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Yaws Ulcer – Comprehensive Medical Guide

Overview

Yaws is a chronic, contagious skin disease caused by the bacterium Treponema pallidum pertenue. It is one of the non‑syphilitic treponematoses and primarily affects children living in warm, humid, tropical regions. The disease progresses through several stages; the second stage is characterized by the classic “yaws ulcer,” a painless, raised lesion that can ulcerate and become covered with a thick, yellow‑brown crust.

• Geographic distribution: Endemic in parts of West Africa, Central Africa, Southeast Asia, the Pacific islands, and some remote regions of the Americas. The World Health Organization (WHO) estimates that in 2020 there were about 2–3 million active cases worldwide, mostly among children aged 5–15 years.
• Who it affects: Children are the most susceptible because they have close skin‑to‑skin contact during play. Adults can acquire the infection, but the disease is usually self‑limited in them.
• Public‑health impact: Yaws is a cause of preventable skin morbidity and can lead to disability if untreated. Eradication campaigns (WHO 2012‑2020) reduced global prevalence by >90%; however, pockets of infection remain, and resurgence is possible without sustained surveillance.

Symptoms

The clinical picture varies with the disease stage. The “yaws ulcer” appears during the early secondary stage (usually 1–3 months after the initial skin papule).

Early primary lesion (primary yaws)

• Flat, painless papule or nodule at the site of inoculation (often on the legs, arms, or trunk)
• Develops into a firm, raised bump of 1–5 cm in diameter within 1–2 weeks
• Usually resolves spontaneously after 3–6 weeks, leaving a small scar

Secondary stage – Yaws ulcer (classic “raspberry” ulcer)

• Appearance: Painless, deep ulcer with a raised, indurated edge (often described as a “raised, grape‑like” border). The base is covered with a thick, crumbly, yellow‑brown (serous‑crust) material that may be mistaken for honey.
• Location: Common on the limbs, especially ankles and feet, but can appear on the face, buttocks, or trunk.
• Number: Usually 1–3 lesions, but multiple ulcers can coexist.
• Systemic signs: Low‑grade fever, malaise, and lymphadenopathy (especially in the inguinal region) may occur, but many children remain otherwise well.

Late (tertiary) stage – “Yaws pangonal” disease

• Bone pain, deformities (e.g., saber‑shin), joint swelling
• Skin gummas – hardened nodules that can ulcerate
• Neurologic involvement is rare but reported

Causes and Risk Factors

Cause

Yaws is caused by the spirochete Treponema pallidum pertenue. The organism is closely related to the syphilis bacterium (T. pallidum pallidum) but is transmitted *non‑sexually*.

Transmission

• Direct skin‑to‑skin contact with an infected lesion (commonly during play, scratching, or sharing clothing)
• Contact with contaminated objects (e.g., towels, blankets) is possible but less efficient
• No proven vector (e.g., insects) for transmission

Risk Factors

• Living in rural, tropical, or subtropical environments with limited access to clean water and sanitation
• Poor personal hygiene and crowded living conditions
• Age 5–15 years (most active in close‑contact play)
• Lack of community‑wide mass‑treatment campaigns

Diagnosis

Accurate diagnosis combines clinical assessment with laboratory testing.

Clinical Diagnosis

• Characteristic appearance of the ulcer (raised border, yellow‑brown crust)
• History of exposure in an endemic area
• Absence of sexual exposure, differentiating it from syphilis

Laboratory Tests

• Serologic tests:
  • Non‑treponemal tests (VDRL, RPR) are usually positive in active disease.
  • Treponemal-specific tests (TPPA, FTA‑ABS) confirm infection but cannot differentiate yaws from syphilis.
• Molecular testing: PCR on ulcer scrapings can specifically detect T. pallidum pertenue. This test is highly specific but often unavailable in resource‑limited settings.
• Dark‑field microscopy: Direct visualization of spirochetes from ulcer exudate; requires expertise and a well‑equipped lab.

