Where the road ends: neglected tropical diseases (NTDs)
The NTDs encompass a range of viral, bacterial and parasitic infections of the poorest communities worldwide.
Whilst traditionally receiving less attention and funding than HIV, malaria and TB (the ‘big three’), there has been renewed global interest in control of NTDs in recent years. This led to the 2012 London Declaration: a landmark collaboration of academics, NGOs, pharmaceutical companies and government representatives, who pledged commitment to the elimination and eradication of specific NTDs by 2020.
Yaws
Yaws is one of the NTDs recognised by the World Health Organization (WHO). Caused by infection with the bacterium Treponema pallidum subsp. pertenue, yaws manifests as chronic and disfiguring lesions of skin, cartilage and bone if untreated. Children are most commonly affected, with infection rates of more than 50% by the age of 15 in some communities. Whilst the bacterium responsible for yaws is almost identical to the causative agent of syphilis, yaws is not sexually transmitted but often spreads between children’s skin as their lower limbs touch (Mitjà O, Asiedu K, Mabey D. Yaws. Lancet 2013; 381: 763-73).
Where is yaws found?
Yaws was found throughout the tropics in the twentieth century. However, since the 1950s mass treatment and improved socioeconomic conditions have reduced its distribution worldwide. Yaws is now only found in West Africa, South-East Asia and the Pacific, with almost 80% of cases (60,000 reports per year) in just three countries: Ghana, Papua New Guinea and the Solomon Islands (DOI: 10.1093/bmb/ldu037).
Eradicating yaws
In 2012, the WHO launched a new campaign for the global eradication of yaws by 2020. Its success rests upon the identification of yaws endemic communities (defined by at least one case), followed by treatment of that whole community with a single oral dose of the antibiotic azithromycin. A study conducted in Papua New Guinea showed azithromycin to be more than 95% effective in treating individuals with yaws. Government led campaigns conducted at the end of the twentieth century successfully eliminated yaws from India and Ecuador, lending hope to renewed efforts towards global eradication.
What must be done?
There is an urgent need for studies to identify yaws endemic communities, so that mass treatment can be appropriately directed. One complicating factor is that some other skin conditions can look like yaws. RSTMH helped to fund a study in Ghana where many children who were thought to have yaws were proven to have a different reason for skin ulceration. The London School of Hygiene and Tropical Medicine, WHO, Centers for Disease Control and Barcelona Institute for Global Health have together shown that simple, field-based point-of-care tests can improve the accuracy of diagnosis. It is hoped that making these tests widely available in yaws endemic countries will facilitate appropriately directed treatment (both initially and during surveillance), until the interruption of transmission can finally be declared.
Skin ulcers not caused by yaws
Whilst many lesions may be non-infective in origin (for example those caused by burns, bites or scratches from vegetation), secondary infection is also possible. Education of communities and addressing other causes of skin disease will be necessary for full engagement with yaws elimination programmes. Another bacterium, Haemophilus ducreyi (H. ducreyi), has also recently been implicated in skin ulcers clinically indistinguishable from yaws. Although normally thought of as being responsible for the sexually transmitted genital ulcer disease chancroid, H. ducreyi has been found in ulcers in Papua New Guinea, the Solomon Islands, Vanuatu and Ghana.
Summary
Eradication of yaws would alleviate the suffering and disability of thousands of children in some of the world’s poorest communities. Additional benefit would be derived if other common causes of ulcerative skin disease in children could be addressed in parallel. The campaign to eradicate yaws has gained pace over the last three years, and pilot trials of the WHO’s mass treatment strategy are ongoing in West Africa and the Pacific. Long term political commitment and allocation of resources are necessary to reduce the overall burden of childhood skin disease and rid the world of yaws.