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Can we eradicate yaws?

Yaws, which is also called framboesia, is caused by the bacterium Treponema pallidum subsp. pertenue and classified as a Neglected Tropical Disease by the WHO. The bacterium infects humans and non-human primates. The name framboesia is derived from lesions that resemble raspberries (French: framboise).1

Within 90 days of being infected, patients develop symptoms in the form of lesions which completely disappear again within six months. A second round of lesions erupt months to years later, also healing off again within six months but likely leaving behind scars. In approximately 10% of untreated cases, a third round of lesions can occur and result in complications such as destruction of skin, bones and cartilage. The Oxford Textbook of Medicine describes yaws as “rarely fatal”.2

Yaws is spread by skin-to-skin contact and rarely via objects, by bacteria entering through broken skin. An infection can spread from patients currently suffering from lesions, from people who carry the bacteria but at that moment do not have lesions, as well as from non-human primates.

Yaws was almost eradicated in the early 1960s already but re-emerged due to discontinued support from the WHO and lack of attention by governments’ healthcare systems. It is back on the WHO’s list of diseases to be eradicated by 2020. This is believed feasible because effective antibiotics exist against yaws. The required mass treatments are relatively easy and cheap to administer. However, many countries do not monitor and report yaws cases to the WHO so that the global number of cases and thereby progress towards eradication remains largely unknown.3

Means against the disease

The spread of the Treponema pallidum bacterium can be fought in two ways; improved hygiene and health education as well as antibiotic treatment. While improved hygiene and health education reduce the bacterium’s transmission, antibiotic treatment heals infected people and thereby reduces the number of carriers of the disease.4

Usually, yaws patients were treated with a single dose of penicillin but in 2012 it was discovered that a single, swallowed dose of another antibiotic called azithromycin could completely cure yaws.5

Yaws was usually diagnosed by the emergence of symptoms, i.e. the first round of lesions. Blood tests could confirm the presence of the Treponema pallidum bacterium but could not differentiate between active and past infections. Recently, new diagnostic tests have been developed that can diagnose a yaws infection faster and more accurately.6 This is important as the correct antibiotics could be immediately prescribed to confirmed yaws patients and avoid unnecessary oversubscription of antibiotics to patients suffering from similar symptoms caused by different pathogens.

The road towards yaws eradication

The history of yaws eradication efforts illustrates the importance of political support. Yaws ticks all the required features for disease eradication: it is caused by only one species of bacteria, only infects humans and non-human primates, good and cheap means against and diagnostics for yaws exist and both some countries have successfully interrupted its transmission. The reason why yaws has not been eradicated yet is “simply” that for a long time, yaws has been neglected; no eradication campaigns were run and no records of case numbers were kept. Even today, only eight countries report yaws cases to the WHO.

The disease-causing pathogen of yaws was identified in 1905 but it was not until the establishment of the World Health Organisation in the aftermath of World War II that antibiotics were tested as a treatment option.7

Anecdotal evidence suggests that the disease burden prior to the WHO efforts was extremely high: In what today constitutes Ghana in 1936, 62.7% of all infectious diseases treated in government health facilities were yaws cases (for comparison, malaria only accounted for 20.3%).8

It has been estimated that in 1955, there were 50 million yaws cases worldwide.9 Therefore, after a few pilot projects that tested the efficacy of the antibiotic penicillin, the WHO together with UNICEF launched mass treatment campaigns in 46 countries in 1952. By 1964, after screening approximately 300 million people and administering approximately 50 million penicillin doses to patients and their close contacts, yaws cases were said to be reduced by 95% to just 2.5 million cases. In light of such a successful reduction in yaws’s disease burden, internationally coordinated mass campaigns were discontinued and countries’ primary health care systems were tasked with the elimination of the last 5% of cases. Global interest faded, developing countries’ healthcare systems already had too much on their plate and since no records were kept anymore, nobody knew how yaws numbers were developing.

It was only with a WHO review of its Neglected Tropical Diseases in 2012 that yaws regained international attention. The WHO even declared it its goal of eradicating yaws by 2020.
These renewed eradication efforts make use of a different antibiotic called azithromycin (described in the previous section) that can be administered orally. A new strategy is to give azithromycin to everyone living in a yaws-prone community, regardless of whether they suffer from yaws or not.10

To achieve the eradication of yaws, better monitoring in endemic countries as well as determining the endemicity status of all remaining countries will be necessary. For instance, it is unclear whether the disease is still in circulation in the Americas today.11

The world map visualizes the only data available – a country’s status of endemicity in 2016 and the number of cases for a few countries that reported yaws infections to the WHO. Fourteen countries are known to be endemic, even though for many more countries (all those shown in yellow) it is unknown whether yaws is still in circulation. Thanks to determined mass treatment and monitoring programs, India and Ecuador successfully eliminated yaws and are certified yaws-free by the WHO. They are coloured green in the map. Endemic countries are depicted in red or orange in the map, depending on whether the country reported the number of yaws cases to the WHO in 2016 or not, respectively. When hovering over the countries shown in red the number of cases will appear.