Yaws is a tropical infection of the skin, bones and joints caused by the spirochete bacterium Treponema pallidum pertenue. The disease begins with a round, hard swelling of the skin, 2 to 5 centimeters in diameter.The center may break open and form an ulcer.This initial skin lesion typically heals after three to six months.After weeks to years, joints and bones may become painful, fatigue may develop, and new skin lesions may appear.
The skin of the palms of the hands and the soles of the feet may become thick and break open. The bones (especially those of the nose) may become misshapen. After five years or more large areas of skin may die, leaving a scar.
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. The disease 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. 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, diseases caused by spiral bacteria in the genus Treponema; besides yaws, the disease include endemic syphilis (bejel) and pinta. Of these three diseases, yaws is the most common.
Yaws is spread by direct contact with the fluid from a lesion of an infected person. The contact is usually of a non-sexual nature. The disease is most common among children, who spread it by playing together.Other related treponemal diseases are bejel (Treponema pallidum endemicum), pinta (Treponema pallidum carateum), and syphilis (Treponema pallidum pallidum). Yaws is often diagnosed by the appearance of the lesions. Blood antibody tests may be useful but cannot separate previous from current infections. Polymerase chain reaction (PCR) is the most accurate method of diagnosis.
Yaws, also called frambesia, contagious disease occurring in moist tropical regions throughout the world. It is caused by a spirochete, Treponema pertenue, that is structurally indistinguishable from T. pallidum, which causes syphilis. Some syphilologists contend that yaws is merely a tropical rural form of syphilis, but yaws is not contracted primarily through sexual activity, and later systemic complications from the disease are much rarer than in syphilis.
The Wassermann and Kahn tests for syphilis, however, often read positive with yaws, and there is some degree of cross-immunity. The spirochetes of yaws are present in the discharge from lesions on the skin and are transferred by direct contact to the abraded skin of an uninfected person; by contaminated clothing; and by flies that feed on the sores. The disease is most frequently contracted in early childhood, and considerable immunity to subsequent infection is acquired.
Prevention is, in part, by curing those who have the disease thereby decreasing the risk of transmission. Where the disease is common, treating the entire community is effective. Improving cleanliness and sanitation will also decrease spread. Treatment is typically with antibiotics including: azithromycin by mouth or benzathine penicillin by injection. Without treatment, physical deformities occur in 10% of cases.
Yaws is common in at least 14 tropical countries as of 2012. The disease only infects humans. In the 1950s and 1960s the World Health Organization (WHO) nearly eradicated yaws. Since then the number of cases has increased and there are renewed efforts to globally eradicate the disease by 2020. The last estimate of the number of people infected was more than 500,000 in 1995. Although one of the first descriptions of the disease was made in 1679 by Willem Piso, archaeological evidence suggests that yaws may have been present among humans as far back as 1.6 million years ago.
Yaws is an infectious tropical disease caused by the spirochete (spiral shaped) bacterium known as Treponema pertenue. The disease presents in three stages of which the first and second are easily treated. The third, however, may involve complex changes to the bones in many parts of the body. The first stage is characterized by the appearance of small, painless bumps on the skin that group together and grow until they resemble a strawberry. The skin may break open, forming an ulcer.
The second stage (usually starting several weeks or months after the first) presents with a crispy, crunchy rash that may cover arms, legs, buttocks and/or face. If the bottoms of the feet are involved, walking is painful and the stage is known as “crab yaws.” Stage 3 yaws involves the long bones, joints, and/or skin. Yaws is very common in tropical areas of the world but it is not known in the United States. It is not a sexually transmitted disease. It occurs in children younger than 15 years of age.
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.
- pallidum pertenuehas 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
Yaws is an infectious disease caused by a spiral-shaped bacterium (spirochete) known as Treponema pertenue. Yaws is usually transmitted by direct contact with the infected skin sores of affected individuals. In some cases, yaws may be transmitted through the bite of an infected insect.
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.
