Yaws is a tropical infection of the skin, bones and joints caused by the spirochete bacterium Treponema pertenue. 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. The sore appears as a "raspberry-like" growth or group of papules at the site of infection and is usually painless. These lesions may persist for months. Additional satellite lesions may appear shortly before or after the mother yaw heals. Children may also develop inflammation of the bones and fingers.
The final stage involves destructive lesions of the skin and bones which can lead to severe disfigurement and disability. It occurs in up to 20% of untreated individuals
Yaws tends to strike children, particularly between the ages of two and five. It is common in areas where poverty and overcrowding interfere with good hygiene practices. The most common locations are in rural areas throughout Africa, Southeast Asia, and in locations bordering the equator in the Americas.
Yaws is transmitted by direct contact with skin lesions of infected people. Approximately two to four weeks after infection, the child develops a sore "mother yaw" where the organism entered the skin.
If untreated a secondary stage occurs after up to four months of latency, it is marked by more 'raspberry' growths but smaller and ulcerous - exuding a thin, highly infective fluid which attracts flies. These growths may also merge together into thick fissured plaques, which can occur on the feet and induce a distinctive gait. These secondary growths are irreversible but there can be relapsing lesions and asymptomatic periods.
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:
1. Primary stage: The initial yaws lesion develops at the inoculation site.
2. Secondary stage: Widespread dissemination of treponemes results in multiple skin lesions similar to the primary yaws lesion.
3. Latent stage: Symptoms are usually absent, but skin lesions can relapse.
4. 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.
In 10-20% of cases the disease can progress over a decade or more to a tertiary stage with destructive lesions of the skin and bones. Large subcutaneous nodules develop and grow before abscessing and ulcerating, these can become infected and may merge together forming serpiginous tracts. These tracts heal with keloid formation which can cause deformities, disabilities and limb contractures. The bone lesions caused are periostitis, osteitis, and osteomyelitis, damage to the tibia can lead to a condition known as sabre shins. In a very few cases a condition known as goundou is caused where growths on the nasal maxillae can result in extensive and severe damage to the nose and palate.

Symptoms
Initial, single skin lesion that may grow slowly and have a raspberry-like appearance. It may also form an ulcer and is usually painless.
• Satellite lesions which may become large nodules/growths throughout the body and may have superficial erosions in secondary yaws.
• Fever may be present in secondary yaws.
• Bone pain/bone destruction; saber shins.
• Finger inflammation (dactylitis).
The first symptom of yaws occurs three to four weeks after acquiring the bacteria. The area where the bacteria originally entered the skin becomes a noticeable bump (papule). The papule grows larger and develops a punched-out center (ulcer), covered with a yellow crust. Lymph nodes in the area may become swollen and tender. This first papule may take as long as six months to heal. Secondary soft, gummy growths then appear on the face, arms and legs, and buttocks. These soft, tumor-like masses may grow on the soles of the feet, causing the patient to walk in an odd and characteristic fashion on the sides of his or her feet (nicknamed "crab yaws"). More destructive tumors may then disrupt the bones of the face, the jaw, and the lower leg. Ulcers around the nose and on the face may be very mutilating.
The largest group afflicted by Yaws are children aged 6 to 10 years in the Caribbean Islands, Latin America, West Africa, India, Oceania or Southeast Asia. There were World Health Organization funded campaigns against yaws from 1954 to 1963 which greatly reduced the incidence of the disease, although more recently numbers have risen again.

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.
• Examination of ancient remains has led to the suggestion that yaws has affected hominids for the last 1.5 million years. The current name is believed to be of Carib origin, "yaya" meaning sore; frambesia is a Modern Latin word inspired by the French word framboise ("raspberry").

Exams and Tests
The diagnosis can be confirmed by examining a sample from a skin lesion under a special type of microscope (darkfield examination). There is no specific blood test for yaws, but because it is closely related to the bacterium that causes syphilis, the blood tests for syphilis may be positive in yaws as well. The disease is identified from blood tests or by a lesion sample through a darkfield examination under a microscope. Treatment is by a single dose of penicillin, erythromycin or tetracycline, recurrence or relapse is uncommon.

Treatment
The mainstay of treatment is a single dose of penicillin G. Relapse is rare. The goals of pharmacotherapy are to reduce morbidity and to prevent complications. Penicillin is rapidly effective in killing the spirochete and in curing yaws except in the tertiary stage, when oxophenarsine with bismuth subsalicylate is used. Prevention centres on isolating and promptly treating cases to reduce exposure and on maintaining personal and group hygiene. All abrasions and sores of the skin and mucous membranes should be treated with appropriate antiseptics and covered with clean dressings, and all clothing in contact with yaws lesions should be sterilized or destroyed.

Possible Complications
Yaws can be disfiguring and disabling because it may cause gross destruction of the skin and bones. It can also cause deformities of the legs, nose, palate, and upper jaw.

Prevention
Mass campaigns for eradication of yaws via penicillin treatment in the 1950s and 1960s have dramatically decreased the worldwide incidence of yaws. Contact the medical provider if you or your child have a chronic skin or bone lesion and have resided in tropical areas where yaws is known to occur.