Global Strategy to Eradicate Yaws by 2030 Hinges on Serosurveys, WHO Declares

The World Health Organization has published a new manual that could shape the future of yaws eradication, a neglected tropical disease that scars the skin and bones of children in tropical climates. The guidance was crafted by an informal WHO working group with expertise drawn from leading research institutions such as the Centre for Neglected Tropical Diseases Research at the University of Health and Allied Sciences in Ghana, the Fight Infectious Diseases Foundation in Spain, the London School of Hygiene & Tropical Medicine in the United Kingdom, Lancaster University, Emory University in the United States, and the Universidad Internacional del Ecuador. Working closely with the WHO’s Global Neglected Tropical Diseases Programme, these institutes created a roadmap for national health programmes to use serological surveys to confirm when transmission has been stopped.

The Rigorous Path to Zero Transmission

The guidance stresses that eradication requires patience, precision, and persistence. At least three consecutive serosurveys must be carried out among children aged one to five years, beginning no sooner than two years after the last locally acquired case. Each survey must show less than one percent seroprevalence of treponemal antibodies in this youngest group. The reasoning is that children born after the interruption date should never have been exposed to infection if transmission has truly ended. Yet demonstrating a negative is notoriously difficult. A single survey is not sufficient proof. Instead, repeated surveys over the years, combined with active and passive surveillance systems, provide the confidence needed to declare transmission interrupted.

The manual outlines the sequence of interventions. Mass drug administration with antibiotics, delivered through total community treatment and total targeted treatment, forms the foundation, as established in the 2012 Morges Strategy. If coverage surpasses ninety percent, the disease should be eliminated locally, but because treatment does not confer immunity, reinfection remains possible. Once two years have passed without any indigenous cases, countries may declare “zero cases,” though surveillance must continue vigilantly to prevent reintroduction or hidden persistence.

Designing Surveys That Leave Nothing to Chance

The technical heart of the document lies in survey design. Countries must define evaluation units, geographical blocks where elimination status is assessed, ideally at the district or sub-district level, with populations under half a million. In areas of intense past transmission, smaller units may be required to capture residual risk. Sampling strategies vary from testing every primary unit, such as every village, to cluster sampling weighted by population size. The numbers involved are substantial: thousands of children may need to be tested to ensure statistical certainty.

Serological testing itself brings challenges. No available assay can distinguish yaws from syphilis, so sequential testing is advised, starting with treponemal rapid tests followed by non-treponemal assays like the rapid plasma reagin test. Rapid platforms are quick and suitable for fieldwork, though expensive, while laboratory tests offer slightly better performance. Bead-based immunoassays, though largely confined to reference labs, enable integration with multiple disease surveys. Interpreting the results requires judgment. A high-titre result in a young child after the supposed end of transmission strongly suggests ongoing infection and must trigger treatment, intensified local sampling, and community searches. A low-titre result in older children may simply reflect serofast status, where antibodies persist after successful treatment. Where possible, polymerase chain reaction tests of lesion swabs provide decisive confirmation.

Confronting False Positives and Hidden Hotspots

As prevalence falls, the danger of false positives grows. Even highly specific tests can generate misleading results when almost all those tested are truly negative. The WHO guidance warns against jumping to conclusions and encourages careful follow-up of every positive case. Model-based geostatistics are championed as a powerful tool, harnessing spatial correlation to predict prevalence in unsampled areas and refine future survey design. An example from the Solomon Islands showed infections clustering along coastlines, proving that geographically informed approaches are critical.

Follow-up surveys are indispensable. At least two must be conducted after the initial baseline to confirm that the prevalence remains under one percent and that no resurgence has occurred. If any survey indicates a higher prevalence, countries are urged to extend surveillance by two more years and consider renewed antibiotic campaigns. The bar is intentionally high: eradication demands proof that transmission has not merely paused but has truly ended.

A Cautious but Hopeful Blueprint for Eradication

The manual acknowledges its limitations. Many recommendations rest more on expert consensus than on robust data, but waiting for perfect evidence would paralyze progress. Instead, WHO encourages ministries of health to adapt the guidance to local realities, err on the side of larger sample sizes, and integrate yaws surveillance with other disease programmes whenever possible. Annexes provide practical resources, including ready-to-use code in R and Stata for analysing survey data, while transparency is ensured through disclosure of potential conflicts of interest, none deemed significant.

The broader message is one of cautious optimism. Political commitment, sustainable financing, well-trained health workers, and strong community engagement will be vital. Awareness campaigns, mobile technology, and integration with wider neglected tropical disease strategies can help maintain vigilance during the long surveillance phase. Ultimately, yaws eradication will not be achieved by laboratories and algorithms alone but through collaboration between governments, international partners, researchers, and the communities most affected.

The WHO manual is more than a technical document; it is a call to action. It insists that yaws can be beaten if surveillance is relentless, treatment is widespread, and evidence is built patiently over time. If countries follow this path, the world could witness the first eradication of a bacterial disease, echoing the triumph of smallpox eradication and proving once again that determined global health action can achieve the seemingly impossible.