Yaws is a highly infectious skin disease caused by the bacterium Treponema pallidum (subspecies pertenue). This bacterium infects humans through direct skin-to-skin contact and triggers the formation of open sores (named ulcers) and noncancerous lumps (named papillomas) on the skin. If left untreated, the disease can cause bone deformities and loss of mobility in affected individuals.1 This disease mostly occurs in children, with around 75-80% of patients being under the age of 15, and affects both males and females equally.1
Yaws is considered a “neglected tropical disease” as it is a condition that is mainly found in tropical climates and in poor countries. Indeed, Yaws is mainly found in impoverished communities in the warm and humid areas of Africa, Asia, South America and the Western Pacific Region.1 There are currently 14 countries where Yaws is considered endemic (meaning it occurs regularly).2 These communities that are commonly affected by Yaw's outbreaks are mostly found in rural (countryside) areas and suffer from low socio-economic conditions, poor hygiene, and lack of health services, all of which facilitate the spreading of the disease.1
This article will outline the causes, symptoms, diagnosis and treatment options for Yaws. Moreover, it will explain how the World Health Organisation is aiming to eradicate the neglected tropical disease.
What does yaws look like?
The manifestation of Yaws can be divided into three phases: the primary, secondary and tertiary phases.3
The first phase of Yaws typically occurs in early childhood, with 6 years being the average age at which initial symptoms of the infection appear. The first symptom of the infection is an itchy, patchy papillom in the skin.3 This initial papilloma forms at the spot where the Treponema pallidum subspecies pertenue bacterium first enters the patient’s body – and is actually full of bacteria, which form a type of pus encased by a hard yellow crust. This papilloma is referred to as the “mother yaw” and commonly appears on patients' legs and feet.3 Without proper treatment, these initial lesions can grow into ulcers.3
The second phase of Yaws typically starts a month or two after the first phase (and up to two years after primary infection). In the secondary phase, lumps and ulcers similar to the “mother yaw”, all filled with pus and teeming with bacteria, appear and grow all over the body (including the face, arms, and genitals). Papillomas on the bottom of patients’ feet can produce painful ulcers, making it hard to walk. These ulcers are also known as “crab yaws”, due to the crab-like movements patients make when walking.3
If patients have not yet received treatment, their lymph nodes can become swollen. Further, infection can spread through the blood and to the bones of their fingers, toes, arms and legs, resulting in pain and swelling.4
The tertiary phase of Yaws only happens in roughly 10% of patients – typically in the ones who received no treatment during the first two phases of the infection. This tertiary stage occurs after a period of years where the infection remained “dormant” – and as such, patients have shown no symptoms. The third phase may start between 5 and 10 years after initial infection.3
In the tertiary stage of Yaws, painful lumps and ulcers appear all over the body, and they can go quite deep into the patient’s skin. However, these lesions do not contain any bacteria. Large growths close to bones and joints commonly occur, often leading to bones becoming infected. In turn, bone infections can result in the impairment of their function, as well as bone deformity and destruction.4
The third phase of Yaws can also cause a variety of new symptoms, including:3
- Paranasal swelling – The swelling of the tissues around the nose
- Hypertrophic osteitis – Additional growth of bones in the areas of the face where lumps grow
- Gangosa syndrome (also known as rhinopharyngitis mutilans) – Destructive changes to the nose, throat and roof of the mouth
What causes yaws?
