
Yaws. MedlinePlus. Update Date: 12/31/2023. https://medlineplus.gov/ency/article/001341.htm Accessed Nov 19, 2024.
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