|Classification and external resources|
Nodules on the elbow resulting from a Treponema pallidum pertenue bacterial infection
Yaws (also frambesia tropica, thymosis, polypapilloma tropicum, pian or parangi, "Bouba", "Frambösie", and "Pian") is a tropical infection of the skin, bones and joints caused by the spirochete bacterium Treponema pallidum pertenue. Other related treponemal diseases are bejel (Treponema pallidum endemicum), pinta (Treponema pallidum carateum), and syphilis (Treponema pallidum pallidum).
Examination of remains of Homo erectus from Kenya, that are about 1.6 million years old, has revealed signs typical of yaws. The genetic analysis of the yaws' causative bacteria — Treponema pallidum pertenue — has led to the conclusion that yaws is the most ancient of the four known Treponema diseases. All other Treponema pallidum subspecies probably evolved from Treponema pallidum pertenue. Yaws is believed to have originated in tropical areas of Africa, and spread to other tropical areas of the world via immigration and the slave trade. The latter is likely the way it was introduced to Europe from Africa in the 15th century. The first unambiguous description of yaws was made by the Dutch physician Willem Piso. Yaws was clearly described in 1679 among African slaves by Thomas Sydenham in his epistle on venereal diseases, although he thought that it was the same disease as syphilis. The causative agent of yaws was discovered in 1905 by Aldo Castellani in ulcers of patients from Ceylon.
Epidemiology and Clinical presentation
Being T. pallidum pertenue temperature and humidity dependent, yaws is found in humid tropical regions in South America, Africa, Asia and Oceania. The disease is transmitted by skin-to-skin contact with an infective lesion, with the bacterium entering through a pre-existing cut, bite or scratch. Within ninety days (but usually less than a month) of infection a painless but distinctive "mother yaw" appears, which is a painless nodule which enlarges and becomes warty in appearance. Sometimes nearby "daughter yaws" also appear simultaneously. This primary stage resolves completely within six months. The secondary stage occurs months to years later, and is characterised by widespread skin lesions of varying appearance, including "crab yaws" on the palms and soles with desquamation. These secondary lesions frequently ulcerate (and are then highly infectious), but heal after six months or more. About ten percent of people then go on to develop tertiary disease within five to ten years (during which further secondary lesions may come and go), characterised by widespread bone, joint and soft tissue destruction, which may include extensive destruction of the bone and cartilage of the nose (rhinopharyngitis mutilans or "gangosa").
About three quarters of people affected are children under 15 years of age, with the greatest incidence in children 6–10 years old. Therefore, children are the main reservoir of infection.
T. pallidum pertenue has been identified in non-human primates (baboons, chimpanzees, and gorillas) and studies show that experimental inoculation of human beings with a simian isolate causes yaws-like disease. However, no evidence exists of crosstransmission between human beings and primates, but more research is needed to discount the possibility of a yaws animal reservoir in non-human primates.
Mass treatment campaigns in the 1950s reduced the worldwide prevalence from 50–150 million to fewer than 2.5 million; however during the 1970s there were outbreaks in south-east Asia and there have been continued sporadic cases in South America. It is unclear how many people worldwide are infected at present.
Diagnosis and Treatment
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.
Treatment is normally by a single intramuscular injection of penicillin, or by a course of penicillin, erythromycin or tetracycline tablets. A single oral dose of azithromycin was shown to be as effective as intramuscular penicillin. Primary and secondary stage lesions may heal completely, but the destructive changes of tertiary yaws are largely irreversible.
The global prevalence of this disease and the other endemic treponematoses, bejel and pinta, was reduced by the Global Control of Treponematoses (TCP) programme between 1952 and 1964 from about 50 to 150 million cases to about 2.5 million (a 95 percent reduction). Following the cessation of this program yaws surveillance and treatment became a part of primary health systems of the affected countries. However incomplete eradication led to a resurgence of yaws in 1970s with the largest number of case found in the Western Africa region.
Yaws is a relatively easy disease to eradicate. Humans are likely the only reservoir of infection. A single injection of long-acting penicillin or other beta lactam antibiotic cures the disease and is widely available; and the disease is highly localised making case tracing relatively easy.
In April 2012 WHO decided to start a new global campaign for eradication of yaws, which has been on the WHO eradication list since 2011. According to the official roadmap the elimination should be achieved by 2020. So far, this appears to have met with some success, since no cases have been seen in India since 2004. Certification for disease free status requires an absence of the disease for at least five years. In India this happened on 19 September 2011. In 1996 there were 3,571 yaws cases in India; in 1997 after a serious elimination effort began the number of cases fell to 735. By 2003 the number of cases were 46. The last clinical case in India was reported in 2003 and the last latent case in 2006.
In March 2013, a new meeting of yaws expert was convened by WHO in Geneva, to further discuss the strategy to be adopted in the new eradication campaign. The meeting was a significant one, since representatives of almost all countries where yaws is known to be endemic attended and described the epidemiological situation at the national level. The disease is currently known to be present in Indonesia and Timor-Leste in South-East Asia; Papua New Guinea, the Solomon Islands and Vanuatu in the Pacific region; and Benin, Cameroon, Central African Republic, Congo, Côte d'Ivoire, Democratic Republic of Congo, Ghana and Togo in Africa. As reported at the meeting, in several such countries, mapping of the disease is still patchy and will need to be completed before any serious eradication effort could be enforced.
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