Yaws, also known as pian or frambesia tropica, is an infectious disease, transmitted by non-venereal contact, caused by treponema pertenue. The main clinical manifestations are painful skin papules, ulcers, scabs, and various systemic symptoms. Destructive changes in bone may occur in late stage in children, which can sometimes cause painful lesions of the skin and bone. Unlike syphilis, yaws does not have mother-to-child transmission.
The pathogen is treponema pertenue, a subspecies of treponema pallidu
The source of infection is mainly patients with yaws. Healthy individuals can be infected after breaches of skin are in contact with exudate containing treponema pertenue. It has been reported that flies may transmit the pathogen. Treponema pertenue enters the human body by directly contacting the wounded skin, but not transmitted by sexual activity, so yaws is not a sexually transmitted disease.
Spirochetes enter the blood circulation and cause damage to bones, lymph nodes, and skin. The disease is mainly characterized by skin involvement. The heart and central nervous system are not involved, and there are no congenital infections.
The main pathological feature of yaws is skin lesions. Treponema pertenue enters blood from wounded skin, which is similar to syphilis but slower, involving bones, lymph nodes, and skin. Early lesions are characterized by thickened epidermis, dermal cell infiltration, hyperplasia, edema, and microabscesses, large amounts of treponema pertenue in the stratum spinosum, papillary hyperplasia, papillary interstitial thickening, epithelial hyperkeratosis, and epidermal ulcers with dried exudate. Diffuse periostitis and osteoporosis of long bones can be seen in the early stage, while endometritis, ulcerative granulomatous nodules, and gummas can be visible in the late stage. Skeletal lesions can cause extensive deformities.
Signs and Symptoms
The disease mainly affects children, more common in school-age children.
The incubation period is about 3 - 4 weeks, and the clinical duration is divided into three stages.
The stage is also known as mother yaws stage. A single, flat or hemispherical, bulging papule occurs at the infected site after the incubation period, gradually enlarging, up to 2 - 5 cm in diameter. The skin lesion is covered by yellowish brown, thin or thick crusts, and pale red, strawberry granulation can be seen after the crusts are removed, containing large amounts of treponema pertenue, which is the primary eruption, termed mother yaws. Non-specific treponema pallidum agglutination test is positive appropriately 2 weeks after the occurrence of mother yaws. The mother yaws is surrounded by some satellite yaws, mostly in the extremities and face. However, children with yaws can spread the disease to mother's breast and torso. Subjective pruritus and local lymphadenopathy are present, but tenderness is absent. The mother yaws subsides spontaneously in months, leaving mild atrophy and depigmentation.
The stage is also known as yaws eruption stage. The illness progresses into secondary stage several weeks to months after the occurrence of mother yaws. Numerous, small eruptions similar to mother yaws occur mostly on the face and limbs. Initial skin lesions are smooth, and with the increase of secretions, yellowish brown crusts develop, which are oyster shell shaped after thickening.
The rashes can also be clustered. Central rashes subside, leaving pigmentation, and peripheral rashes are arranged annularly, which are termed ringworm yaws. The rashes in the cubital fossa, perianal area, and groin area present with pale red, strawberry granulation after exfoliation of crusts, with large amounts of secretions, resembling condyloma latum. Verrucous lesions are common in the dorsal feet, and the rashes of eyelids are crusty. The miliary rash occurs mostly on the shoulder, resembling lichen scrofulosorum, which is termed lichen frambesianus. Local lymph nodes are enlarged but not purulent. The yaws rashes can regress spontaneously in few weeks or months, leaving pigmentation or no traces.
The stage is also known as ulcer and nodule stage. Most patients are healing at the secondary stage, but the illness may progress into tertiary stage 5 - 10 years after infection. The rashes resemble gummas in syphilis. Sharply edged or undermined, painless ulcers occur and extend peripherally, and may be linear or creeping, with protracted duration. Treponema pertenue cannot be found in the secretions. Atrophic scar with depigmentation remains after ulcers heal. In addition, diffuse or punctate palmoplantar hyperkeratosis may occur, with fissures or depression, forming typical mottlings, mostly in the soles. Gummas may occur in the tibia and other long bones. Bone lesions include periostitis, saber shin, osteoporosis, and even void formation. Occasionally, nasal bone destruction and palatal perforation may be seen. Single or multiple juxtaarticular nodules can occur near the elbow, knee, and hip joints. The prognosis of tertiary yaws is better than that of syphilis, but deformity and disfigurement usually remain after healing.
The histopathology of primary and secondary yaws is inflammatory granulomatous lesions. The epidermal ridges and papillae widen and extend downwards, acanthosis is present, and large amounts of neutrophils invade the epidermis, forming microabscesses. Dermal lymphocytes and plasma cells infiltration are seen. Vasodilation is present, but changes in the vessel wall is less common. Spirochetes are mainly found in the epidermal stratum spinosum, and also in the stratum papillare.
In the tertiary yaws, dermal epithelioid cells, mononuclear cells, and plasma cells infiltration are present. Necrosis can be seen in the late stage, and giant cells often appear, but the vessel wall changes are less common.
The diagnostic considerations include patients in the epidemic area, adolescents or children, skin lesions in the exposed area, usually a mother yaws similar to strawberry after exfoliation of crusts, pathogen found in dark field microscopy, and positive treponema pallidum agglutination test 1 - 2 months after onset.
The treatment regimen is benzathine penicillin 1,200,000U intramuscularly in adults, 600,000U intramuscularly in children with body weight less than 45kg, in single dose. Those who are allergic to penicillin can use azithromycin 30 mg / kg (maximally 2 g) orally in single dose or doxycycline 100 mg orally twice daily for 14 days.
Early diagnosis and prompt treatment can contribute to a good prognosis. Periodic relapses and protracted duration may be present, but sometimes spontaneous healing can be seen.
This disease is a contagious disease, so contact with patients with yaws should be avoided, and skin trauma and insect bites can be prevented.