Yaws
Encyclopedia
Yaws is a tropical infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 of the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

, bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

s and joints caused by the spirochete bacterium Treponema pallidum pertenue. Other treponemal diseases are bejel
Bejel
Bejel, or endemic syphilis, is a chronic skin and tissue disease caused by infection by a subspecies of the spirochete Treponema pallidum....

 (Treponema pallidum endemicum), pinta
Pinta (disease)
Pinta is a human skin disease endemic to Mexico, Central America, and South America. It is caused by infection with a spirochete, Treponema pallidum carateum, which is morphologically and serologically indistinguishable from the organism that causes syphilis.-Presentation:Pinta is thought to be...

 (Treponema pallidum carateum), and syphilis
Syphilis
Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...

 (Treponema pallidum pallidum).

History

Examination of ancient remains has led to the suggestion that yaws has affected hominid
Hominidae
The Hominidae or include them .), as the term is used here, form a taxonomic family, including four extant genera: chimpanzees , gorillas , humans , and orangutans ....

s for the last 1.5 million years. The current name is believed to be of Carib origin, "yaya" meaning sore. It is believed to have originated in tropical areas of Africa, and spread to other tropical areas of the world via immigration and slave trade.

Epidemiology

Yaws is found in humid tropical regions in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

 and Oceania
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...

. Mass treatment campaigns in the 1950s reduced the worldwide prevalence
Prevalence
In epidemiology, the prevalence of a health-related state in a statistical population is defined as the total number of cases of the risk factor in the population at a given time, or the total number of cases in the population, divided by the number of individuals in the population...

 from 50-100 million to fewer than 2 million; however during the 1970s there were outbreaks in south-east Asia and there have been continued sporadic cases in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

. It is unclear how many people worldwide are infected at present.

Presentation

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
Nodule (medicine)
For use of the term nodule in dermatology, see Nodule In medicine, a nodule refers to a relatively hard, roughly spherical abnormal structure....

 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
Desquamation
Desquamation , also called skin peeling, is the shedding of the outermost membrane or layer of a tissue, such as the skin.-Skin:Normal, nonpathologic desquamation of the skin occurs when keratinocytes, after moving apically over about 14 days, are individually shed unnoticeably...

. 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
Soft tissue
In anatomy, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body, not being bone. Soft tissue includes tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes , and muscles, nerves and blood vessels .It is sometimes...

 destruction, which may include extensive destruction of the bone and cartilage of the nose (rhinopharyngitis mutilans or 'gangosa').

Diagnosis

Dark field microscopy
Dark field microscopy
Dark field microscopy describes microscopy methods, in both light and electron microscopy, which exclude the unscattered beam from the image. As a result, the field around the specimen Dark field microscopy (dark ground microscopy) describes microscopy methods, in both light and electron...

 of samples taken from early lesions (particularly ulcerative lesions) may show the responsible organism. Blood tests such as VDRL, Rapid Plasma Reagin
Rapid Plasma Reagin
Rapid Plasma Reagin refers to a type of test that looks for non-specific antibodies in the blood of the patient that may indicate that the organism that causes syphilis is present...

 (RPR) and TPHA will also be positive, but there are no current blood tests which distinguish among the four treponematoses
Treponematosis
Treponematosis is a term used to collectively or individually describe any of the diseases caused by the bacterial species Treponema pallidum. There are four subspecies described which cause the following diseases:* Syphilis...

.

Treatment

Treatment is normally by a single dose of intramuscular penicillin
Penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

, or by a course of penicillin
Penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

, erythromycin
Erythromycin
Erythromycin is a macrolide antibiotic that has an antimicrobial spectrum similar to or slightly wider than that of penicillin, and is often used for people who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including mycoplasma and...

 or tetracycline tablets. Primary and secondary stage lesions may heal completely, but the destructive changes of tertiary yaws are largely irreversible.

Eradication efforts

The global prevalence of this disease and the other endemic trematoses, Bejel
Bejel
Bejel, or endemic syphilis, is a chronic skin and tissue disease caused by infection by a subspecies of the spirochete Treponema pallidum....

 and Pinta
Pinta (disease)
Pinta is a human skin disease endemic to Mexico, Central America, and South America. It is caused by infection with a spirochete, Treponema pallidum carateum, which is morphologically and serologically indistinguishable from the organism that causes syphilis.-Presentation:Pinta is thought to be...

, was reduced by the Global Control of Treponematoses (TCP) programme between 1952 and 1964 from about 50 million cases to about 2.5 million (a 95 percent reduction). However, following the cessation of this program these diseases remained at a low prevalence in parts of Asia, Africa and the Americas with sporadic outbreaks.

Yaws is a relatively easy disease to eradicate. Man is 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.

Yaws is currently targeted by the South-East Asian Regional Office of the WHO for elimination from the remaining endemic countries in this region (India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

 and East Timor
East Timor
The Democratic Republic of Timor-Leste, commonly known as East Timor , is a state in Southeast Asia. It comprises the eastern half of the island of Timor, the nearby islands of Atauro and Jaco, and Oecusse, an exclave on the northwestern side of the island, within Indonesian West Timor...

) by 2010. 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 5 years. 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. On September 19th 2011 India will be able to apply for certification for the eradication of yaws.
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