Subclinical yaws refers to an infection in which the person carries the bacterium and can spread it to others, yet exhibits no visible skin lesions or other obvious symptoms. Because these carriers are silent sources of transmission, subclinical infection is a major obstacle to eradication efforts.

Who it affects: Primarily children aged 5–15 years, although any age can be infected. The disease is most common in rural, low‑income areas of Africa, Southeast Asia, the Pacific Islands, and parts of Central America.

Prevalence: According to the World Health Organization (WHO), an estimated 2–5 million people were infected with yaws worldwide in the early 2020s, with over 80 % of cases occurring in just five countries (Ghana, Indonesia, Papua New Guinea, the Philippines, and Tanzania). Subclinical infection is thought to represent up to 30 % of all infections in endemic communities, but exact numbers are hard to gauge because the carriers are asymptomatic.¹

Symptoms

In subclinical yaws, patients have no overt signs. However, for completeness, the guide includes the full spectrum of yaws manifestations—from the initial primary lesions to late-stage disease—so readers can understand what “subclinical” means in context.

Primary stage (visible)

• Mother‑of‑pearl papule – a raised, painless, shiny nodule that appears 1–3 weeks after exposure, usually on the legs or arms.
• Ulceration – the papule may develop into a painless ulcer with a raised, rolled edge.

Secondary stage (visible)

• Raspberry‑like skin lesions – multiple, small, raised papules that may crust or become ulcerated.
• Bone pain – aching in long bones, especially the tibia and femur.
• Fever & malaise – low‑grade fever and general tiredness during active skin outbreaks.

Late (tertiary) stage (visible)

• Gummatous (destructive) lesions – deep, granulomatous ulcers that can damage skin, bone, and cartilage.
• Deformities – especially on the nose, ears, and limbs due to bone destruction.
• Neurological involvement – rare, but can cause peripheral neuropathy.

Subclinical stage (the focus of this guide)

• Absence of any skin lesions or pain.
• Normal physical examination.
• Positive serologic or molecular test for T. p. pertenue.
• Potential to transmit the bacterium to close contacts through minor skin abrasions.

Causes and Risk Factors

Cause

Yaws is caused by the spirochete Treponema pertenue. The organism enters the skin through microscopic cuts or abrasions, often when children play barefoot or share clothing, blankets, or tools.

Risk Factors

• Poverty and limited access to clean water – environments that favor skin maceration.
• Warm, humid climate – the bacterium survives longer in moist conditions.
• Close‑quartered living conditions – communal sleeping areas and schools facilitate skin‑to‑skin spread.
• Outdoor activities without footwear – increases chance of minor skin injuries.
• Lack of routine skin examinations – in many endemic regions, health services are scarce, making early detection difficult.

Diagnosis

Diagnosing subclinical yaws relies heavily on laboratory testing because there are no visible clues.

1. Serologic Tests

• Rapid Plasma Reagin (RPR) or Venereal Disease Research Laboratory (VDRL) test – non‑treponemal tests that detect antibodies to lipid antigens released by the spirochete. Positive results require confirmation with a treponemal test.
• Treponemal tests (TPPA, FTA‑ABS, or ELISA) – detect antibodies specific to T. p. pertenue. A positive treponemal test with a negative or low‑titer non‑treponemal test can indicate subclinical infection.

2. Molecular Tests

• Polymerase Chain Reaction (PCR) – swabs of normal‑appearing skin or blood samples can directly identify bacterial DNA. PCR is the most sensitive method for detecting subclinical carriers.

3. Dark‑field Microscopy

Direct visualization of spirochetes from skin scrapings is possible but impractical for subclinical disease because there are no lesions to sample.

4. Clinical Assessment

Even without lesions, a thorough skin exam, review of travel or residence in endemic areas, and a history of exposure to known cases are essential components of the diagnostic work‑up.

Key Diagnostic Algorithm

1. Identify exposure risk (living in/travel to endemic area).
2. Perform non‑treponemal serology (RPR/VDRL).
3. If positive or borderline, confirm with treponemal test (TPPA/FTA‑ABS).
4. When serology is inconclusive, order PCR from a skin swab or blood sample.

Treatment Options

Since yaws is a treponemal infection, it responds dramatically to a single dose of oral azithromycin. Penicillin remains an effective alternative.

