Yaws is a skin neglected tropical disease (NTD) targeted for eradication.
It is a chronic, disfiguring and debilitating infectious disease which affects mainly the skin, but can also involve the bone and cartilage. Early detection and treatment can avoid gross disfigurement and disability which occur in about 10% of cases.
Yaws is caused by infection with a spiral bacterium called Treponema pallidum subspecies pertenue, which is closely related genetically to T. pallidum subspecies pallidum, the causative agent of syphilis and the causative bacteria of other endemic non venereal trepanomatoses (bejel and pinta).
Yaws is transmitted through direct non sexual contact (from person to person) with fluid from untreated early infectious lesions (papillomas and ulcerations). Although the lesions may heal spontaneously, some lesions may recur.
Humans, specially children, are currently believed to be the only reservoir.
The incubation period is between 9 and 90 days, with an average period of 21 days.
The clinical manifestations of untreated disease present in the following stages:
- Primary stage: a single papule forms at the organisms´site of entry after the incubation period. The papule may develop into a papilloma which grows gradually. The papilloma is a typical presentation of yaws and clinical diagnosis is straightforward. In 65-85% of cases, the primary lesions of yaws are seen on the legs and ankles. Without treatment, the papilloma will ulcerate. The diagnosis of the ulcerative form is more challenging and requires serological confirmation. Papilloma and ulcers are very infectious and in the absence of treatment can quickly spread to others.
- Secondary stage: it occurs weeks to months after the primary infection if left untreated with antibiotics and due to the spread of the causative organisms to the blood and lymph. More generalized and multiple lesions may appear on the face, neck, armpits, arms, leggs and buttocks or pain and swelling of long bones and fingers (dactylitis).
- Latent yaws: If left untreated, the infectious lesions of primary and secondary yaws will heal spontaneously and the disease may enter a period of latency with no physical signs. Latent yaws can only be detected as a result of serological testing.
- Tertiary stage: Although spontaneous healing may occur in many cases, a minority may progress from latency to the tertiary stage. This destructive, non-infectious stage of the disease is characterized by gumma formation and may appear after a variable period of latency. Although rarely fatal, this stage affects the bones, joints and soft tissues, and frequently leads to deformities of the skin, cartilage and bone. Such cases may develop severe and chronic disfigurement of the face and legs and disability resulting in stigma, social exclusion, school absenteeism and restricted participation in the community.
Ulcers caused by Haemophilus ducreyi is an important cause of skin ulcers (mostly on the legs) which clinically mimic the ulcerative form of yaws could complicate clinical diagnosis. About 40% of ulcers clinically identified as yaws are caused by H. ducreyi.
All individuals with suspected yaws lesions should be examined by trained health workers. A clinical diagnosis should be established based on the patient’s history, endemicity of yaws in the area and characteristics of the lesions. Based on the clinical findings, the individual will be classified as suspected yaws case or non-yaws case.
For serological confirmation, traditionally, laboratory-based methods such as Treponema pallidum particle agglutination assay (TPPA) or Treponema pallidum haemagglutination assay (TPHA) and rapid plasma reagin (RPR) are widely used to diagnose treponemal infections (for example, syphilis and yaws). These tests cannot distinguish yaws from syphilis, however, and the interpretation of results from these tests in adults who live in yaws endemic areas therefore needs careful clinical assessment.
Rapid treponemal point-of-care (POC) tests are widely available and used in the field. However, most of them are treponemal-based and cannot distinguish between past and current infection and therefore has a limited use in monitoring interruption of transmission. The dual path platform (DPP) can detect both past and present infection. This simplifies diagnosis in the field and can also be used to monitor interruption of transmission.
Polymerase chain reaction (PCR) technology is used to definitively confirm yaws by detecting the organisms’ DNA in the skin lesions. It can also be used to monitor azithromycin resistance. The application of PCR in yaws eradication will be very useful after mass treatment and post-elimination surveillance when the few cases that occur must be proven to be yaws.
Since 2012, yaws can be cured with a single oral dose of an inexpensive antibiotic (30 mg/kg body weight, maximum 2 g) called azithromycin as an alternative to benzathine penicillin injection (single intramuscular dose). This last one can be used for patients with suspected clinical treatment failure after azithromycin, or patients who cannot be treated with azithromycin (0.6 million units in children aged under 10 years and 1.2 million units in people aged over 10 years).
The efficacy of oral azithromycin in mass treatment has been tested through pilot programmes in 5 countries since 2012. All tests have demostrated excellent results with complete cure achieved within 2-3 weeks of a patient taking the required dose of the antibiotic.
Patients should be reexamined 4 weeks after antibiotic treatment – in over 95% of cases, complete clinical healing will be observed. Any individual with presumed treatment failure requires macrolide resistance testing.
There is no vaccine for yaws. Health education and improvement in personal hygiene are essential components to reduce transmission of the disease. Contacts of patients with yaws should receive empiric treatment. Prevention is based on the interruption of transmission by (targeted) mass drug treatment of communities and early diagnosis.
About 75– 80% of people affected are children under 15 years of age. Peak incidence occurs in children aged 6–10 years, and males and females are equally affected.
The disease is found primarily in poor communities in warm, humid and tropical forest areas of Africa, South-East Asia, Latin America and Western Pacific. The majority of affected populations, mostly children, live at the “end of the road”, far from health services and difficult-to-access areas. In these areas, poverty, low socio-economic conditions and poor personal hygiene facilitate the spread of yaws.
Since 1990, reporting of yaws to WHO is not mandatory and therefore the data availability may be limited. Only 14 out of the 90 countries and territories have recent data on yaws based on the routine surveillance system; however, these figures may just be an indication of the presence of the disease and not its full extent. Ghana, Papua New Guinea and the Solomon Islands report over 10 000 cases per year. In 2017, Philippines confirmed some cases. India is the first country officially declared free of yaws by WHO in 2016.
Which of the cross-cutting issues are relevant
WASH and Wound management
Water, sanitation and hygiene (WASH) are critical in the prevention and care for yaws and NTDs in general. Provision of safe water, sanitation and hygiene is one of the five key interventions within the global NTD roadmap.
Overcrowding, poor personal hygiene and poor sanitation facilitate spread of yaws. Health promotion and improvement in personal hygiene are essential and require access to water. Additionally, clean water and hygiene at health facilities and homes are essential for wound management.
Relevant tools and/or interventions 
Thanks to the new oral treatment, in 2012 WHO convened a meeting of experts to develop a new eradication strategy of yaws, also called The Morges Strategy, which provides two simplified treatment policies:
- Total community treatment (TCT): mass treatment of an entire endemic community, irrespective of the number of active clinical cases, covering at least 90% of the entire population in order to accelerate the interruption of yaws transmission.
- Total targeted treatment (TTT): treatment of all active clinical cases and their contacts (household, school, and playmates).