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What Is Yaws?

Medically Reviewed on 8/5/2021
Yaws is an infectious disease that mainly occurs in the tropical areas of South and Central America, Asia, Africa, and the Pacific Islands. The disease is caused by a bacterium called <i>Treponema pertenue</i>, which causes lesions that look like bumps on the skin of the feet, hands, face, and genital area. Yaws is treated with penicillin or another antibiotic.
Yaws is an infectious disease that mainly occurs in the tropical areas of South and Central America, Asia, Africa, and the Pacific Islands. The disease is caused by a bacterium called Treponema pertenue, which causes lesions that look like bumps on the skin of the feet, hands, face, and genital area. Yaws is treated with penicillin or another antibiotic.

Yaws is a common chronic infectious disease that occurs mainly in warm humid regions such as the tropical areas of Africa, Asia, South and Central Americas, plus the Pacific Islands. The disease has many names (for example, pian, parangi, paru, frambesia tropica). Yaws usually features lesions that appear as bumps on the skin of the face, hands, feet, and genital area. 

Almost all cases of yaws begin in children under 15 years of age, with the peak incidence in 6- to 10-year-old children. The incidence is about the same in males and females. Yaws is a member of the treponematoses, which are diseases caused by spiral bacteria in the genus Treponema.

Besides yaws, the disease includes endemic syphilis (bejel) and pinta. Of these three diseases, yaws is the most common.

What are the symptoms of yaws?

  • Yaws most often starts as a single lesion that becomes slightly elevated, develops a crust that is shed, leaving a base that resembles the texture of a raspberry or strawberry.
  • This primary lesion is termed the mother yaw (also termed buba, buba madre, or primary frambesioma). Secondary lesions, termed daughter yaws, develop in about six to 16 weeks after the primary lesion.

What causes yaws?

  • Yaws is caused by a particular bacterium called a spirochete (a spiral-shaped type of bacteria). The bacterium is scientifically referred to as Treponema pertenue. This organism is considered by some investigators to be a subspecies of T. pallidum, the organism that causes syphilis (a systemic sexually-transmitted disease).
  • Other investigators consider it to be a closely related but separate species of Treponema. T. carateum, the cause of pinta (a skin infection with bluish-black spots), is also closely related to T. pertenue.
  • The history of yaws is unclear; the first possible mention of the disease is considered to be in the Old Testament. D. Bruce and D. Nabarro discovered the spirochete causing yaws (T. pertenue) in 1905.

What are risk factors for yaws?

  • The main risk factor for yaws is direct contact with another person (nonsexual contact) that has yaws lesions on the skin or being a member of the community where yaws infections are endemic.
  • The bacteria that cause yaws only infect humans if there is a break (cut) or abrasion of the skin.
  • Consequently, having a break (cut) or abrasion of the skin while in a geographic area where yaws is endemic is another risk factor for yaws.
  • Poor hygiene and crowded conditions are also risk factors.

How does yaws begin and spread?

  • Yaws begins when T. pertenue penetrates the skin at a site where skin was scraped, cut, or otherwise compromised. In most cases, T. pertenue is transmitted from person to person.
  • At the entrance site, a painless small lesion, or bump, arises within two to eight weeks and grows. The initial lesion is referred to as the mother yaw.
  • The lymph nodes in the area of the mother yaw are often swollen (regional lymphadenopathy). When the mother yaw heals, a light-colored scar remains.

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Why is this disease called yaws?

  • The term yaws is thought to be of Caribbean origin. In the language of the Carib Indian people, yaya is the word for "a sore."
  • Alternatively, the disease term yaws may have come from Africa where the word yaw may have meant "a berry."
  • Because the lesions of yaws look like berries, the disease is also called frambesia (or frambesia tropica) from the French framboise, meaning "raspberry."
  • Other older names for yaws include granuloma tropicum, polypapilloma tropicum, and thymiosis.

What are developmental stages in the course of yaws?

  • Yaws has four stages: primary, secondary, latent, and tertiary.
  • The primary stage is the appearance of the mother yaw. Patients with yaws develop recurring ("secondary") lesions and more swollen lymph nodes. This represents the secondary stage.
  • These secondary lesions with rashes may be painless like the mother yaw or they may be filled with pus, burst, and form ulcers. The affected child often experiences malaise (feels poorly) and anorexia (loss of appetite).
  • The latent stage occurs when the disease symptoms abate, although an occasional lesion may occur.
  • In the tertiary stage, yaws can destroy areas of the skin, bones, and joints and deform them with pains in the joints and/or bones. The palms of the hands and soles of the feet tend to become thickened and painful (crab yaws).

What types of specialists treat yaws?

  • Usually, clinics or traveling doctors treat yaws because the populations that get the disease are usually the poor who have no medical care.
  • However, specialists like infectious-disease doctors, travel-medicine specialists, rheumatologists, dermatologists and others, depending on the extent of the disease, may be consulted if the patient is treated in more modern facilities.

