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Yaws (Chronic Skin Ulcer)

What is Yaws (chronic skin ulcer)?

Yaws is a chronic, contagious skin disease caused by the bacterium Treponema pallidum pertenue. It primarily affects children living in warm, humid, tropical regions, especially in parts of Africa, Asia, the Pacific Islands and Latin America. The disease progresses through distinct stages. In the early (primary) stage, a painless, raised “mother‑crown” papule appears at the site of bacterial entry. If untreated, the infection can evolve into secondary lesions—large, ulcerative, often destructive skin sores that may persist for years, leading to scarring, deformities and disability. Though yaws is not sexually transmitted, its causative organism is closely related to the syphilis spirochete, and the clinical presentation can mimic other treponemal infections.

According to the World Health Organization (WHO), yaws remains endemic in at least 13 countries, with an estimated 84,000 new cases reported in 2022. Because the disease largely affects remote, low‑resource communities, it is often under‑diagnosed, and many individuals live with chronic ulcerative lesions for months or years.

Common Causes

While yaws itself is caused by a specific bacterium, chronic skin ulcers can result from a variety of infectious, inflammatory, vascular, and traumatic conditions. Understanding the differential diagnosis helps clinicians choose the right test and treatment.

• Treponema pallidum pertenue infection (Yaws) – the primary cause of chronic ulcerative skin disease in endemic regions.
• Syphilis (Treponema pallidum pallidum) – congenital or acquired syphilis can produce similar ulcerative lesions.
• Mycobacterium ulcerans infection (Buruli ulcer) – a necrotizing skin infection common near slow‑moving water.
• Leishmaniasis (cutaneous) – protozoan infection causing painless ulcers, prevalent in parts of the Old World.
• Chromoblastomycosis & other deep fungal infections – chronic, warty lesions that may ulcerate.
• Chronic venous insufficiency – venous stasis ulcers on the lower legs.
• Diabetic foot ulcers – neuropathic or ischemic lesions in persons with diabetes mellitus.
• Pressure (decubitus) ulcers – develop over bony prominences in immobile patients.
• Autoimmune blistering diseases (e.g., pemphigoid, pemphigus vulgaris) – can leave chronic erosions.
• Malignancy (Marjolin ulcer) – squamous cell carcinoma arising in long‑standing scars or burns.

Associated Symptoms

Yaws lesions are often painless, which can delay recognition. However, other signs may accompany the ulcers or appear at different disease stages:

• Fever, malaise, and lymphadenopathy during the primary stage.
• Multiple skin papules or nodules that may become ulcerated (“raspberry‑like” appearance).
• Hyperkeratotic or “wart‑like” plaques, especially on the palms and soles.
• Joint pain (arthralgia) and swelling without obvious infection.
• Bone involvement (osteitis) in late disease, leading to pain and deformities.
• Scarring, gummatous tissue, or tissue loss that can impair function, particularly on the legs and hands.
• Secondary bacterial infection of the ulcer (redness, increased pain, purulent drainage).

When to See a Doctor

Prompt medical evaluation is essential to prevent complications and to stop transmission. Seek care if you notice:

• A persistent skin sore that has not healed within 2–3 weeks.
• Multiple lesions, especially on the legs, feet, or face, in a child or adolescent living in or having traveled to an endemic area.
• Any ulcer accompanied by fever, swelling of nearby lymph nodes, or sudden increase in size.
• Signs of secondary infection: increased pain, warmth, redness, pus, or foul odor.
• Development of scar tissue that limits joint movement or causes deformity.
• Any ulcer in a person with diabetes, peripheral vascular disease, or immune compromise.

Early treatment with a single dose of oral azithromycin (or benzathine penicillin where azithromycin is unavailable) can cure the infection and halt disease progression.

Diagnosis

Diagnosing yaws involves a combination of clinical assessment, laboratory testing, and occasionally imaging.

Clinical Evaluation

• Detailed travel and exposure history (living in or recent contact with people from endemic regions).
• Physical examination of lesions: raised papules, ulcerated “mother‑crown” lesions, and characteristic distribution on moist skin surfaces.
• Screening for other treponemal diseases (syphilis) especially in sexually active adults.

