Yaws (Chronic Tropical Skin Infection)

What is Yaws (chronic tropical skin infection)?

Yaws is a contagious bacterial infection of the skin, bone and cartilage that occurs primarily in warm, humid, tropical regions. It is caused by the spirochete Trepobits pallidum subspecies pertenue, a close relative of the bacterium that causes syphilis. Unlike venereal syphilis, yaws is transmitted through direct skin‑to‑skin contact with the fluid from an infectious lesion, not through sexual activity.

After an initial outbreak of painless, raised skin lesions (called “primary yaws”), the disease may become chronic, with recurring nodules, ulcerations and sometimes destructive lesions of the bones. If left untreated, yaws can lead to serious disfigurement, joint deformities, and functional impairment, but it is rarely fatal.

According to the World Health Organization (WHO), yaws remains endemic in at least 13 countries across Africa, Asia and the Pacific, affecting an estimated 2–3 million people, most of whom are children under 15 years of age.¹

Common Causes

Yaws itself is a disease entity, but the appearance of its skin lesions can be confused with other conditions. Below are eight to ten infectious or inflammatory processes that can present similarly and should be considered in the differential diagnosis:

• Treponema pallidum pertenue infection (true yaws) – the classic cause.
• Syphilis (Treponema pallidum pallidum) – venereal form; lesions may look similar but are sexually transmitted.
• Haemophilus ducreyi – causes chancroid, can mimic yaws ulcers in some tropical settings.
• Mycobacterium ulcerans (Buruli ulcer) – produces necrotic skin ulcers, often in the same regions.
• Leprosy (Mycobacterium leprae) – can cause nodular skin lesions and neuropathy.
• Lymphatic filariasis – leads to swelling and skin changes that may be mistaken for late‑stage yaws.
• Cutaneous leishmaniasis – ulcerating lesions after sand‑fly bites, common in some yaws‑endemic areas.
• Scabies with secondary bacterial infection – can produce crusted lesions that look like yaws nodules.
• Chromoblastomycosis – chronic fungal infection producing warty plaques.
• Vitiligo or psoriasis – non‑infectious skin disorders that can coexist and confuse the clinical picture.

Associated Symptoms

The clinical picture of yaws evolves through three stages. The most common associated symptoms are listed below:

• Primary stage (3‑12 weeks after exposure)
  • Single or multiple painless, raised papules or nodules (often on the legs, feet, or arms).
  • Lesions may become ulcerated, forming a “granuloma” with a raised edge and a flat, serous base.
  • Low‑grade fever and mild malaise in some children.
• Secondary (or disseminated) stage (months to years)
  • Rhinopharyngitis‑like symptoms: sore throat, swollen lymph nodes.
  • Multiple smaller skin lesions (macules, papules or nodules) that may ulcerate.
  • Hyperpigmented “gummatous” scars after lesions heal.
• Late (chronic) stage (years after infection)
  • Bone pain and swelling, especially at the tibia, radius or ulna.
  • Joint deformities (e.g., “claw hand”) due to osteitis.
  • Severe disfiguring scarring, especially on the face and limbs.

Because the disease is non‑painful in its early stages, many children continue normal activities, facilitating spread.

When to See a Doctor

Prompt evaluation is important to prevent chronic complications. Seek medical care if you notice any of the following:

• New, painless skin bumps or ulcers that do not heal within 2 weeks.
• Multiple skin lesions appearing after the first one, especially on the limbs.
• Swollen or tender lymph nodes near a skin lesion.
• Persistent fever, night sweats, or unexplained weight loss accompanied by skin changes.
• Bone pain, swelling, or difficulty moving a joint.
• Any skin lesion that begins to bleed, discharge pus, or rapidly enlarges.

Children living in or traveling to known yaws‑endemic areas should be examined by a health professional even if lesions appear mild.

Diagnosis

Accurate diagnosis combines a careful history, physical exam, and selected laboratory tests.

Clinical Evaluation

• Inspection of lesion morphology (raised, ulcerated, “serpiginous” edges).
• Assessment of lesion distribution (typically lower limbs, ankles, sometimes face).
• Documentation of epidemiologic risk (living in endemic rural communities, close contact with infected children).