A specific type (subspecies) of the bacterium from the spiral-shaped bacteria family Treponema pallidum causes yaws – the subspecies pertenue.5 Other Treponema pallidum family members are responsible for different diseases: subspecies pallidum causes syphilis, subspecies endemicum causes bejel, and Treponema carateum causes pinta. Along with Yaws, this group of infections are known as endemic treponematoses, with Yaws being the most common of them all.5
of Yaws transmission occurs in the first two phases of the infection when individuals come into direct skin-to-skin contact with infected individuals. Yaws are not contagious once a patient is in the tertiary phase of infection.5
Similarities and differences to other endemic treponematoses
There has been a debate for many years over the differences between the endemic treponematoses caused by the Treponema pallidum family, as the bacterial subspecies that cause these different infections are virtually identical, both genetically and structurally.5 This can make it quite difficult to make an accurate diagnosis. What distinguishes Despite this, the physical manifestation and transmission of Yaws distinguishes it from the other endemic treponematoses:5
- Yaws versus syphilis – Whilst Yaws primarily infects children under the age of 16, syphilis can occur in anyone at any age. Moreover, syphilis is transmitted by sexual contact, whereas Yaws is not. In addition, growths related to syphilis can affect tissues and organs, whereas Yaws growths only affect the skin and bones.6
- Yaws versus bejel – Bejel lesions are limited to the skin and do not affect the bones, unlike Yaws. Furthermore, bejel growths are mostly found on the face and around the mouth, as the infection is only transmitted via mouth-to-mouth contact (unlike Yaws).7
- Yaws versus pinta – Pinta is an infection that is found only in Central and South America and is, therefore, not as widespread as Yaws. In addition, pinta lesions do not develop into ulcers.7
It is important to know the differences between such bacterial infections in order to accurately diagnose and treat affected individuals.
In order to diagnose Yaws, a healthcare worker will assess the lumps of your skin via a dark-field examination. This involves taking samples from the lesions and assessing them under a microscope to look at the bacteria within them. However, due to the similarities between the bacteria that cause Yaws and the bacteria that cause syphilis, the identification of other symptoms (where the lesions are, how they were transmitted to the patient, etc.) is crucial for distinguishing the different infections.3
A series of laboratory tests can also be done to help make a diagnosis, including:
- Blood examinations, such as Treponema pallidum particle agglutination (TPPA) and rapid plasma reagin (RPR), are used to confirm a diagnosis of endemic treponematose8
- Polymerase chain reaction (PCR) technology, which can detect genetic material in samples of a patient’s papilloma to assess the presence of the Yaws-causing bacteria9
Whilst these tests can be used to reach a general diagnosis of an endemic treponematose, they are not specific for Yaws itself. Therefore, a definite Yaws diagnosis can only be reached by taking a detailed medical history and examining skin lumps. This is not the most objective method of diagnosis, and therefore, more specific assessments are required for accurate diagnosis of Yaws.
Treatments for yaws
Although there is no vaccine for Yaws, it can be effectively treated with antibiotics. The antibiotics used to treat Yaws include:
- Azithromycin – A single oral dose (taken via the mouth) of 30 milligrams per kilogram (up to a maximum dose of 2 kilograms)
- Benzathine penicillin – Administered as a single injection deep into the muscles at 0.6 million international units (I.U.) for children under 10 years of age and 1.2 million I.U. for anyone over 10 years
Patients prescribed either of these antibiotics are examined after four weeks of treatment. In 95% of cases, full recovery from Yaws occurs.10 These antibiotics are also commonly given to the family members of any affected children to prevent the disease from spreading.
Azithromycin is considered the preferred treatment, as it is much easier to administer to patients than benzathine penicillin.10 However, some infections are resistant to azithromycin. This is because azithromycin is a macrolide treatment – a class of treatments commonly used to treat bacterial infections. Since it is likely that Yaws patients will have taken other macrolides previously for other diseases, they could have developed antibiotic resistance against any macrolide, including azithromycin.10 In these cases, patients can take benzathine penicillin instead.
Although Yaws can be treated with antibiotics at any stage, there is currently no treatment available for the degradation of bones associated with the tertiary phase of Yaws.
Global efforts to eradicate yaws
The World Health Organisation (WHO) is aiming to eradicate Yaws, as the infection can be easily treated and contained as long as outbreaks are properly monitored.2 This would be the third disease (after polio and dracunculiasis (guinea-worm disease)) to be eradicated.
