The development of novel antigens for improved syphilis diagnosis

Syphilis is a disease caused by the bacterium Treponema pallidum subsp. pallidum, which is generally transmitted through sexual contact, or vertically from a mother to her fetus. Syphilis is effectively treated with penicillin yet remains prevalent worldwide, due in part to the shortfalls of current diagnostic tests. Traditional serological testing algorithms screen with diagnostic tests specific for non-treponemal antibodies followed by subsequent screening of reactive samples for treponeme-specific antibodies. Limitations exist with both the sensitivity and specificity of non-treponemal and treponemal tests. Specific enzyme immunoassays, chemiluminescence assays and rapid point-of-care tests have been developed that contain the T. pallidum proteins TpN15 (Tp0171), TpN17 (Tp0435), TpN47 (Tp0574), and/or TpN44 (Tp0768; TmpA). These tests have also been shown to have suboptimal sensitivities, highlighting the need for identification of novel syphilis diagnostic candidates. In this study, soluble recombinant versions of two previously identified diagnostic candidates, Tp0326 and Tp0453, as well as a novel Tp0453-Tp0326 chimera were produced. The sensitivity of these recombinant proteins in enzyme-linked immunosorbant assays (ELISA) for diagnosis of syphilis was determined by screening characterized serum samples from primary, secondary, and latent stages of infection (n=169). The specificity was determined by screening uninfected individuals (n=13), false positives identified via the standard testing algorithm (n=19), and potentially cross-reactive infections caused by Leptospira, B. burgdorferi, H. pylori, Epstein-Barr virus, hepatitis B virus, hepatitis C virus, and cytomegalovirus (n=38). The sensitivities for Tp0326, Tp0453, and the Tp0453-Tp0326 chimera were found to be 86%, 98% and 98%, respectively. The specificities for Tp0326, Tp0453, and the Tp0453-Tp0326 chimera were found to be 99%, 100% and 99%, respectively. These findings suggest that Tp0453 and the Tp0453-Tp0326 chimera show promise as novel syphilis-specific diagnostic candidates for accurate detection of all stages of infection and for future development into numerous diagnostic test formats including enzyme immunoassays, chemiluminescence assays, and rapid point-of-care tests.