yaws yaws 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 cm (0.79 to 1.97 in) in diameter. the center may break open and form an ulcer. this initial skin lesion typically heals after 3–6 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 5 years or more, large areas of skin may die, leaving scars. yawsother namesframbesia tropica, thymosis, polypapilloma tropicum, non-venereal endemic syphilis, parangi and paru (malay), bouba (spanish), frambösie, pian (french), frambesia (german), bakataw (maguindanaoan)nodules on the elbow resulting from a treponema pallidum pertenue bacterial infectionspecialtyinfectious diseasesymptomshard swelling of the skin, ulcer, joint and bone paincausestreponema pallidum pertenue spread by direct contactdiagnostic methodbased on symptoms, blood antibody tests, polymerase chain reactionpreventionmass treatmentmedicationazithromycin, benzathine penicillinfrequency46,000–500,000 yaws is spread by direct contact with the fluid from a lesion of an infected person. the contact is usually of a nonsexual nature. the disease is most common among children, who spread it by playing together. other related treponemal diseases are bejel (t. pallidum endemicum), pinta (t. carateum), and syphilis (t. p. 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 is the most accurate method of diagnosis. no vaccine has yet been found. prevention is, in part, done 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 also decreases 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 13 tropical countries as of 2012. almost 85% of infections occurred in three countries—ghana, papua new guinea, and solomon islands. the disease only infects humans, although 18th century french historian pierre françois xavier de charlevoix describes it as a disease among geese in the antilles. efforts in the 1950s and 1960s by the world health organization decreased the number of cases by 95%. since then, cases have increased, but with renewed efforts to globally eradicate the disease by 2020. in 1995, the number of people infected was estimated at more than 500,000. in 2016, the number of reported cases was 59,000. 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 human ancestors as far back as 1.6 million years ago. signs and symptoms yaws is classified as primary, secondary, and tertiary; this is useful, but people often have a mix of stages. within 9–90 days (but usually about 21 days) of infection, a painless but distinctive "mother yaw" nodule appears. initially reddened and inflamed, it may become a papilloma, which can then become an ulcer, possibly with a yellow crust. mother yaws are most commonly found on the legs and ankles, and are rarely found on the genitals (unlike syphilis) the mother yaw enlarges and becomes warty in appearance. nearby "daughter yaws" may also appear simultaneously. this primary stage resolves completely, with scarring, within 3–6 months. the scar is often pigmented. papilloma mother yaw mother yaw nodule with central ulceration and a yellow crust ulcerated mother yaw ulcerated mother yaw healed primary yaw lesion, showing pigmented scar the secondary stage occurs months to two years later (but usually 1–2 months later), and may thus begin when the mother yaw has not yet healed. it happens when the bacterium spreads in the blood and lymph. it begins as multiple, pinhead-like papules; these initial lesions grow and change in appearance and may last weeks before healing, with or without scarring. secondary yaws typically shows widespread skin lesions that vary in appearance, including "crab yaws" (areas of skin of abnormal colour) on the palms of the hands and soles of the feet (named for the crab-like gait they cause people with painful soles to assume). these may show desquamation. these secondary lesions frequently ulcerate and are then highly infectious, but heal after 6 months or more. secondary yaws affects the skin and bones. the most common bone-related problem is periostitis, an inflammation around the bone, often occurs in the bones of the fingers and the long bones of the lower arms and legs, causing swollen fingers and limbs. this causes pain at night and thickening of the affected bones (periostitis). about 75% of infected children surveyed in papua new guinea reported joint pain. swollen lymph nodes, fever, and malaise are also common. after primary and secondary yaws (and possibly, in some cases, without these phases), a latent infection develops. within five years (rarely, within ten years) it can relapse and become active again, causing further secondary lesions, which may infect others. these relapse lesions are most commonly found around the armpits, mouth, and anus. secondary yaws begin as multiple small lesions. the small lesions grow. secondary lesions vary in appearance (see list of terms) here two different appearances (papulosquamous plaque and yellow-crusted nodules) are seen in the same 10-year-old person (large-scale of both, close-up of nodules) hypopigmentation and an crusted erosion, elbow of a 5-year-old secondary yaws; hypopigmented areas of skin topped with pink and brown papules, 9-year-old erosion on the sole of the foot, close-up (large-scale). if deeper, it would be an ulcer secondary yaws papilloma (same 9-year-old as pictures of feet) secondary breakout in a javanese child age of 12 years. wax model secondary yaws scars in an adult with childhood history of yaws an estimated 10% of people with yaws formerly were thought to develop tertiary disease symptoms, but more recently, tertiary yaws has been less frequently reported. tertiary yaws can include gummatous nodules. it most commonly affects the skin. the skin of the palms and soles may thicken (hyperkeratosis). nodules ulcerating near joints can cause tissue death. periostitis can be much more severe. the shinbones may become bowed (saber shin) from chronic periostitis. yaws may or may not have cardiovascular or neurological effects; definitive evidence is lacking. rhinopharyngitis mutilans rhinopharyngitis mutilans, also known as gangosa, is a destructive ulcerative condition that usually originates about the soft palate and spreads into the hard palate, nasopharynx, and nose, resulting in