In order to achieve this, WHO have set themselves the following goals:
- Developing strategies to aid countries which have a high incidence of Yaws in implementing eradication activities
- Developing educational material to promote personal hygiene and raise awareness for the disease
- Developing training material for healthcare workers to help identify Yaws within impoverished communities
- Donating 153 million tablets of azithromycin to countries in need
- Creating tools to objectively collect data in order to track Yaws incidence
- Collaborating with stakeholders and partnerships to help achieve their goals
WHO is currently working on implementing a mass-drug administration approach, which would involve treating entire (or at least 90% of) at-risk communities with azithromycin. In 2020, WHO collaborated with the Brazilian pharmaceutical company EMS Group to provide 1.4 million azithromycin tablets to Cameroon. Between 2021 - 2023, another 9 million tablets will be provided to other countries, such as Vanuatu, Central African Republic, Congo, Solomon Islands, and Papua New Guinea.2
Further, research aiming to eradicate Yaws is taking place all around the world. One study in Papua New Guinea was recently undertaken to assess the administration of multiple rounds of azithromycin at 6-month intervals and found that continued treatment helped reduce the chance of Yaws infections recurring.10 Another study is assessing whether the low-cost drug linezolid, which has shown to be effective in treating syphilis, could be used to treat Yaws in patients with azithromycin-resistant infections.2
Yaws is a skin infection caused by the Treponema pallidum subspecies pertenue bacterium, which results in the formation of non-cancerous, itchy lumps and ulcers. If left untreated, Yaws can lead to more severe consequences, such as bone deformity and destruction. Yaws is highly infectious as it is transmitted between humans via skin-to-skin contact, and it occurs mostly in children under the age of 15 in tropical, impoverished countries. Fortunately, there are effective antibiotics that can cure this infection in the majority of patients. However, the disease has no specific diagnostic tool, and there is still no vaccine. Therefore, further research must still be done to help the eradication of this infectious disease.
- Mitjà O, Asiedu K, Mabey D. Yaws. Lancet. 2013 Mar 2;381(9868):763–73.
- Yaws [World Health Organisation]. [cited 2023 Sep 27]. Available from: https://www.who.int/news-room/fact-sheets/detail/yaws
- Yaws - symptoms, causes, treatment [Rare Diseases]. [cited 2023 Sep 27]. Available from: https://rarediseases.org/rare-diseases/yaws/
- González-Beiras C, Vall-Mayans M, González-Escalante Á, McClymont K, Ma L, Mitjà O. Yaws osteoperiostitis treated with single-dose azithromycin. Am J Trop Med Hyg. 2017;96(5):1039–41.
- Treponema pallidum - an overview [ScienceDirect]. [cited 2023 Sep 27]. Available from: https://www.sciencedirect.com/topics/neuroscience/treponema-pallidum
- Wicher K, Wicher V, Abbruscato F, Baughn RE. Treponema pallidum subsp. pertenue Displays Pathogenic Properties Different from Those of T. pallidum subsp. pallidum. Infect Immun. 2000;68(6):3219–25.
- Bejel, pinta, and yaws - infectious diseases [MSD Manual Professional Edition]. [cited 2023 Sep 27]. Available from: https://www.msdmanuals.com/professional/infectious-diseases/spirochetes/bejel,-pinta,-and-yaws
- Md Alwi N, Muhamad R, Ishak A, Wan Abdullah WNH. Yaws: The forgotten tropical skin disease. Malays Fam Physician. 2021 ;16(3):104–7.
- Zhang Y, Goh SM, Mello MB, Baggaley RC, Wi T, Johnson CC, et al. Improved rapid diagnostic tests to detect syphilis and yaws: a systematic review and meta-analysis. Sex Transm Infect. 2022 ;98(8):608–16.
- Kwakye-Maclean C, Agana N, Gyapong J, Nortey P, Adu-Sarkodie Y, Aryee E, et al. A single dose oral azithromycin versus intramuscular benzathine penicillin for the treatment of yaws-a randomized non inferiority trial in ghana. PLoS Negl Trop Dis. 2017 ;11(1):e0005154.