What is yaws?
Yaws is a chronic tropical skin infection that may also infect bones in its late stages.
Yaws is caused by a spiral-shaped bacterium (spiroch(a)ete), Treponema pallidum pertenue. Yaws belongs to the same family of bacteria as syphilis, Treponema pallidum pallidum.
Yaws may be locally known as pian, parangi, paru, patek, buoba, coko and tona.
How common is yaws?
Yaws was nearly eradicated by a worldwide treatment program in the 1950-60s. Between 1959-1961, people from Fiji, Samoa, Tonga, Cook Islands and Tokelau Islands were given injections of penicillin as part of a World Health Organisation (WHO) campaign.
However, a 2007 WHO report suggests yaws is on the rise again, mostly in poor, rural areas of West and Central Africa, Southeast Asia (Indonesia), and some Pacific Islands, such as Papua New Guinea and the Solomon Islands.
Who is at risk of yaws and how is it spread?
Yaws affects young children under 15 years of age. It occurs mainly in warm, humid, tropical areas of Africa, Southeast Asia, South America, and Oceania among poor rural populations living in overcrowded conditions.
Yaws is spread from person to person through direct contact with infectious ulcers. The bacteria enter the skin at sites of trauma such as scratches and bites on the legs.
What are the signs and symptoms of yaws?
Yaws is characterised by four distinct stages.
Laboratory tests for yaws
Yaws is usually diagnosed on the clinical findings of characteristic skin changes because T pallidum pertenue cannot be distinguished from T pallidum pallidum or other treponemal subspecies with commercially available laboratory tests. Other tests such as PCR are not yet routinely available.
Spirochetes may be detected during the primary or secondary infectious stages by dark-field microscopic examination of tissue or tissue fluid taken from a papule, ulcer or lymph node.
There are two important blood tests:
- Non-treponemal tests (e.g. RPR, VDRL): these are usually positive in all stages of infection, except very early lesions.
- Specific anti-treponemal antibody tests (e.g. TPHA, EIA): these detect antibody due to past or present infection with any treponeme. They cannot distinguish between yaws or syphilis or indicate the duration of infection. Most people with reactive treponemal tests will continue to have reactive tests for the remainder of their lives, regardless of treatment or disease activity.
What does a positive syphilis test mean?
Blood tests are often done for syphilis as part of antenatal screening, an immigration medical, or as a workup for undiagnosed health problems. It can be difficult to work out the exact cause for a positive result.
Positive syphilis test results may be due to current or past infection with any treponeme, as the same antibody is produced in response to yaws, syphilis and a less common infection, pinta.
Because of the potentially severe consequences of late syphilis infection, it is prudent to assume anyone born after 1960 has syphilis and to treat accordingly, unless there is clear documentation suggesting otherwise.
What is the treatment for yaws?
If appropriately treated in its early stages, yaws is highly curable. A single injection of long-acting penicillin into a muscle is effective.
Skin lesions may take several months to heal. If treated in its late stage, significant disfigurement may persist permanently.