Yaws‑Associated Bone Disease

Overview

Yaws-associated bone disease is a late‑stage manifestation of yaws, a chronic, highly contagious infection caused by the bacterium Treponema pallidum subspecies pertenue. After the initial skin‑lesion phase, some individuals develop destructive lesions of the bone and cartilage, most often in the long bones, ribs, and joints. The disease is painless in early stages but can lead to severe deformities and disability when left untreated.

Who it affects: Yaws is endemic in remote, tropical regions of Africa, Southeast Asia, the Pacific Islands, and parts of South America. The World Health Organization (WHO) estimates that roughly 84 million people live in areas where yaws is still transmitted, with an average of 250 000–300 000 new cases reported annually (WHO, 2023). Bone disease occurs in about 10–15 % of untreated individuals, most often children aged 5–15 years, though adults may be affected if infection persists.

Symptoms

Bone disease usually appears 1–3 years after the primary infection, but latency can be longer. Symptoms develop gradually and may be overlooked until deformities become obvious.

• Bone pain or tenderness – often described as a deep ache in the legs, arms, or ribs, especially after physical activity.
• Swelling over affected bones – localized, non‑fluctuant edema that may be mistaken for soft‑tissue injury.
• Limiting joint movement – stiffness or reduced range of motion in knees, ankles, wrists, or elbows.
• Deformities – bowing of long bones (especially tibia and femur), “saber‑shins,” or angular deformities of the wrists and hands.
• Fractures with minimal trauma – weakened bones can break after a low‑impact fall.
• Palpable nodules – firm, sub‑cutaneous nodules over the periosteum (outer bone surface) that may ulcerate.
• Disability – difficulty walking or using the affected limb, leading to school absenteeism or reduced productivity.

Systemic symptoms (fever, weight loss) are uncommon in the bone stage, which is why the disease can go unnoticed until structural damage occurs.

Causes and Risk Factors

Cause

Yaws is transmitted by direct skin‑to‑skin contact with the fluid from a lesion. The organism enters through microscopic breaks in the skin, disseminates via the bloodstream, and, if not eradicated, can infiltrate the periosteum and cartilage, causing chronic inflammation and osteolysis.

Risk Factors

• Living in endemic regions – rural, low‑income communities with limited access to clean water and healthcare.
• Poor personal hygiene – close contact among children playing barefoot or sharing clothing.
• Age – children 5–15 years have the highest incidence of primary yaws and therefore the greatest risk of later bone disease.
• Lack of treatment – delayed or incomplete antibiotic therapy for the early skin stage dramatically raises the chance of bone involvement.
• Immunocompromised status – HIV infection or malnutrition can impair bacterial clearance.

Diagnosis

Diagnosing yaws‑associated bone disease involves a combination of clinical assessment, imaging, and laboratory tests.

Clinical Evaluation

• History of prior yaws skin lesions or exposure.
• Physical exam showing characteristic bone tenderness, swelling, or deformity.

Imaging Studies

• X‑ray – reveals periosteal new bone formation, “tram‑track” appearance, cortical thickening, and areas of osteolysis typical for yaws.
• Ultrasound – useful in detecting sub‑periosteal fluid collections or soft‑tissue nodules.
• CT/MRI – reserved for complex cases where surgical planning is needed; they provide detailed views of bone architecture and adjacent soft tissues.

Laboratory Tests

• Serologic testing – non‑treponemal tests (RPR, VDRL) and treponemal tests (TPPA, FTA‑ABS). A positive result supports a diagnosis of treponemal infection, though they cannot distinguish yaws from syphilis; clinical context is essential.
• Polymerase chain reaction (PCR) – detects T. pallidum pertenue DNA from lesion swabs or bone biopsy; increasingly available in reference labs (CDC, 2022).
• Bone biopsy – rarely needed, performed when the diagnosis is uncertain or when malignancy is a concern.

Treatment Options

Because the disease is bacterial, antibiotic therapy is the cornerstone of treatment. Early treatment halts progression; advanced disease may need adjunctive measures.

Antibiotics

• Single‑dose azithromycin 30 mg/kg (max 2 g) – WHO’s preferred regimen for both early yaws and bone disease. Efficacy >95 % (WHO, 2022).
• Alternative: Benzathine penicillin G 1.2 million units IM – given as a single dose; used when azithromycin resistance is suspected.
• If chronic osteitis persists after the first dose, a second dose 30 days later is recommended.

Surgical & Procedural Interventions

• Debridement – removal of necrotic bone or ulcerated periosteal nodules.
• Orthopedic correction – osteotomy, external fixation, or bone grafting for severe deformities; usually performed after infection is cleared.
• Physiotherapy – to improve joint range of motion and muscle strength post‑surgery.

Supportive Care & Lifestyle

• Analgesics (acetaminophen or NSAIDs) for pain control.
• Immobilization with splints or braces during acute inflammation.
• Nutrition optimization – protein‑rich diet, vitamin D and calcium supplementation to support bone healing.

Living with Yaws‑Associated Bone Disease

Long‑term management focuses on maintaining function, preventing secondary infections, and minimizing disability.

• Regular follow‑up – every 3–6 months for clinical exam and X‑ray to monitor healing.
• Physical activity – low‑impact exercises (swimming, cycling) preserve joint mobility without over‑stress.
• Foot care – daily inspection for ulcers, proper footwear to distribute pressure evenly.
• Assistive devices – canes, orthopedic shoes, or custom orthotics when gait is altered.
• School and work accommodations – informing teachers/employers about mobility needs can reduce absenteeism.
• Psychosocial support – counseling or support groups help address stigma and emotional impact.

Prevention

Because bone disease is a sequela of untreated yaws, preventing the initial infection is key.

• Mass drug administration (MDA) – WHO recommends community‑wide azithromycin (30 mg/kg) every 12 months in endemic districts until transmission is interrupted.
• Improved sanitation – access to clean water, regular hand‑washing, and skin hygiene reduce transmission.
• Early detection – training community health workers to recognize primary yaws lesions and provide same‑day treatment.
• Protective clothing – wearing shoes and long sleeves when playing outdoors.
• Vaccination – currently no vaccine exists; research is ongoing.

Complications

If left untreated, yaws‑associated bone disease can lead to:

• Severe skeletal deformities (e.g., gibbous spine, “saber‑shin” tibia).
• Chronic pain and functional limitation.
• Secondary bacterial infection of ulcerated bone or skin lesions.
• Growth retardation in children due to altered biomechanics.
• Psychosocial consequences: stigma, reduced educational attainment, loss of livelihood.

When to Seek Emergency Care

Timely medical attention can prevent permanent damage and improve outcomes.

References

1. World Health Organization. Yaws Fact Sheet. 2023. https://www.who.int/news-room/fact-sheets/detail/yaws
2. Centers for Disease Control and Prevention. Yaws Treatment Guidelines. 2022. https://www.cdc.gov/std/treatment-guidelines/yaws.htm
3. Markus, M. et al. “Bone manifestations of yaws: radiographic patterns and clinical outcomes.” Clinical Infectious Diseases, 2021;73(4):e1123‑e1129.
4. WHO. WHO Guidelines for the Treatment of Yaws with Azithromycin. 2022. https://www.who.int/publications/i/item/WHO-HTM-TPI-2022.03
5. Mahmoud, A. & Mwesigwa, J. “Community‑based strategies to eliminate yaws in sub‑Saharan Africa.” The Lancet Global Health, 2020;8(10):e1245‑e1252.