Signs and symptoms
Within 90 days (but usually less than a month) of infection a painless but distinctive “mother yaw” nodule appears, which enlarges and becomes warty in appearance. Nearby “daughter yaws” may also appear simultaneously.
This primary stage resolves completely within six months. The secondary stage occurs months to years later, with typically widespread skin lesions that vary in appearance, including “crab yaws” on the palms of the hands and soles of the feet with desquamation. These secondary lesions frequently ulcerate and are then highly infectious, but heal after six months or more. About 10% of people then go on to develop tertiary disease within five to ten years (during which further secondary lesions may come and go), with widespread bone, joint and soft tissue destruction, which may include extensive destruction of the bone and cartilage of the nose (Rhinopharyngitis mutilans or “gangosa”).
Stage 1 yaws typically occurs in early childhood, with peak incidence at about six years of age. A single itchy, strawberry-like growth appears on the skin over which a thin yellow crust forms (papillomatous lesion). This growth, the “mother yaw”, appears at the spot where the organism entered the body (inoculation site), typically on the leg or foot.
Stage 2 yaws typically follows several weeks or months after the initial symptoms. Similar skin sores appear on the face, legs, arms, and/or around the rectum and genitals. These sores usually heal slowly and may recur. Lesions on the bottom of the feet may produce painful cracks and ulcerations (keratosis), resulting in an awkward “crab-like” walk or “crab yaws.”
At this stage, swollen glands (swollen lymph nodes) are not uncommon and the rash may develop a brown crust.
The symptoms of stage 3 yaws occur in only about 10% of the people who are infected and may follow a dormant period of several years. Painful ulcers or nodules may develop on the skin (cutaneous) and cause facial disfigurement. Painful, granular sores (gummatous lesions) may also develop on the bones, especially the long bones of the legs (tibia). Painful skin and bone nodules may impair joint function and mobility.
Stage 3 yaws may also produce different and distinct syndromes. One, known as goundou syndrome, is characterized by inflammation and swelling of the tissues surrounding the nose (paranasal swelling), as well as overgrowth of the bones in the same region of the face (hypertrophic osteitis). Another, known as gangosa syndrome (also known as rhinopharyngitis mutilans), is characterized by degenerative changes of the nose, throat (pharynx), and the roof of the mouth (hard palate).
There are two basic stages of yaws disease – early (infectious) and late (non-infectious):
- In early yaws, an initial papule develops at the site of entry of the causative organism. This papule is full of the organisms and may persist for 3-6 months followed by natural healing. Without treatment, this is followed by disseminated skin lesions over the body. Bone pain and bone lesions may also occur.
- Late yaws appears after five years of the initial infection and is characterized by disabling consequences of the nose, bones and palmar/plantar hyperkeratosis.
In the field, diagnosis is primarily based on clinical and epidemiological findings:
A person (75% are children below 15 years) who lives in an endemic area and presents with one or more of the following signs:
- painless ulcer with scab
- palmar/plantar hyperkeratosis (thickening).
The clinical diagnosis can be confirmed by examining a sample from a skin lesion under a special type of microscope (darkfield examination). There is no specific blood test for yaws, but because it is closely related to the bacterium that causes syphilis, the blood tests for syphilis are diagnostic in yaws as well.
The diagnosis of stage 1 and stage 2 yaws is made by microscopic examination of tissue samples (darkfield examination) from the skin lesions of affected individuals. Stage 3 yaws may be diagnosed by specialized blood tests (i.e., VDRL and treponemal antibodies).
Traditionally, laboratory-based serological tests such as Treponema pallidum particle agglutination (TPPA) and rapid plasma reagin (RPR) are widely used to diagnose treponemal infections (for example, syphilis and yaws). These tests cannot distinguish yaws from syphilis however, and the interpretation of results from these tests in adults who live in yaws endemic areas therefore needs careful clinical assessment.
Rapid point-of-care (3) tests that can be used in the field are widely available. However, most of them are treponemal-based and cannot distinguish between past and current infection. Recently dual treponemal and nontreponemal rapid tests have become available, thus simplifying diagnosis in the field. These tests are able to detect both present and past infections so as to guide immediate treatment.
