Yaws is a disfiguring, treatable bacterial disease that still affects children in remote, poor communities across the tropics. For decades the only reliable cure required a painful intramuscular injection, delivered village by village, often by health workers stretched thin across difficult terrain. Over the last fifteen years, a large randomized trial and a revised World Health Organization strategy have shifted the standard treatment to a single oral dose of azithromycin. This article explains what yaws is, why the shift happened, what the evidence actually shows, and where real uncertainty remains — including the emergence of drug resistance that has complicated the eradication effort.

What Yaws Is, and Why a Child's Skin Infection Matters

Yaws is caused by Treponema pallidum subspecies pertenue, a spiral-shaped bacterium closely related to the organism that causes syphilis, though yaws is not sexually transmitted. It spreads through direct skin contact, typically among children under fifteen living in poor, rural, tropical communities in West and Central Africa, Southeast Asia, and the Pacific islands. Left untreated, it produces raised, raspberry-like skin lesions that can ulcerate, and in a minority of cases progresses to destructive changes in bone and cartilage, sometimes leaving lasting disfigurement in a child who did nothing to deserve it.

Mass penicillin campaigns in the 1950s and 1960s, coordinated by WHO and UNICEF, treated tens of millions of people and drove global case numbers down dramatically — from an estimated fifty million cases to under three million within about fifteen years. That achievement is a genuine public health success story. But when the campaigns wound down, surveillance lapsed in many places, and the disease crept back in pockets of Papua New Guinea, the Solomon Islands, Indonesia, Ghana, and elsewhere. Every child who has since been born with active, untreated yaws is a reminder that eradication is not a permanent state achieved once — it requires sustained attention, precisely because these are among the poorest, least visible communities on earth.

From Needle to Pill: The Pharmacology Behind the Shift

Benzathine penicillin G, given as a single deep intramuscular injection, has long been curative for yaws and remains effective. But it has real practical drawbacks in mass campaigns: it requires trained personnel to administer safely, carries a small but real risk of injection-site complications and allergic reaction, needs refrigeration in some formulations, and — understandably — many children fear and resist a needle, which undermines the population coverage a mass campaign depends on.

Azithromycin is a macrolide antibiotic, derived originally from erythromycin, itself a product of Saccharopolyspora erythraea, a bacterium first isolated from soil. It works by binding the bacterial ribosome and blocking protein synthesis, halting the organism's ability to replicate. It is already a familiar, well-studied drug, approved in many countries for respiratory infections, certain skin infections, and some sexually transmitted infections — its safety profile in children is well characterized from decades of use. That an antibiotic drawn originally from a humble soil organism should turn out to be exactly suited to reaching children in the world's hardest-to-serve villages, in a form a community health worker can carry in a pocket and give as a single tablet or liquid dose, is the kind of practical fit worth pausing over.

It bears stating plainly: azithromycin's use for yaws is a public health application under WHO guidance and national ministry of health protocols in endemic countries. It is not an FDA-approved indication in the United States, where yaws does not occur, and this article is not advice for treating any individual patient — that decision belongs to a treating physician working within the relevant national program.

The Papua New Guinea Trial That Changed Practice

The pivotal evidence came from a randomized controlled trial conducted on Lihir Island, Papua New Guinea, led by Oriol Mitjà and colleagues and published in The Lancet in 2012. Researchers compared a single oral dose of azithromycin (30 mg per kilogram of body weight, up to a maximum of 2 grams) against the standard single intramuscular injection of benzathine penicillin in children with active yaws lesions. At follow-up, both treatments produced cure rates in the mid-to-high nineties percent range, and the trial met its pre-specified statistical criteria for non-inferiority — meaning azithromycin was not meaningfully worse than penicillin at clearing the infection.

This was a well-designed clinical trial, not a laboratory finding or an animal study, and it was conducted in the exact population the intervention was meant to serve, which strengthens confidence in its relevance. Follow-up work by the same research group, published in subsequent years, tracked what happened when azithromycin was used not just to treat individual patients but to treat an entire endemic community at once — the approach now central to WHO strategy. Those community-level campaigns reported substantial reductions in active yaws prevalence within about a year of a single round of mass treatment, though the precise magnitude varied by location and by how thoroughly the population was covered.

The Morges Strategy: Treat the Whole Village, Then Mop Up

In 2012, WHO convened a technical consultation in Morges, Switzerland, that formally adopted this trial evidence into a new global eradication strategy — now generally referred to as the Morges strategy. It replaced the older approach, which relied on identifying and treating individual cases and their close contacts with penicillin, with a two-phase model built around azithromycin's ease of oral administration:

This model depends on reaching very high coverage in a single pass — WHO guidance has generally aimed for coverage above roughly 90 percent of the eligible population — because incomplete treatment leaves a reservoir of infection that can reseed the community. That is a demanding logistical target in remote settings, and it is worth being honest that achieving it consistently, campaign after campaign, across dozens of countries, remains one of the program's harder practical challenges, distinct from the underlying drug efficacy question.

Resistance and Honest Uncertainties

No responsible account of this program can stop at the good news. Mitjà and colleagues published findings in The Lancet in 2018 documenting the re-emergence of yaws cases in a Papua New Guinea community some years after a mass azithromycin treatment round, and laboratory analysis of the responsible bacteria identified specific mutations in the ribosomal RNA gene target of azithromycin — the same class of mutation known to confer macrolide resistance in other bacteria. This is a genuine, documented finding in humans and isolated organisms, not a theoretical concern, and it means resistance can and does arise under repeated mass treatment pressure, just as it can with any single-drug mass campaign against any organism.

What this means in practice is still being worked out. Resistance has not been reported everywhere azithromycin mass treatment has been used, and penicillin remains fully effective as a backup for documented treatment failures. But it is a legitimate reason WHO's original 2020 target date for global yaws eradication was not met, and the effort has since been folded into WHO's broader 2021–2030 neglected tropical disease roadmap with a longer horizon. Readers should treat "eradication by [date]" claims with the same caution any informed patient brings to any ambitious public health timeline — the biology of drug resistance does not respect deadlines, and ongoing surveillance, not just the initial mass dose, is what will determine whether this strategy holds.

Why a Village Disease Should Matter to Distant Readers

Yaws will never appear on a clinic chart in most of the countries reading this. But the underlying principle is not foreign at all: a disfiguring, entirely curable disease is still active in children today largely because attention and resources wavered once before. That is a case study in the value of sustained stewardship over a one-time fix — and a reminder that every child affected, in a village most of us will never visit, is owed the same seriousness of care as any patient closer to home. For readers and families anywhere, the broader lesson translates directly: understand what a medicine actually does and does not do, ask your own physician plain questions about dosing, resistance, and alternatives, and do not assume that a single dose of anything is a permanent solution rather than one step in ongoing care.