Yaws Epidemiology

Organism Treponema pallidum subspecies pertenue.

Clinical features Yaws is a non-venereal treponemal disease affecting both the skin and bone. It commences as a primary papule that starts to heal, but after a period, varying from a few weeks to several months, it is followed by generalized lesions, multiple rounded papules, scattered all over the body. These lesions exude serum, which is highly infectious. There is also a mild periostitis in focal bony sites, but these and the skin lesions normally heal with little residual damage. It is the tertiary stage that appears after an asymptomatic period and some 5 years after initial infection that results in gross damage to skin and bone, leading to hideous deformities. The opposite ends of the body are affected with destructive lesions of the nasal bones (gangoza) and scarring, and deformity of the lower limbs (sabre tibia).

Diagnosis is by finding T. p. pertenue in the exudates of lesions. In the motile state, the spirochete can be seen by dark ground microscopy or stained by Giemsa or silver salts. The serological tests for syphilis (Section 14.4) are positive.

Transmission Yaws is a disease of poor hygiene, with close bodily contact being the manner in which infection is commonly transmitted. Flies may be involved in transmission from clothing and dressings that have become contaminated by fluid from sores. The spirochete cannot penetrate unbroken skin, but requires a minor skin abrasion or cut by which to enter.

© R. Webber 2005. Communicable Disease Epidemiology and Control, 2nd edition (Roger Webber)

Incubation period 2-8 weeks.

Period of communicability can be as long as moist lesions persist in the untreated case, which can be several years.

Occurrence and distribution Yaws is predominantly an infection of children, with the mother becoming infected if she did not acquire her infection in childhood. The large overcrowded family with a poor standard of hygiene is the characteristic environment in which yaws so readily spreads. The need to stay indoors and keep close together for warmth in the rainy season might be the reason why the disease is more common at this time of year.

Yaws is restricted to the moist tropical areas of the world in a band that passes through the Caribbean, South America, Africa, Southeast Asia and the Pacific Islands (Fig. 14.1). A resurgence of cases has occurred in West Africa, India, Southeast Asia, Pacific Islands, South America and the Caribbean.

Control and prevention Yaws with its rapid response to a single injection of penicillin has been the subject of successful mass treatment campaigns in the endemic parts of the world. Treatment in a mass campaign is to:

• all those with clinical signs of yaws;

• household, school and other close contacts;

• any person suspected of incubating the disease.

The campaign is preceded by health education encouraging all people to come forward with any suspicious lesions. Each village is visited in turn, everyone examined and treatment given to cases, contacts or suspects. A follow-up surveillance service treats missed cases or new infections. This can readily be done by an effective rural health service.

The success of the WHO mass campaigns against yaws resulted in the virtual disappearance of the disease from many areas, but unfortunately, there is now a resurgence. Newly trained health personnel are unaware of the disease and penicillin has been replaced by other antibiotics in the treatment of common infections.

In the long term, improvements in the level of hygiene and socio-economic status will reduce the conditions in which yaws thrives.

Treatment is a single injection of benzathine penicillin G (1.2 million units for an adult, 0.6 million units for a child). Response is very satisfactory and lesions heal within 2-3 weeks.

Surveillance Due to the possible appearance of new cases, a continuing awareness of the disease needs to be kept, with the taking of smears from any suspicious lesions. It is likely that search will discover more cases, so treat cases and contacts along the same lines as in the eradication campaigns.

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