Laboratory Tests

• Serologic testing – non‑treponemal tests (RPR, VDRL) are usually positive in active disease; treponemal tests (TPPA, FTA‑ABS) confirm exposure.
• Dark‑field microscopy – direct visualization of spirochetes from lesion exudate; requires expertise and is rarely available in remote settings.
• Polymerase chain reaction (PCR) – highly specific for T. pallidum pertenue; becoming more accessible through regional reference labs.
• Bone X‑ray or MRI – indicated when chronic osteitis is suspected; may show periosteal reaction or cortical thinning.
• Skin biopsy – reserved for atypical lesions; histology shows granulomatous inflammation with plasma cells.

World Health Organization (WHO) Simplified Algorithm

In low‑resource settings, WHO recommends a “clinical + serology” algorithm: if a typical lesion is present and either a rapid point‑of‑care treponemal test or a standard RPR is positive, treatment is started without waiting for confirmatory tests.²

Treatment Options

Yaws is highly curable with a single dose of oral azithromycin. Historically, injectable benzathine penicillin was the standard, but azithromycin offers easier administration and better compliance, especially in mass‑treatment campaigns.

First‑Line Antibiotic Therapy

• Azithromycin 30 mg/kg (max 2 g) PO, single dose – recommended by WHO for both individual cases and community‑wide eradication efforts.³
• Alternative for penicillin‑allergic patients: Doxycycline 100 mg PO twice daily for 14 days (not for children <8 years or pregnant women).

When Injectable Penicillin Is Required

• Benzathine penicillin G 1.2 million units IM for adults; pediatric dose is 50,000 IU/kg (max 2.4 million IU).
• Used when azithromycin is unavailable or in cases of treatment failure.

Management of Complications

• Bone involvement – may need prolonged oral antibiotics (e.g., amoxicillin 500 mg TID for 4‑6 weeks) plus orthopedic follow‑up.
• Severe ulcerations – wound care with saline irrigation, sterile dressings, and topical antimicrobial agents (e.g., mupirocin) to prevent secondary infection.
• Pain & inflammation – NSAIDs (ibuprofen 400 mg PO q6‑8 h) as needed.

Home Care and Supportive Measures

• Keep lesions clean and covered to reduce transmission.
• Avoid scratching; use gentle soap and water for daily cleansing.
• Maintain good nutrition and hydration to support immune recovery.
• Educate family members about the non‑sexual transmission route.

Prevention Tips

Because yaws spreads through direct skin contact, community‑level interventions are essential.

• Mass drug administration (MDA) – WHO recommends periodic azithromycin MDA in endemic villages to interrupt transmission.
• Early case detection – train community health workers to recognize primary lesions and refer promptly.
• Personal hygiene – wash hands and feet regularly; keep any skin breaks covered.
• Environmental measures – avoid walking barefoot in dusty or muddy areas; wear closed shoes when possible.
• Education – teach children not to share towels, clothes, or bedding with anyone who has active lesions.
• Vaccination research – a candidate vaccine is under investigation; updates are pending (2024 trials).

Emergency Warning Signs

Key Take‑Away Points

• Yaws is a curable bacterial skin infection prevalent in tropical, low‑resource settings.
• Early recognition of the characteristic painless skin lesions prevents chronic disability.
• A single dose of oral azithromycin is the WHO‑recommended treatment and is highly effective.
• Mass treatment and community education are the most successful strategies for eradication.
• Emergency signs such as severe systemic symptoms or rapid ulcer progression warrant urgent care.

References

1. World Health Organization. Yaws – Fact Sheet. 2022. https://www.who.int/news-room/fact-sheets/detail/yaws
2. World Health Organization. Guidelines for the Treatment of Yaws. 2020. https://apps.who.int/iris/handle/10665/332415
3. Marks M, et al. Single‑dose oral azithromycin for the treatment of yaws. N Engl J Med. 2014;371:411‑422. DOI:10.1056/NEJMoa1306575
4. Cleveland Clinic. Yaws – Diagnosis and Treatment. 2023. https://my.clevelandclinic.org/health/diseases/21155-yaws
5. Mayo Clinic. Treponemal infections: Overview. 2022. https://www.mayoclinic.org/diseases-conditions/treponemal-infections/symptoms-causes/syc-20353836