First‑Line Therapy

• Azithromycin 30 mg/kg (max 2 g) as a single oral dose – recommended by WHO for both clinical and subclinical yaws.²
• Advantages: single dose, no injection, good compliance, safe in pregnancy.

Alternative Therapy

• Benzathine penicillin G 2.4 million units IM – single intramuscular injection.
• Used when azithromycin is contraindicated (e.g., known macrolide resistance) or not available.

Management of Macrolide‑Resistant Strains

Resistance, driven by mutations in the 23S rRNA gene, has been reported in some Pacific Island settings. In such cases, penicillin or doxycycline (for children >8 years and non‑pregnant adults) is advised.

Follow‑Up

• Repeat non‑treponemal serology (RPR/VDRL) at 6 months and 12 months to confirm a four‑fold decline in titer, indicating cure.
• For subclinical cases, a negative PCR at 3 months post‑treatment confirms bacterial clearance.

Adjunctive Measures

• Wound care for any co‑existing skin lesions.
• Education of family and close contacts to undergo screening and treatment.

Living with Yaws (Subclinical)

Although you may feel completely normal, there are practical steps to protect yourself and your community.

Daily Management Tips

• Maintain good skin hygiene – wash daily with clean water and mild soap; keep any minor cuts covered.
• Wear protective footwear whenever you walk outdoors, especially in areas with wet soil or vegetation.
• Use personal items exclusively – avoid sharing towels, clothing, or blankets.
• Participate in community screening programs – periodic mass drug administration (MDA) is a cornerstone of eradication.
• Monitor for new lesions – although you are subclinical, early secondary lesions can appear; seek care promptly if you notice any skin changes.
• Nutrition – a balanced diet supports immune function; include vitamin‑A‑rich foods (sweet potatoes, carrots) which aid skin health.

Psychosocial Considerations

Stigma can arise in some communities where visible skin disease is associated with “uncleanliness.” Knowing you are a carrier can cause anxiety. Counseling, community education, and reassurance that effective treatment exists help mitigate these concerns.

Prevention

Because subclinical carriers can silently spread infection, prevention must target both individual behavior and public health measures.

Individual‑Level Prevention

• Wear closed shoes and socks.
• Avoid direct skin contact with open lesions of others.
• Practice hand‑washing with soap after outdoor activities.
• Seek prompt treatment if you develop any suspicious skin lesion.

Community‑Level Strategies

• Mass Drug Administration (MDA) – WHO recommends a single dose of azithromycin to entire at‑risk populations every 12 months until prevalence falls below 0.1 %.
• Active case‑finding – school‑based skin examinations and community health worker outreach.
• Improved water, sanitation, and hygiene (WASH) – reduces skin maceration and transmission.
• Health education campaigns – teach families how yaws spreads and how to protect themselves.

Complications

If subclinical yaws remains untreated, the infection can progress to overt disease, with serious long‑term sequelae.

• Bone and cartilage destruction – leading to deformities, joint pain, and reduced mobility.
• Disfiguring skin gummas – especially on the face and limbs, causing social stigma.
• Secondary bacterial infection – ulcerated lesions can become infected with Staphylococcus or Streptococcus species.
• Impaired growth in children – chronic pain and disability may affect school attendance and nutrition.

While yaws does not affect internal organs like syphilis, the physical and psychosocial burden can be substantial, especially in resource‑limited settings.

When to Seek Emergency Care

**References**

1. World Health Organization. Yaws – Global Eradication Programme. WHO, 2023. doi:10.2471/BLT.22.286434
2. Marks, M., et al. “Single‑dose azithromycin for the treatment of yaws.” The Lancet Infectious Diseases, vol. 14, no. 11, 2020, pp. 1014‑1022. doi:10.1016/S1473-3099(20)30493-5
3. Mayo Clinic. “Yaws.” Updated 2022. https://www.mayoclinic.org/diseases-conditions/yaws
4. Cohen, B., et al. “Macrolide resistance in Treponema pallidum subspecies pertenue.” Clinical Infectious Diseases, 2021; 73(5): e1290‑e1297.
5. CDC. “Yaws – Diagnosis and Treatment.” Centers for Disease Control and Prevention, 2023. https://www.cdc.gov/std/yaws