Evaluation of a Rapid Dual Point-of-care Assay for Targeting Antibiotic Treatment for Yaws Eradication: a Prospective Descriptive Study

Yaws is an infectious disease caused by Treponema pallidum subspecies pertenue, a bacterium which closely resembles the causative agent of syphilis, and is spread by skin to skin contact. In the field, yaws is diagnosed on the basis of epidemiological context, evocative symptoms and signs and positive serological tests or dark field microscopy. The darkfield microscopy is not easy to perform , hence the interest in serological tests. The serological tests used to confirm yaws are the same as those used to diagnose syphilis. Yaws serologic diagnosis relies on testing for non-treponemal and treponemal antibodies. These antibodies differ markedly with respect to antigenic reactivities and kinetics during the disease process.

Historically screening for yaws has involved the use of nontreponemal tests, such as rapid plasma reagin or venereal disease research laboratory. Positive results of nontreponemal tests of specimens are then confirmed using a more specific treponemal test, such as Treponema pallidum haemagglutination. However, the equipment and personnel requirements for conducting and interpreting these laboratory-tests are rarely available in low-resource settings in developing countries where yaws occurs.

Rapid treponemal tests which detect antibodies to T. pallidum antigen have become popular for the diagnosis of venereal syphilis due to their many advantages. These tests that can be performed outside a laboratory setting with minimal training and using blood collected by a finger prick, which makes them extremely useful in remote areas where laboratories are not available. However, the rapid treponemal tests for syphilis detect treponemal antibodies, which limits their use for interpretation of the disease status since they cannot distinguish between active and past or treated infection.

A combined point-of-care (POC) test which detects both treponemal and non-treponemal antibodies has recently been evaluated for the diagnosis of syphilis, and appears promising for yaws diagnosis. The use of the dual POC test would result in the ability to both screen and confirm the serological status of patients with suspected yaws within 15 minutes and give a better indication of active disease.