Rapid Diagnostic Test Evaluated for Yaws Infection

Yaws is a non-venereal treponemal infection caused by a spirochete bacterium Treponema pallidum ssp. pertenue (T. pertenue) which is currently thought to be endemic in fourteen countries and the emergence of azithromycin as an effective oral agent in the treatment of yaws has prompted renewed calls for a coordinated worldwide program to eradicate the disease.

Scientists the London School of Hygiene & Tropical Medicine (UK) working with colleagues from the Solomon Islands evaluated the utility of a Dual Path Platform (DPP) test in screening for yaws, utilizing samples collected as part of a community prevalence survey conducted in the Solomon Islands. The sera from four hundred and fifteen samples were randomly selected. The median age was 9 years, and 52.1% of participants were male. Individuals selected for this study did not differ significantly from the larger prevalence survey population with regards to demographic or clinical features. Clinical findings consistent with active and healed yaws were found in 19 (4.7%) and 34 (8.2%) respectively of the 415 participants.

Sera were tested using traditional syphilis tests, the Treponema pallidum particle agglutination assay (TPPA, Mast Diagnostics; Merseyside, UK) and a quantitative Rapid Plasma Reagin assay (RPR, Deben Diagnostics; Sheffield, UK) and the new RDT, the DPP Syphilis Screen and Confirm (Chembio; Medford, NY, USA). The investigators found 123 (29.6%) individuals had a reactive TPPA and120 (28.9%) individuals had a reactive RPR at any titer. By gold standard serology there were 18 individuals with a false positive RPR, defined as a positive RPR and negative TPPA. All false positive RPRs in the study had an RPR titer of 1:2. The overall prevalence of true RPR reactivity was therefore 102/415 (24.6%). The sensitivity of the DPP was strongly related to the RPR titer with a sensitivity of 92.0% for an RPR titer of greater than 1:16.

The authors concluded that the DPP test can be used as part of a community surveillance strategy to identify individuals who are dually seropositive with high-titer RPRs. These individuals are most likely to represent the major source of ongoing transmission. Wider access to DPP testing would improve the awareness of worldwide yaws case reporting and the test may play a key role in assessing patients presenting with yaws like lesions in a post-mass drug administration (MDA) setting. The study was published on September 11, 2014, in the journal Public Library of Science Neglected Tropical Diseases.

Related Links:
London School of Hygiene & Tropical Medicine 
Mast Diagnostics 
Deben Diagnostics