Epidemiology
Because T. pallidum pertenue is temperature- and humidity-dependent, yaws is found in humid tropical forest regions in South America, Africa, Asia and Oceania.About three quarters of people affected are children under 15 years of age, with the greatest incidence in children 6–10 years old. Therefore, children are the main reservoir of infection.It is more common in remote areas, where access to treatment is poorer. It is associated with poverty and poor sanitation facilities and personal hygiene.Worldwide, almost 85% of yaws cases are in Ghana, Papua New Guinea, and the Solomon Islands. Rates in sub-Saharan Africa are low, but tend to be concentrated in specific populations. As of 2015, it is estimated that about 89 million people live in yaws-endemic areas, but data are poor, and this is likely an over-estimate.In the early 1900s, yaws was very common; in sub-saharan Africa, it was more frequently treated than malaria, sometimes making up more than half of treatments.Mass treatment campaigns in the 1950s reduced the worldwide prevalence from 50 to 150 million to fewer than 2.5 million; however, during the 1970s there were outbreaks in South-East Asia, and there have been continued sporadic cases in South America. As of 2011, it was unclear how many people worldwide were currently infected.From 2008 to 2012, 13 countries reported over 300,000 new cases to the WHO. There was no system for certifying local elimination of yaws, and it is not known whether the lack of reports from some countries is because they stopped having yaws cases or because they stopped reporting them.
Treatment
Treatment is normally by a single intramuscular injection of long-acting benzathine benzylpenicillin, or less commonly by a course of other antibiotics, such as azithromycin or tetracycline tablets. Penicillin has been the front-line treatment since at least the 1960s, but there is no solid evidence of the evolution of penicillin resistance in yaws.The historical strategy for the eradication of yaws (1952–1964) was:
Benzathine benzylpenicillin requires a cold chain and staff who can inject it, and there is a small risk of anaphylaxis. It was also not reliably available during the 2010s; there have been supply shortages.In the 2010s, a single oral dose of azithromycin was shown to be as effective as intramuscular penicillin. Unlike penicillin, there is strong evidence that yaws is evolving antibiotic resistance to azithromycin; there are two known mutations in the bacterium, each of which can cause resistance and make the treatment ineffective. This has threatened eradication efforts.Within 8–10 hours of penicillin treatment, bacteria can no longer be found in lesion biopsies. Primary and secondary lesions usually heal in 2–4 weeks; bone pain may improve within two days. If treated early enough, bone deformities may reverse and heal. Primary and secondary stage lesions may heal completely, but the destructive changes of tertiary yaws are largely irreversible.If lesions do not heal, or RPR test results do not improve, this may indicate treatment failure or re-infection; the treatment is typically repeated. WHO guidelines says that any presumed treatment failures at 4 weeks require macrolide resistance testing.