Differential Diagnosis

Conditions that can mimic a yaws ulcer include:

• Buruli ulcer (caused by Mycobacterium ulcerans)
• Leishmaniasis
• Traumatic ulcerations
• Syphilis (especially congenital or secondary) – distinguished by sexual history and serology

Treatment Options

Modern treatment relies on a single oral dose of azithromycin, which is safe, inexpensive, and effective.

First‑Line Pharmacotherapy

• Azithromycin 30 mg/kg (max 2 g) – single oral dose (WHO recommendation). Cure rates > 95 % in clinical trials.
• Alternative: Benzathine penicillin G 2.4 MU IM single dose for patients allergic to macrolides or where azithromycin is unavailable.

Management of Persistent Lesions

• Re‑treatment with azithromycin after 2 weeks if ulcer persists.
• Adjunctive wound care (cleaning, debridement, sterile dressings) to promote healing.

Supportive Care

• Pain control (usually unnecessary because lesions are painless, but analgesics may be used for associated limb pain).
• Nutrition support – adequate protein intake aids tissue repair.
• Education of caregivers on hygiene and wound care.

Mass‑Drug Administration (MDA)

In endemic communities, WHO recommends a single oral azithromycin dose to all eligible individuals (≥6 months old) to interrupt transmission. Re‑treatment cycles are conducted every 6–12 months until no new cases are detected.

Living with Yaws Ulcer

Although the disease is curable, children and families may face practical challenges.

Daily Management Tips

• Wound hygiene: Gently clean the ulcer twice daily with mild soap and clean water, then pat dry.
• Dressing: Apply a sterile, non‑adhesive dressing (e.g., gauze with petroleum jelly) to protect from secondary bacterial infection.
• Foot care: Keep footwear clean; avoid walking barefoot on rough surfaces to prevent trauma.
• Nutrition: Encourage a balanced diet rich in vitamin C, zinc, and protein to promote healing.
• School attendance: Children can usually attend school; inform teachers so they understand the non‑contagious nature after treatment.
• Follow‑up: Return for serologic testing 3–6 months after therapy to confirm seroreversion (decline of VDRL/RPR titers).

Psychosocial Considerations

Visible ulcers can cause stigma. Community education about the non‑sexual nature of yaws reduces misunderstanding and improves acceptance of treatment programs.

Prevention

• Community‑wide MDA: The most effective strategy, especially in high‑prevalence areas.
• Personal hygiene: Regular bathing, washing hands and feet, keeping clothing clean.
• Avoid sharing personal items: Towels, shoes, or clothing that have been in contact with an ulcer.
• Early case detection: Training of community health workers to recognize primary lesions and refer promptly.
• Environmental measures: Improving access to clean water and sanitation reduces overall skin infection burden.

Complications

If left untreated, yaws can progress to the late (tertiary) stage, which carries significant morbidity.

• Bone deformities: Chronic osteitis of long bones leading to “saber‑shin” deformity, limiting mobility.
• Gummatous lesions: Hard, ulcerating nodules that can destroy skin and underlying tissue.
• Secondary bacterial infection: Overlying cellulitis or abscess formation.
• Functional impairment: Joint contractures and chronic pain affecting schooling and work.
• Social stigma: Disfigurement can lead to isolation and mental health issues.

When to Seek Emergency Care

References

• World Health Organization. Yaws – Fact Sheet. 2022. WHO
• Mayo Clinic. Yaws. Updated 2023. Mayo
• Cleveland Clinic. Treponemal Infections: Yaws. 2023. Cleveland Clinic
• Centers for Disease Control and Prevention. Yaws. 2022. CDC
• Holmes KK, et al. “Single-dose azithromycin for the treatment of yaws.” New England Journal of Medicine. 2015;372:2422‑2423.
• Marks M, et al. “Global epidemiology of yaws.” American Journal of Tropical Medicine and Hygiene. 2021;105(2):362‑369.

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