Background
Yaws is a contagious, nonvenereal, treponemal infection in humans that mainly occurs in children younger than 15 years. Infection with Treponema pertenue, a subspecies of Treponema pallidum, causes the disease, which occurs primarily in warm, humid, tropical areas of Africa, Asia, South America, and Oceania among poor rural populations where conditions of overcrowding and poor sanitation prevail.
Pathophysiology
The major route of infection is through direct person-to-person contact. The treponemes associated with yaws are located primarily in the epidermis. The ulcerative skin lesions that develop early in the disease course are teeming with spirochetes, which can be transmitted via direct skin-to-skin contact and via breaks in the skin due to trauma, bites, or excoriations.
Yaws, like syphilis, has been classified into the following 4 stages:
- Primary stage: The initial yaws lesion develops at the inoculation site.
- Secondary stage: Widespread dissemination of treponemes results in multiple skin lesions similar to the primary yaws lesion.
- Latent stage: Symptoms are usually absent, but skin lesions can relapse.
- Tertiary stage: Bone, joint, and soft tissue deformities may occur.
Another classification distinguishes early yaws from late yaws. Early yaws includes primary and secondary stages and is characterized by the presence of contagious skin lesions. Late yaws includes the tertiary stage, when lesions are not contagious.
Epidemiology
Frequency
United States
Yaws does not occur in the United States.
International
An estimated 50-100 million persons were infected with yaws before mass treatment campaigns in the 1950s. In the 1970s, yaws cases declined to fewer than 2 million. In the 1980s, fewer than 500 cases per year were reported in the Western Hemisphere. A resurgence of yaws has occurred in West and Central Africa, Southeast Asia, and the Pacific Islands, with recent outbreaks in Thailand, India, Indonesia, Papua New Guinea, and the Solomon Islands. Sporadic cases are reported in South America.
Mortality/Morbidity
- In most patients, yaws remains limited to the skin, but early bone and joint involvement can occur. Although yaws lesions disappear spontaneously, secondary bacterial infections and scarring are common complications.
- After 5-10 years, 10% of untreated patients develop destructive lesions that involve bone, cartilage, skin, and soft tissue, similar to those seen in tertiary syphilis. In contrast to venereal syphilis, cardiovascular and neurological abnormalities almost never occur in patients with yaws.
Sex
- Yaws has no sexual predilection.
Age
- Yaws predominantly affects children younger than 15 years. The peak incidence is in children aged 6-10 years.
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