Yaws is a tropical infection of the skin, bones and joints caused by the spirochete bacterium Treponema pallidum pertenue. The disease begins with a round, hard swelling of the skin, 2 to 5 centimeters in diameter. The center may break open and form an ulcer. This initial skin lesion typically heals after three to six months. After weeks to years, joints and bones may become painful, fatigue may develop, and new skin lesions may appear. The skin of the palms of the hands and the soles of the feet may become thick and break open.The bones (especially those of the nose) may become misshapen. After five years or more large areas of skin may die, leaving a scar. Yaws is spread by direct contact with the fluid from a lesion of an infected person. The contact is usually of a non-sexual nature. The disease is most common among children, who spread it by playing together. Other related treponemal diseases are bejel (Treponema pallidum endemicum), pinta (Treponema pallidum carateum), and syphilis (Treponema pallidum pallidum). Yaws is often diagnosed by the appearance of the lesions. Blood antibody tests may be useful but cannot separate previous from current infections. Polymerase chain reaction (PCR) is the most accurate method of diagnosis. The three signs of the disease:
- painless ulcer with scab
- palmar/plantar hyperkeratosis (thickening).
Without treatment, physical deformities occur in 10% of cases. Yaws is a chronic infection that affects mainly the skin, bone and cartilage. The disease occurs mainly in poor communities in warm, humid, tropical areas of Africa, Asia and Latin America. The causative organism is a bacterium called Treponema pertenue, a subspecies of Treponema pallidum that causes venereal syphilis. However, yaws is a non-venereal infection.
About 75% of people affected are children under 15 years of age (peak incidence occurs in children aged 6-10 years); males and females are affected and no race is exempt. Yaws is transmitted mainly through direct skin contact with an infected person. A single skin lesion develops at the point of entry of the bacterium after 2–4 weeks. Without treatment, multiple lesions appear all over the body. Overcrowding, poor personal hygiene and poor sanitation facilitate the spread of the disease. The disease is rarely fatal, however, it can lead to chronic disfigurement and disability.
Most often the diagnosis is made clinically. Dark field microscopy of samples taken from early lesions (particularly ulcerative lesions) may show the responsible organism. Blood tests such as VDRL, Rapid Plasma Reagin (RPR) and TPHA will also be positive, but there are no current blood tests which distinguish among the four treponematoses. Prevention is, in part, by curing those who have the disease thereby decreasing the risk of transmission. Where the disease is common, treating the entire community is effective. Improving cleanliness and sanitation will also decrease spread. Treatment is typically with antibiotics including: azithromycin by mouth or benzathine penicillin by injection. Yaws can be treated with a single dose of a cheap and effective antibiotic: Benzathine Penicillin injection cures the disease.