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How is yaws diagnosed?

  • Yaws is suspected in any child who has the characteristic clinical features and lives in an area where the disease is common. With increasing travel, a child once in the tropics may carry the disease to a more temperate area of the world.
  • Laboratory confirmation of the diagnosis is by blood serum tests (for example, RPR or rapid plasma reagent test, VDRL test or venereal disease research laboratory test, TPHA or Treponema pallidum hemagglutination test, FTA-ABS or fluorescent treponema antibody absorption), but most frequently the diagnosis is made on clinical findings.
  • The reason that T. pallidum serum tests are used is that the spirochetes are so closely related, they have similar antigens on their surfaces so that T. pallidum and T. pertenue are cross-reactive (detected by the same serological tests). Special (dark-field) examination under the microscope in which technicians can actually see the spirochete bacterium is also used to help diagnose yaws.
  • The lesions (both the mother yaw and the secondary lesions) usually have many T. pertenue organisms that can be visualized with dark-field examination of lesion scrapings.
  • On a typical Gram stain (a procedure for identifying bacteria when viewed microscopically), the organisms are considered to be Gram-negative but stain so poorly and are so small and thin, the Gram stain often does not reveal the organisms; hence the use of the dark-field examination.
  • Other tests that detect spirochetes such as a silver stain or electron microscopy are used mainly by research scientists. PCR tests can confirm yaws by detecting genetic material from organisms in samples from skin lesions.

What is the treatment for yaws?

  • Treatment of yaws is simple and highly effective. Penicillin G benzathine given IM (intramuscularly) can cure the disease in the primary, secondary, and usually in the latent phase.
  • Penicillin V can be given orally for about seven to 10 days, but this route is less reliable than direct injection. Anyone allergic to penicillin can be treated with another antibiotic, usually erythromycin, doxycycline, or tetracycline.
  • Azithromycin (in a single oral dose of 30 mg/kg or the maximum 2 g) is the choice that the World Health Organization (WHO) recommends because of the ease of administration.
  • Tertiary yaws, which occurs in about 10% of untreated patients five to 10 years after initially getting the disease, is not contagious. The tertiary yaws patient is treated for the symptoms of the chronic conditions (altered or destroyed areas in bones, joints, cartilage, and soft tissues) that develop as complications of the infection.
  • There is no vaccine for yaws.

Why is yaws a serious problem?

  • Yaws is a major public-health threat in the tropics. Tropical regions in Central and South America, Africa, Asia, and Oceania are all at continuing risk for yaws.
  • A high percentage of children in such areas can be infected. Transmission of the disease is facilitated by overcrowding and poor hygiene, and yaws tends to be more prevalent in poor areas. In addition to making young children sick, approximately 10% of untreated children develop into young adults with deformities that are severely debilitating in the tertiary-yaws phase. For example, some patients develop destructive ulcerations of the nasopharynx, palate and nose (termed gangosa), painful skeletal deformities, especially in the legs (termed saber shins), and other soft-tissue changes (gummas, inflammatory cell infiltration).
  • Yaws can be completely eradicated from an area by giving penicillin or other appropriate antibiotics to everyone in the population. This may, unfortunately, cost more than a poor country can afford.
  • From 1950-1970, a worldwide effort to eradicate yaws was begun and made progress in reducing the approximately 50 million worldwide cases; after its end, yaws has seen a resurgence.
  • In the 1990s, attempts to eliminate yaws started again, with limited success as the effort is not worldwide or coordinated but done by individual countries. The WHO (World Health Organization) in 2007 reported about 2.5 million cases worldwide but freely admits their data is faulty, as most countries do not calculate the prevalence of yaws.
  • WHO estimates that about 460,000 new cases of yaws occur each year.

What is the prognosis of yaws?

  • The prognosis of yaws depends upon effective treatment so that the patient will not develop complications.
  • If appropriate treatment of yaws takes place before tertiary yaws develops, the prognosis for a possible cure with little or no complications is good. However, if tertiary yaws develops, the prognosis is worsened depending upon the severity of complications.

Is it possible to prevent yaws?

  • There is no vaccine available to prevent yaws. However, the WHO has established a yaws eradication strategy also referred to as the Morges strategy by which the organization has established a goal of eradicating yaws by about 2020. Because this disease is spread by person-to-person transfer and has no animal reservoir, the WHO considers this a realistic goal.
  • Currently, for individuals, prevention is based on interrupting the transmission of the disease from person to person by practicing good hygiene and by early diagnosis and rapid appropriate treatment with azithromycin to prevent spread in the community.

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Medically Reviewed on 8/5/2021
References
Switzerland. World Health Organization. "Yaws." June 2016. <http://www.who.int/mediacentre/factsheets/fs316/en/>.
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