yaws

yaws
Name	Yaws
Field	Tropical medicine, Infectious disease (medical specialty)

yaws. Yaws is a chronic, disfiguring, but non-fatal bacterial infection primarily affecting the skin, bones, and cartilage. It is one of the neglected tropical diseases targeted for global eradication by the World Health Organization. The disease is caused by the spirochete bacterium Treponema pallidum subspecies *pertenue*, a close relative of the organism that causes syphilis. Historically widespread in tropical regions across Africa, Asia, and the Americas, yaws has seen a dramatic reduction in prevalence due to concerted public health campaigns.

Overview

Yaws belongs to the group of diseases known as the endemic treponematoses, which also includes bejel and pinta. The infection is not sexually transmitted but spreads through direct skin-to-skin contact with an infected lesion, typically among children living in poor, rural communities with limited access to sanitation and clean water. Major historical control programs, notably those led by the World Health Organization and UNICEF in the mid-20th century, demonstrated the feasibility of eradication through mass administration of penicillin. Despite a significant resurgence in later decades, a renewed global initiative launched in 2012 aims to eliminate yaws by 2030, utilizing a single oral dose of azithromycin.

Causes and transmission

The causative agent of yaws is the bacterium Treponema pallidum subspecies *pertenue*. This spirochete is morphologically and serologically indistinguishable from the subspecies that causes syphilis, but it is genetically distinct and results in a different disease presentation. Transmission occurs through direct, non-sexual contact with the infectious exudate from early skin lesions of an infected person. Minor skin trauma facilitates entry of the bacterium. The disease is strongly associated with poverty, overcrowding, and poor personal hygiene, and it primarily affects children under 15 years of age. Flies of the genus Hippelates have been investigated as potential mechanical vectors, but person-to-person contact is considered the primary route.

Signs and symptoms

The disease progresses through distinct clinical stages. The primary stage, appearing 3-5 weeks after infection, features a single, painless, raspberry-like papule known as a "mother yaw" at the site of inoculation, often on the legs. This lesion is highly infectious and may persist for months. The secondary stage, occurring weeks to months later, involves a generalized eruption of similar, smaller, infectious papules and plaques across the skin. Late stage yaws, developing after 5 or more years in untreated individuals, is non-infectious but destructive, causing lesions of the skin and bones. These can lead to severe disfigurement, including gangosa (destruction of the nose and palate) and sabre tibia (anterior bowing of the shin bone).

Diagnosis

Diagnosis in endemic areas is primarily based on clinical recognition of the characteristic lesions. Laboratory confirmation can be challenging. Dark-field microscopy of exudate from an early lesion can visualize the motile Treponema pallidum organisms. Serological tests used for syphilis, such as the Rapid Plasma Reagin test and the Treponema pallidum particle agglutination assay, are also reactive in yaws but cannot distinguish between the different treponemal infections. Molecular techniques like polymerase chain reaction are used in reference laboratories to differentiate *T. p. pertenue* from other subspecies but are not widely available in field settings.

Treatment and prevention

Treatment is highly effective. The historical standard, established during the World Health Organization eradication campaign of the 1950s, was a single intramuscular injection of benzathine benzylpenicillin. The current strategy, based on research from Lihir Island in Papua New Guinea, employs a single oral dose of azithromycin, which simplifies large-scale community treatment. The Morges Strategy, endorsed by the World Health Organization, calls for total community mass treatment with azithromycin in endemic districts, followed by targeted treatment of active cases and their contacts. Prevention relies on breaking the chain of transmission through early diagnosis, treatment, and improved living conditions.

Epidemiology and eradication efforts

Yaws is endemic in warm, humid, tropical areas of Africa, Asia, and the Western Pacific. Countries with recent known transmission include Papua New Guinea, Solomon Islands, Ghana, and Cameroon. The first global eradication program from 1952 to 1964, a joint effort by the World Health Organization and UNICEF, reduced global prevalence by over 95% but was not sustained. A resurgence prompted a new initiative in 2012. Landmark studies published in *The Lancet* demonstrated the efficacy of oral azithromycin. The ongoing effort, aligned with the London Declaration on Neglected Tropical Diseases, faces challenges including drug resistance surveillance, reaching remote populations, and securing sustained funding from partners like the Bill & Melinda Gates Foundation.

Category:Neglected tropical diseases Category:Bacterial diseases Category:Eradicated diseases