Methods for Detecting Syphilis Using Synthetic Antigens

Syphilis is a highly contagious sexually transmitted disease caused by the bacterium, Treponema pallidum (T. pallidum). If left untreated, syphilis can cause serious complications including blindness, paralysis and dementia.

The venereal disease research laboratory (VDRL) test is one type of screening test used to detect syphilis. This blood test first detects antibodies responding to antigens produced by cells damaged by Treponema pallidum bacteria. Note that some literature suggest that these antigens could also come from dead/dying T. pallidum cells. Due to the high incidence of false positive and false negative results, however, secondary confirmation of the test results must be done using an alternative, more specific assay. CDC and partner researchers developed a VDRL antigen using synthetic components (cardiolipin and lecithin) instead of native, purified components for improved detection of syphilis. The sensitivity has been increased to be comparable to that of the present RPR (rapid plasma reagin) test antigen, by eliminating portions of the natural components that cross-react with diseases other than syphilis. Use of synthetic components also makes the reagent more stable than the prior version, which results in extended shelf life at the same temperature (usually room temperature) due to elimination of impurities and possible oxidation sites.