New Proteins for a New Perspective on Syphilis Diagnosis

Abstract

Syphilis is a sexually transmitted disease caused by Treponema pallidum subsp. pallidum; it can be effectively treated with penicillin yet remains prevalent worldwide, due in part to the shortcomings of current diagnostic tests. Here we report the production of soluble recombinant versions of three novel diagnostic candidate proteins, Tp0326, Tp0453, and a Tp0453-Tp0326 chimera. The sensitivities of these recombinant proteins were assessed by screening characterized serum samples from primary, secondary, and latent stages of infection (n ‫؍‬ 169). The specificities were assessed by screening false positives identified with the standard diagnostic testing algorithm (n ‫؍‬ 21), samples from patients with potentially cross-reactive infections (Leptospira spp., Borrelia burgdorferi, Helicobacter pylori, Epstein-Barr virus, hepatitis B virus, hepatitis C virus, or cytomegalovirus) (n ‫؍‬ 38), and samples from uninfected individuals (n ‫؍‬ 11). The sensitivities of Tp0326, Tp0453, and the Tp0453-Tp0326 chimera were found to be 86%, 98%, and 98%, respectively, and the specificities were 99%, 100%, and 99%. In a direct comparison, the Captia syphilis (T. pallidum)-G enzyme immunoassay (Trinity Biotech) was used to screen the same serum samples and was found to have a sensitivity of 98% and a specificity of 90%. In particular, Tp0453 and the chimera exhibited superior accuracy in classifying analytical false-positive samples (100%, compared to 43% for the Captia assay). These findings identify Tp0453 and the Tp0453-Tp0326 chimera as novel syphilis-specific diagnostic candidates that surpass the performance of a currently available diagnostic enzyme immunoassay test for syphilis and that allow accurate detection of all stages of infection.

Recent Trends in the Serologic Diagnosis of Syphilis

“…Some experts recommend using second-or third-generation treponemal tests which contain newer and more-specific antigens, but these tests are not yet commercially available (44). Based on local laboratory performance data, some laboratories have elected to use an RPR cutoff value above which further testing is discontinued; for example, in Quebec, Canada, specimens testing EIA positive with RPR values of Ն1:8 dilutions almost always have the positive result confirmed when tested with a second TT, and a second TT is not routinely done in such situations (Bouchra Serhir, personal communication).…”

A better definition of active syphilis infection

“…Treponemal-specific IgM and IgG antibodies are usually generated two and four weeks after infection, respectively [4], appearing earlier than nontreponemal antibodies. The IgM antibody may persist and does not disappear, even if the patient receives adequate treatment [5,6]. Moreover, reaginic antibodies may be negative in cases of late, latent, or post-treatment syphilis (due to seroreversion) [7].…”

Evaluation of the recombinant protein Tp0965 of Treponema pallidum as candidate antigen for serological diagnosis of syphilis

“…В частности, широкое применение в составе диагно-стических тест-систем получили рекомбинантные белки Tp15, Tp17, Tp47 и TmpA, совместное использование которых обеспечивает 98,3−99,6% специфичность про-водимых диагностических исследований [4]. Однако, достигаемые при этом значения чувствительности су-щественно варьируют на разных стадиях заболевания, оказываясь сниженными в случае первичного и позд-него скрытого сифилиса [5]. Сохраняются сложности диагностики данного заболевания в семейных парах и у беременных, определяемые возможным расхождением результатов различных лабораторных тестов.…”