mutilating cicatrices, and outward to the face, eroding intervening bone, cartilage, and soft tissues. it occurs in late stages of yaws, usually 5 to 10 years after first symptoms of infection. this is now rare. very rarely, yaws may cause bone spurs in the upper jaw near the nose (gondou); gondou was rare even when yaws was a common disease. deep ulceration occurs in tertiary yaws severe tertiary yaws; gangosa goundu, a very rare yaws-caused deformity around the nose cause 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. early (primary and secondary) yaws lesions have a higher bacterial load, thus are more infectious. both papillomas and ulcers are infectious. infectivity is thought to last 12–18 months after infection, longer if a relapse occurs. early yaws lesions are often itchy, and more lesions may form along lines that are scratched. yaws may be evolving less conspicuous lesions. yaws is most common among children, who spread it by playing together. it is not thought to be transmitted from mother to child in the womb. yaws is not a venereal disease. t. pallidum pertenue has been identified in nonhuman primates (baboons, chimpanzees, and gorillas) and experimental inoculation of human beings with a simian isolate causes yaws-like disease. however, no evidence exists of cross-transmission between human beings and primates, but more research is needed to discount the possibility of a yaws animal reservoir in nonhuman primates. diagnosis lesion biopsy under a microscope, clear epidermal hyperplasia dactylitis of secondary yaws due to periostitisperiostitis of secondary yaws may be visible on an x-ray, even if not otherwise visible most often the diagnosis is made clinically. dark field microscopy of samples taken from early lesions (particularly ulcerative lesions) may show the responsible bacteria; the spirochaetes are only 0.3 µm wide by 6–20 µm long, so light-field microscopy does not suffice. a microscopic examination of a biopsy of a yaw may show skin with clear epidermal hyperplasia (a type of skin thickening) and papillomatosis (a type of surface irregularity), often with focal spongiosis (an accumulation of fluid in specific part of the epidermis). immune system cells, neutrophils and plasma cells, accumulate in the skin, in densities that may cause microabscesses. warthin–starry or levaditi silver stains selectively stain t. pallidum, and direct and indirect immunofluorescence and immunoperoxidase tests can detect polyclonal antibodies to t. pallidums. histology often shows some spatial features which distinguish yaws from syphilis (syphilis is more likely to be found in the dermis, not the epidermis, and shows more endothelial cell proliferation and vascular obliteration). blood-serum (serological) tests are increasingly done at the point of care. they include a growing range of treponemal and nontreponemal assays. treponemal tests are more specific, and are positive for any one who has ever been infected with yaws; they include the treponema pallidum particle agglutination assay. nontreponemal assays can be used to indicate the progress of an infection and a cure, and positive results weaken and may become negative after recovery, especially after a case treated early. they include the venereal disease research laboratory (vdrl; requires microscopy) and rapid plasma reagin (rpr; naked-eye result) tests, both of which flocculate patient-derived antibodies with antigens. serological tests cannot distinguish yaws from the closely related syphilis; no test distinguishing yaws from syphilis is widely available. the two genomes differ by about 0.2%. pcr and dna sequencing can distinguish the two. there are also no common blood tests which distinguish among the four treponematoses: syphilis (treponema pallidum pallidum), yaws (treponema pallidum pertenue), bejel (treponema pallidum endemicum), and pinta (treponema carateum). haemophilus ducreyi infections can cause skin conditions that mimic primary yaws. people infected with haemophilus ducreyi lesions may or may not also have latent yaws, and thus may or may not test positive on serological tests. this was discovered in the mid-2010s. it seems that a recently diverged strain of haemophilus ducreyi has evolved from being a sexually transmitted infection to being a skin ulcer pathogen that looks like yaws. yaws has been reported in nonendemic countries. treatment treatment is normally by a single intramuscular injection of long-acting benzathine benzylpenicillin, or less commonly by a course of other antibiotics, such as azithromycin or tetracycline tablets. penicillin has been the front-line treatment since at least the 1960s, but there is no solid evidence of the evolution of penicillin resistance in yaws. the historical strategy for the eradication of yaws (1952–1964) was: prevalence of clinically active yawstreatment strategy hyperendemic: above 10%benzathine benzylpenicillin to the whole community (total mass treatment) mesoendemic: 5–10%treat all active cases, all children under 15 and all contacts of infectious cases (juvenile mass treatment) hypoendemic: under 5%treat all active cases and all household and other contacts (selective mass treatment) benzathine benzylpenicillin requires a cold chain and staff who can inject it, and there is a small risk of anaphylaxis. it was also not reliably available during the 2010s; there have been supply shortages. in the 2010s, a single oral dose of azithromycin was shown to be as effective as intramuscular penicillin. unlike penicillin, there is strong evidence that yaws is evolving antibiotic resistance to azithromycin; there are two known mutations in the bacterium, each of which can cause resistance and make the treatment ineffective. this has threatened eradication efforts. within 8–10 hours of penicillin treatment, bacteria can no longer be found in lesion biopsies. primary and secondary lesions usually heal in 2–4 weeks; bone pain may improve within two days. if treated early enough, bone deformities may reverse and heal. primary and secondary stage lesions may heal completely, but the destructive changes of tertiary yaws are largely irreversible. if lesions do not heal, or rpr test results do not improve,