Polymerase chain reaction (PCR) technology is used to definitively confirm yaws by detecting the organisms in the skin lesions (4). It can also be used to monitor azithromycin resistance. The application of PCR in yaws eradication will be very useful after mass treatment when the few cases that occur must be proven to be yaws.
Stage 1 and 2 yaws is treated with antibiotics, especially with benzathine penicillin G. A single large dose of these medications usually heals the skin lesions and eliminates the organism. These antibiotic drugs may also be used to prevent this disease in family members and others who are in frequent contact with affected individuals. At the present time, there is no treatment for the destructive bone lesions or scars associated with stage 3 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.
Either of 2 antibiotics – azithromycin or benzathine penicillin – may be used to treat yaws:
- Azithromycin (single oral dose) at 30 mg/kg (maximum 2 g) is the preferred choice in the WHO “Yaws Eradication Strategy” (the Morges Strategy) because of the ease of administration and logistical consideration in large-scale treatment campaigns.
- Benzathine penicillin (single intramuscular dose) at 0.6 million units (children aged under 10 years) and 1.2 million units (people aged over 10 years) for patients who “clinically fail on azithromycin”, or are allergic to azithromycin.
There is no vaccine for yaws. Prevention is based on the interruption of transmission through early diagnosis and treatment of individual cases and mass or targeted treatment of affected populations or communities. Health education and improvement in personal hygiene are essential components of prevention.
There is no vaccine to prevent Yaws. The principles of prevention are based on the interruption of transmission by early diagnosis and treatment of affected individuals and their contacts.
It is currently thought that it may be possible to eradicate yaws although it is not certain that humans are 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 believed to be highly localised.
In April 2012, WHO initiated a new global campaign for the eradication of yaws, which has been on the WHO eradication list since 2011. According to the official roadmap, elimination should be achieved by 2020.
Prior to the most recent WHO campaign, India launched its own national yaws elimination campaign which appears to have been successful.
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 was 46. The last clinical case in India was reported in 2003 and the last latent case in 2006. India is a country where yaws is now considered to have been eliminated
In March 2013, WHO convened a new meeting of yaws experts in Geneva to further discuss the strategy of the new eradication campaign. The meeting was significant, and representatives of most countries where yaws is 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.
Past efforts to control yaws
Of the 13 countries known to be currently endemic with yaws, 8 of them reported more than 46 000 cases in 2015. Further assessment is needed to ascertain endemicity in the 5 other countries. Recent estimates indicate that about 89 million people live in the 13 countries endemic for yaws (1). Out of the countries known to have been endemic in the 1950s, at least 73 need to be assessed to determine interruption of transmission so that WHO can take steps to certify them free of the disease as part of the global eradication process.
In May 2016, WHO declared India free of yaws. Although Ecuador has reported no cases for several years, it has not yet been verified as free of yaws.
- Between 1950 and 1970, WHO and UNICEF led a worldwide campaign to control yaws in 46 countries.
- Mass campaigns using mobile teams in all 46 countries led to the treatment of 50 million people and by 1970, the prevalence of the disease had decreased by 95%.
- Consequently but unfortunately, in the 1970s the vertical programmes in many countries were dismantled and yaws activities were integrated into the primary health care system to deal with the “last cases”. Resources, attention and commitment for yaws activities gradually disappeared.
- By the late 1970s, the disease had began to creep back, resulting in a World Health Assembly Resolution (WHA 31.58) in 1978.
- Renewed control efforts were attempted in many countries (particularly in West Africa) in the early 1980s, but these attempts failed after a few years because of lack of political will and resources.
- Since 1995, there have been renewed elimination efforts in some regions and countries but there is no global coordination.
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 another 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.
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. Because T. pallidum pertenue is temperature- and humidity-dependent, yaws is found in humid tropical regions in South America, Africa, Asia and Oceania.
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.
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 the 1970s with the largest number of case found in the Western Africa region.
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