eMedicine Specialties > Dermatology > Bacterial Infections

Yaws

Author: Caroline L Levine, MD, Staff Physician, Department of Dermatology, Emerson Hospital, Mt Aburn Hospital
Contributor Information and Disclosures

Updated: Oct 22, 2009

Introduction

Background

Yaws is the most prevalent infectious, nonvenereal, treponemal disease and is caused by Treponema pallidum subsp pertenue. Yaws is transmitted by direct skin contact and usually affects children, with a peak incidence in those aged 6-10 years. Similar to syphilis, yaws can persist for years as a chronic, relapsing disease.

Yaws continues to be endemic along the tropical belt in areas characterized by hot temperatures, high humidity, and heavy rainfall. These conditions coupled with the persistence of poverty, poor sanitation, overcrowding, and lack of public health surveillance allow for yaws perpetuation.¹

Pathophysiology

Cutaneous lesions characterize the primary and secondary stages of yaws. The tertiary stage of yaws may include involvement of skin, bones, and joints.

Frequency

International

In the early 1950s, the estimated number of active yaws cases in areas of Africa, Asia, South America, Central America, and the Pacific Islands was 25-150 million. After the World Health Organization (WHO) supported mass yaws treatment campaigns from 1954-1963, researchers observed a dramatic fall in the prevalence. Since then, however, cases of yaws rebounded because of the lack of public health surveillance and inadequate treatment facilities.² Currently, researchers estimate that 100 million children are at risk of acquiring yaws.

Mortality/Morbidity

Unless treated, yaws can become a chronic, relapsing disease with skin, bone, and joint involvement. In 10% of yaws cases, patients enter a late stage (tertiary stage) characterized by destructive cutaneous lesions and severely deforming bone and joint lesions. Neurologic and ophthalmologic involvement may also occur in yaws.

Sex

No sexual predilection exists for yaws.

Age

Children serve as the primary reservoir for yaws. Yaws is most common in children younger than 15 years, with the peak incidence occurring between ages 6 and 10 years.

Clinical

History

The typical yaws patient is young and from an endemic area and has been exposed to infected persons with active disease.

Physical

• Primary stage of yaws
  • After an incubation period of 9-90 days (with an average of 3 wks), the primary lesion, or the mother yaw, develops at the site of inoculation after a scratch, a bite, or an abrasion of exposed skin, most commonly on the legs, the feet, or the buttocks.
  • The lesion is a reddish, nontender, and, occasionally, pruritic papulonodule.
  • The mother yaw ulcer develops a honey-brown crust and enlarges horizontally to 1-5 cm in diameter, sometimes coalescing with satellite lesions. The crust frequently sloughs off and reveals a raspberrylike base (hence the synonym frambesia).
  • On rare occasions, a primary lesion is not seen.
  • Because the exudate of the raspberrylike ulcer is teeming with treponemes, these lesions are considered highly infectious.
  • Lymphadenopathy, fever, and joint pain may accompany this stage.
  • The mother yaw resolves spontaneously in 2-9 months, leaving an atrophic scar with central hypopigmentation and peripheral hyperpigmentation.
• Secondary stage of yaws
  • Following a period of latency (about 6-16 wk after the primary stage), an eruption of disseminated skin lesions, bone lesions, and constitutional symptoms appears.
  • The cutaneous lesions, or the daughter yaws, resemble the mother yaw but are smaller (up to 2 cm in diameter) and are frequently located adjacent to body orifices, particularly the mouth and the nose.
  • The daughter yaws expand, ulcerate, and exude a fibrinous fluid teeming with treponemes, which dries into a crust. The exudate attracts flies, which are bothersome to the person who is affected.
  • Occasionally, central resolution yields circinate or annular scaly lesions resembling fungal infections. These lesions are referred to as tinea yaws.
  • Papulosquamous patches and plaques that resemble syphilis may be noted on any part of the body.
  • Lesions in the axillae or the groin resemble condylomata lata; lesions on the mucous membranes resemble hypertrophic mucous patches.
  • Piannic onychia is a paronychia caused by papillomas in the nail fold.
  • Papillomas on the plantar surfaces can form thick, hyperkeratotic plaques that may become fissured or eroded. Lesions are painful and cause a deliberate crablike gait (crab yaws). Macular and hyperkeratotic lesions on the palms and the soles resembling syphilis may also be present.
  • Skeletal involvement includes painful osteoperiostitis and fusiform soft tissue swelling of the metatarsals and the metacarpals. Some of the early bone changes can be seen on radiographs. Periosteal thickening can often be palpable.³
  • Secondary-stage manifestations are generally nonscarring and reversible, subsiding in weeks to months.
  • Patients may develop relapses at intervals up to 5 years after infection. Relapsing lesions tend to occur in the perioral, perianal, and periaxillary areas. The disease then enters a noninfectious latent period, and patients do not exhibit any signs or symptoms.
• Tertiary stage of yaws
  • In about 10% of cases, after 5-15 years of latency, a late stage develops, characterized by destructive skin lesions, bone lesions, and possible neurologic and ophthalmologic involvement.
  • Progressively enlarging, painless, subcutaneous nodules develop, which undergo abscess formation, necrosis, and ulceration. Lesions have well-defined edges and an indurated base with granulation tissue and yellowish slough.
  • Ulcers may become infected, causing destruction of underlying structures. They may also coalesce, forming serpiginous tracts that heal with keloid formation, which leads to crippling deformities and contractures.
  • Hyperkeratosis and keratoderma of the palms and the soles as well as juxta-articular ulcerated gummatous nodules may accompany lesions.
  • Late skeletal lesions consist of hypertrophic periostitis, gummatous periostitis, osteitis, and osteomyelitis. Chronic osteitis of the tibia can lead to saber shins. In about 1% of patients, bilateral hypertrophic osteitis of the external aspects of the nasal processes of the maxillae with persistent swelling occurs. This condition is referred to as goundou, which slowly progresses over 5-20 years and eventually may lead to massive destruction and perforation of the nose and the palate (gangosa).
  • Neurologic and ophthalmologic involvement is debated in the literature. Some reports suggest that disc atrophy, optic atrophy, and myeloneuropathies may occur.
• Attenuated yaws
  • Some reports describe an attenuated, less contagious form of yaws in areas of low disease prevalence.
  • A solitary patch or a few, dry, flat, gray patches confined to the skin folds characterize attenuated yaws.

Causes

Yaws is caused by T pallidum subsp pertenue, a slender spirochete, which is serologically indistinguishable from the spirochete that causes syphilis (T pallidum). Like the other nonvenereal treponematoses, yaws is not found in urban centers, it is not sexually transmitted, and it is not congenitally acquired. Children serve as the primary reservoir for yaws, spreading the disease via skin-to-skin and skin-to-mucous membrane contact.

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