How do health-care professionals diagnose yaws?
Yaws is suspected in any child who has the characteristic clinical features and lives in an area where the disease is common. With increasing travel, a child once in the tropics may carry the disease to a more temperate area of the world.
Laboratory confirmation of the diagnosis is by blood serum tests (for example, RPR or rapid plasma reagent test, VDRL test or venereal disease research laboratory test, TPHA or Treponema pallidum hemagglutination test, FTA-ABS or fluorescent treponema antibody absorption), but most frequently the diagnosis is made on clinical findings. The reason that T. pallidum serum tests are used is that the spirochetes are so closely related, they have similar antigens on their surfaces so that T. pallidum and T. pertenue are cross-reactive (detected by the same serological tests). Special (dark-field) examination under the microscope in which technicians can actually see the spirochete bacterium is also used to help diagnose yaws. The lesions (both the mother yaw and the secondary lesions) usually have many T. pertenue organisms that can be visualized with dark-field examination of lesion scrapings. On a typical Gram stain (a procedure for identifying bacteria when viewed microscopically), the organisms are considered to be Gram-negative but stain so poorly and are so small and thin, the Gram stain often does not reveal the organisms; hence the use of the dark-field examination. Other tests that detect spirochetes such as a silver stain or electron microscopy are used mainly by research scientists. PCR tests can confirm yaws by detecting genetic material from organisms in samples from skin lesions.