Laboratory Tests

• Serologic tests: Rapid plasma reagin (RPR) or Venereal Disease Research Laboratory (VDRL) test may be non‑reactive early; treponemal-specific tests (TPPA, FTA‑ABS) become positive later.
• Polymerase Chain Reaction (PCR): Detects T. pallidum pertenue DNA from ulcer swabs – highly specific and increasingly used in research settings.
• Dark‑field microscopy: Direct visualization of spirochetes from lesion exudate; requires skilled personnel.
• Rapid diagnostic tests (RDTs): Lateral flow assays for treponemal antibodies are field‑friendly and endorsed by WHO for yaws surveys.

Additional Investigations (if needed)

• Complete blood count and inflammatory markers (to assess secondary infection).
• X‑ray or MRI of affected bones if osteitis is suspected.
• Culture for bacterial superinfection when purulent drainage is present.

Treatment Options

Therapeutic goals are to eradicate the treponeme, promote ulcer healing, prevent complications, and interrupt transmission.

Antibiotic Therapy

• Azithromycin 30 mg/kg (max 2 g) orally, single dose – WHO‑recommended first‑line therapy. It is safe for children, pregnant women, and patients with penicillin allergy.
• Benzathine penicillin G 50,000 IU/kg IM (max 2.4 million IU) single dose – alternative where azithromycin resistance or supply issues arise.
• For refractory or late-stage disease, a repeat dose after 2–4 weeks may be required, especially if lesions persist.

Management of Ulcer Healing

• Wound care: Gentle cleaning with saline, debridement of necrotic tissue, and application of non‑adhesive dressings (hydrocolloid or silicone). Change dressings daily or as needed.
• Topical agents: Antimicrobial ointments (e.g., mupirocin) if secondary bacterial infection is suspected.
• Analgesia: NSAIDs for pain or inflammation, unless contraindicated.
• Nutrition: Adequate protein, vitamin C, zinc, and caloric intake to support tissue repair.

Special Situations

• Pregnancy: Azithromycin is preferred; penicillin is safe but requires monitoring for hypersensitivity.
• Immunocompromised hosts: Consider longer courses and close follow‑up because of higher risk of treatment failure.
• Community eradication programs: Mass‑drug administration (MDA) with azithromycin to entire at‑risk populations has shown >95 % reduction in prevalence (WHO, 2023).

Prevention Tips

Because yaws spreads through direct skin‑to‑skin contact with infectious lesions, public‑health measures focus on hygiene, education, and early treatment.

• Teach children to cover open sores with clean bandages and avoid touching or sharing personal items (clothing, towels) with others who have lesions.
• Promote regular skin inspections in endemic schools and community health centers.
• Implement community‑wide azithromycin MDA where yaws prevalence exceeds 5 % (WHO recommendation).
• Encourage timely treatment of any skin ulcer, even if the cause is uncertain.
• Improve access to clean water and sanitation to reduce secondary bacterial infections that can obscure the diagnosis.
• Vaccination research is ongoing; currently no vaccine exists, so surveillance remains essential.

Emergency Warning Signs

Key Take‑aways

Yaws is a treatable bacterial infection that, if left unmanaged, leads to chronic ulcerative skin disease and potential disability. Early recognition—especially in children from endemic regions—combined with a single‑dose oral azithromycin can cure the infection and halt transmission. Proper wound care, nutritional support, and community‑level prevention strategies are essential to reduce the disease burden. Whenever an ulcer fails to heal, shows signs of infection, or is accompanied by systemic symptoms, prompt medical evaluation is critical.

References:

• World Health Organization. Yaws Fact Sheet. 2023.
• Mayo Clinic. Yaws: Symptoms & Causes. Accessed June 2026.
• Centers for Disease Control and Prevention. Treponemal Diseases – Yaws. 2022.
• Cleveland Clinic. Yaws. Reviewed 2025.
• Mitjà O, et al. “Mass Azithromycin Distribution for Yaws Eradication: A Systematic Review.” Lancet Infectious Diseases. 2024;24(5):456‑465.
• National Institutes of Health. Treponema pallidum pertenue Pathogenesis and Control Strategies. 2023.

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