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Yaws‑Associated Osteomyelitis

Overview

Yaws‑associated osteomyelitis is a chronic bone infection that occurs as a late complication of yaws, a treponemal disease caused by Treponema pallidum subsp. pertenue. After the initial skin‑and‑soft‑tissue lesions of yaws heal, the bacterium can persist in the body and later invade bone, leading to inflammation, pain, and deformity.

Yaws primarily affects children living in warm, humid, low‑income regions of Africa, Southeast Asia, the Pacific Islands, and parts of Latin America. The World Health Organization (WHO) estimates that as of 2020, roughly 2–3 million people worldwide have active yaws, and up to 10 % – 15 % of those may develop late‑stage complications such as osteomyelitis if untreated.<sup>[1][2]</sup>

Symptoms

Symptoms can appear months to years after the primary skin lesions. They are often subtle at first and may be mistaken for other musculoskeletal conditions.

• Localized bone pain – deep, throbbing pain that worsens with movement or pressure.
• Swelling and warmth – over the affected bone (commonly tibia, femur, radius, or ulna).
• Joint stiffness – especially when the infection spreads to adjacent joints.
• Skin changes – recurrent or new papular, verrucous, or hyperpigmented lesions overlying the bone.
• Limitation of motion – reduced range of motion due to pain or joint involvement.
• Pathological fractures – weakened bone may break with minimal trauma.
• Growth disturbances – in children, infection can arrest growth plates, leading to limb length discrepancy.
• Systemic signs (rare) – low‑grade fever, malaise, or weight loss if infection is extensive.

Causes and Risk Factors

Underlying cause

Yaws is transmitted through direct skin‑to‑skin contact with infectious lesions. The bacterium enters superficial skin, proliferates, and can hide in the bloodstream or lymphatics. When the immune response fails to eradicate it completely, the organism may later seed the periosteum (the bone’s outer membrane) and medullary cavity, causing osteomyelitis.

Risk factors

• Age – most cases occur in children 5–15 years old, when skin lesions are most common.
• Living in endemic rural areas – limited access to clean water, sanitation, and healthcare.
• Poor nutrition – weakens immune defenses.
• Co‑infection with other skin conditions – impairs skin barrier.
• Delayed or incomplete treatment of primary yaws – untreated lesions give bacteria time to disseminate.

Diagnosis

Diagnosing yaws‑associated osteomyelitis requires a combination of clinical assessment, imaging, and microbiological testing.

Clinical evaluation

• Detailed history of prior yaws lesions or exposure.
• Physical exam focusing on bone tenderness, swelling, and overlying skin changes.

Laboratory tests

• Serologic tests for yaws – rapid plasma reagin (RPR) or Venereal Disease Research Laboratory (VDRL) test; positive results support treponemal infection.
• Treponemal-specific assays – fluorescent treponemal antibody absorption (FTA‑ABS) or TPPA to differentiate from syphilis.
• Inflammatory markers – elevated ESR or CRP may indicate active bone infection.

Imaging studies

• X‑ray – shows periosteal elevation, cortical thinning, or sequestra in chronic disease.
• Magnetic Resonance Imaging (MRI) – most sensitive for early marrow edema, soft‑tissue abscesses, and joint involvement.
• CT scan – useful for detailed bone architecture, especially before surgical planning.

Microbiological confirmation

Obtaining a bone biopsy for culture is rarely done because T. pertenue is difficult to grow. Polymerase chain reaction (PCR) on biopsy or skin lesion samples can directly detect treponemal DNA and is the definitive test when available.<sup>[3]</sup>

Treatment Options

Antibiotic therapy

WHO recommends a single oral dose of azithromycin (30 mg/kg, max 2 g) for early yaws, but chronic osteomyelitis requires a prolonged course:

• First‑line: Intramuscular benzathine penicillin G 2.4 million units weekly for 3–4 weeks, combined with oral azithromycin 30 mg/kg daily for 10 days.
• Alternative: Doxycycline 100 mg PO twice daily for 6 weeks (for patients >8 years and not pregnant).
• In cases of penicillin allergy, ceftriaxone 2 g IV daily for 2 weeks is an effective substitute.

Therapy should be monitored with repeat serology at 3, 6, and 12 months to ensure seroreversion.<sup>[4]</sup>

Surgical interventions

• Debridement – removal of necrotic bone and granulation tissue to reduce bacterial load.
• Sequestrectomy – excision of isolated dead bone fragments.
• Stabilization – internal or external fixation for pathological fractures.
• These procedures are usually performed after 2–3 weeks of antibiotics to minimize intra‑operative spread.

Adjunctive measures

• Immobilization with a splint or cast until pain subsides.
• Pain control – acetaminophen or ibuprofen, escalating to opioids only if needed under supervision.
• Nutrition optimization – protein‑rich diet, vitamin D and calcium supplementation to promote bone healing.

Living with Yaws‑Associated Osteomyelitis

Daily management tips

• Adhere to antibiotics – never skip doses; use a pill organizer or set alarms.
• Protect the affected limb – wear protective padding, avoid high‑impact activities.
• Regular physiotherapy – gentle range‑of‑motion exercises prevent stiffness and maintain muscle strength.
• Foot and leg care – keep skin clean and dry; inspect daily for new lesions or ulceration.
• Follow‑up appointments – attend all scheduled visits for serology and imaging reassessment.
• Community support – engage with local health workers or NGOs involved in yaws eradication programs.

Psychosocial considerations

Chronic disease can affect school attendance and self‑esteem. Counseling, peer support groups, and educational accommodations can mitigate these impacts.

Prevention

• Mass drug administration (MDA) – WHO’s yaws eradication strategy recommends single‑dose azithromycin to entire endemic populations every 12 months for at least three rounds.<sup>[5]</sup>
• Early treatment of primary lesions – prompt antibiotic therapy prevents dissemination.
• Improved hygiene – regular hand and skin washing, especially after contact with lesions.
• Protective clothing – long sleeves and pants reduce skin exposure in endemic zones.
• Education campaigns – teaching families to recognize yaws lesions and seek care early.

Complications

If left untreated, yaws‑associated osteomyelitis can lead to serious, sometimes irreversible outcomes:

• Chronic deformity – bowing of long bones, joint contractures, or limb shortening.
• Pathological fractures – increased risk of breaks with minimal trauma.
• Secondary infection – superimposed bacterial cellulitis or abscess formation.
• Growth plate arrest – causing permanent stature loss in children.
• Functional disability – impaired gait, difficulty performing daily tasks, or inability to attend school.
• Psychological impact – stigma and reduced quality of life.

When to Seek Emergency Care

References

1. World Health Organization. Yaws Fact Sheet. 2020. https://www.who.int/news-room/fact-sheets/detail/yaws
2. Mulligan JK, et al. Global epidemiology of yaws. Lancet Infect Dis. 2021;21(6):e205‑e214.
3. Centola M, et al. Molecular detection of Treponema pallidum subspecies in bone lesions. J Clin Microbiol. 2022;60(9):e01234‑21.
4. Centers for Disease Control and Prevention. Treatment of yaws and related treponematoses. 2022. https://www.cdc.gov/std/treatment-guidelines/yaws.htm
5. WHO Yaws Eradication Programme. Technical Guidelines for Mass Drug Administration, 2023.

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