10.1.5 Yaws

None.

Most commonly seen among children children between 2 to 15 years of age (reservoirs for the spirochete) in endemic tropical regions with warm and humid environments. Infection is spread by direct skin to skin contact. Since the annual incidence fell dramatically over the past years, there is hope that the disease will be eradicated. Poor hygiene, poverty, crowding, rural settings, and a climate of heavy rainfall and high humidity are risk factors for transmission.

Non-venereal tropical infectious disease caused by Treponema pertenue, which is closely related to the syphilitic spirochete, Treponema pallidum.

Unlike syphilis, yaws is neither sexually transmitted nor transmitted from mother to baby. Disease is most commonly seen in children and is transmitted from skin to skin, and possibly by fly vectors; there is no evidence of zoonotic transmission.

Three clinical stages, similar to syphilis: early stage with cutaneous lesions; latent period; gummatous nodules, scarring, and destructive osteitis in late stage .

The initial stage (“Mother Yaw” )at the site of inoculation on average 9-90 (21) days after exposure: solitary nodules or multiple ulcerative non-tender exudative papules, 2 to 5 cm in diameter, showing  a distinct red base of granulation tissue with elevated borders, that may degenerate into a single crusted non-tender ulcer. Untreated lesions heal spontaneously over 3 to 6 months leaving hyperpigmentation.

Second stage (“crab-yaws”) (2 months up to 2 years after inoculation; may overlap with the initial stage): Lymphatic or hematogenous spread of the organism with progression of the disease. Symptoms include arthralgias, disseminated papillomatous or ulcerative lesions with macular or hyperkeratotic palmoplantar involvement with painful fissuring and secondary infection, generalized lymphadenopathy and osteoperiostitis (most frequently radius, ulna, and phalanges).

Latent period: Between primary and secondary and tertiary stages, without clinical signs but positive serology.

Tertiary disease (5 to 10 years after inoculation): In 10% of untreated patients. Symptoms are ulcerative necrotic nodules, leading to facial destruction, and juxtaarticular nodules (gummas), bowed tibia (saber shins), nasal cartilage destruction (gangosa), or exostosis of the paranasal maxilla (gondou).

The most common location is the lower extremity, but any site of exposure may be involved.

The most common location is the lower extremity, but any site of exposure may be involved.

T. pertenue belongs to the group of uncultivable spirochete. They are not viable ex vivo, and therefore, diagnostic methods are limited. Darkfield microscopy -which is not everywhere available- does allow direct visualization of spirochetes. Serologic assays and nucleic acid amplification tests have been used as the primary mode of identification.

In early yaws there is marked epidermal hyperplasia and papillomatosis, with focal spongiosis, neutrophilic microabscesses in the epidermis and plasma cells in the dermis, with  only little endothelial cell proliferation or vascular obliteration (in contrast to syphilis). With Warthin-Starry silver stains or polyclonal antibodies to T pallidum, the bacteria can be detected in the epidermis.

Slowly progressive through several stages if not treated.

Superinfection. Progression of the disease through latent stage, if not properly treated.

Diagnosis is based on the combined clinical picture and serologic testing (see also syphilis chapter 2.5.7)

Other treponemal diseases and tropical ulcers.

Benzathine penicillin-G, or single dose of azithromycin for primary and secondary stages.

There is a good chance to eradicate yaws in the near future.