Yaws
Key facts
- Yaws is a neglected tropical disease of the skin caused by a bacterium.
- Mass treatment campaigns in the 1950s-1960s in 46 countries reduced the prevalence by 95%.
- Yaws still occurs in poor communities in some countries.
- The majority of those affected are children below 15 years of age.
- A single injection benzathine penicillin or azithromycin can cure the disease.
- Yaws can be eliminated and eventually eradicated because humans are the only source of infection.
Yaws is a neglected tropical disease of the skin caused by a treponema bacterium. It is a chronic, non-fatal infection caused by T. Pallidum subspecies pertunue. The disease is also known as framboesia or pian. It is found primarily in poor communities in warm, humid, tropical areas of Africa, Asia, Latin America and the Western Pacific.
Yaws is transmitted mainly through direct skin contact with an infected person. About 75% of people affected are children under 15 years old (peak incidence occurs in children aged 6–10 years). Males and females are equally affected. Overcrowding, poor personal hygiene and poor sanitation facilitate the spread of the disease. Without treatment infection can lead to chronic disfigurement and disability.
Scope of the problem
Since 1990, formal reporting of yaws to WHO stopped due to the discontinuation of yaws programmes in many countries. The last estimate by WHO in 1995 recorded a global prevalence of 2.5 million cases of endemic treponematoses (mostly yaws), including 460 000 infectious cases.
The global prevalence today is unknown. Only a few countries have kept yaws as part of their health programme but possibly some of the 46 previously endemic countries may still harbour the disease.
Data available from six countries are as follows: Cameroon (167 cases; year 2010); Congo (646 cases; year 2009); DRC (383 cases; year 2005); Ghana (20 525 cases; year 2010); Indonesia (6 031 cases; year 2010) and Papua New Guinea (23 000 cases; year 2008). However, these figures may only reflect the tip of the iceberg due to patchy reporting.
List of known endemic countries for yaws in 2011
| Region | Number of countries | Endemic country |
| Africa | 8 | Benin, Cameroon, Central African Republic, Congo, Democratic Republic of the Congo, Côte d’Ivoire, Ghana and Togo |
| Americas | 0 | Last report was on the elimination of yaws from Ecuador in 2003 (1) |
| South-East Asia | 2 | Indonesia and Timor Leste. (note: the last reported cases from India was in 2003) |
| Eastern Mediterranean | 0 | Unknown |
| Pacific | 3 | Papua New Guinea, Solomon Islands and Vanuatu |
Signs and symptoms
There are two basic stages of yaws disease - early (infectious) and late (non-infectious).
- In early yaws, an initial papule (a circular, solid elevation of skin with no visible fluid) develops at the site of entry of the causative organism. This papule is full of the organisms and may persist for 3-6 months followed by natural healing. Without treatment, this is followed by disseminated skin lesions over the body. Bone pain and bone lesions may also occur.
- Late yaws appears five years after the initial infection and is characterized by disfigurement of the nose and bones, and palmar/plantar hyperkeratosis (thickening of the skin on the palms and the soles of the feet).
In the field, diagnosis is primarily based on clinical and epidemiological findings. A person (75% are children below 15 years) who lives in an endemic area is assumed to have yaws if he presents with:
- painless ulcer with scab
- papillomas (benign tumor on skin tissue)
- palmar/plantar hyperkeratosis.
The clinical diagnosis can be confirmed by examining a sample from a skin lesion under a special type of microscope (darkfield examination). This method is impractical in the field and rarely used. Today, laboratory tests such as Rapid plasma reagin (RPR) test, or rapid serological treponemal tests, though not specific for yaws, are simple, rapid, inexpensive and useful for guiding the confirmation of cases. Their interpretation, however, requires a careful evaluation of the clinical and epidemiological context of the cases.
Complications
Without treatment, about 10% of affected individuals develop disfiguring and disabling complications after five years because the disease may cause gross destruction of the skin and bones. It can also cause deformities of the legs, nose, palate and upper jaw.
Treatment
Two antibiotics may be used to treat yaws.
- The standard treatment for yaws is a single intramuscular injection of benzathine penicillin. The dose for adults is 1.2 million units and for children 600 000 units.
or
- A recent study has shown that a single oral dose of azithromycin is as effective as benzathine penicillin (2). The dose is 30mg/kg (maximum 2g).
Prevention
There is no vaccine to prevent yaws. Prevention is based on the interruption of transmission through early diagnosis and mass or targeted treatment of affected population or community. Health education and personal hygiene are essential components of the preventive efforts.
Past effort to eradicate yaws
- Between 1950 and 1970, WHO and UNICEF led a worldwide campaign to control yaws in 46 countries.
- Mass campaigns using mobile teams in all 46 countries led to the treatment of 50 million people and by 1970, the prevalence of the disease had decreased by 95%.
- By the late 1970s, the disease had begun to creep back, resulting in a World Health Assembly Resolution (WHA 31.58) in 1978.
New elimination strategy
The goal and objectives
WHO aims to eliminate yaws from specific geographical areas. The objective is to completely interrupt the transmission of yaws through the mass administration of the recommended antibiotics and eventually eradicate the disease globally by 2020.
Strategy for elimination
The strategy for the elimination of yaws includes:
- identification of the population at risk of infection;
- mass treatment of the entire at-risk population;
- treatment coverage of at least 90% of the at-risk population;
- repeat treatment at 6-monthly intervals until no new cases are recorded in the community;
- registration of all people treated;
- mapping of distribution of cases over time;
- training of health workers and village volunteers.
The prospect of eliminating and eventually eradicating yaws has improved with the advent of a single-dose of oral azithromycin in mass drug administration campaigns. Given the fact that infected humans are the only source of disease, the elimination and eventual eradication of yaws can be achieved within a very relatively short time.
Conditions necessary for yaws elimination
The following conditions may necessary for yaws elimination:
- complete epidemiological information on where cases occur;
- complete access to the entire population at risk;
- national and local political, and community support;
- support from financial partners, private sector and drug donation.
Criteria for elimination
- The clinical criteria will be based on the absence of any report of the disease for three consecutive years after the last reported case, supported by excellent coverage of active surveillance and information, education and communications activities.
- If transmission is interrupted, continuous negative serological tests in children under five, or alternatively negative non-treponemal tests in those under 15, will confirm no further exposure to the infection.
WHO’s response
Yaws has been on WHO’s agenda since its establishment in 1948. WHO provides technical guidance, coordinates elimination efforts and advocates for yaws elimination. Renewed interest in elimination of selected neglected tropical diseases (NTDs) provides an opportunity to eliminate and eventually eradicate yaws.
References
1. Anselmi M. et al. Community participation eliminates yaws in Ecuador. Tropical Medicine and International Health, 2003, 8(7):634–8.
2. Mitjà, O. et al. Single-dose azithromycin versus benzathine benzylpenicillin for treatment of yaws in children in Papua New Guinea: an open-label, non-inferiority, randomised trial, Lancet, 2011, 379, 9813:342-347.