Literature review > Issue_1 > Review Hagedorn et al. 

Standard syphilis serologic diagnosis still relies on the application of a screening non-treponemal test (i.e. VDRL, RPR) and further confirmation with a specific treponemal test (i.e. FTA-ABS, TPHA). The reference paper provides sound data about the performance of a new treponemal serologic test. INNO-LIA™ Syphilis is a line immunoassay (LIA), for in vitro use, to confirm the presence of antibodies against Treponema pallidum in human serum or plasma (www.innogenetics.com/site/diagnostics.html). It was evaluated against a gold standard based on a consensus diagnosis of syphilis derived from conventional serology, for a few hundred serum samples previously known to be positve, negative, or indeterminate for anti-treponemal antibodies. Sensitivity and specificity values of this multiparameter imunnoassay obtained by the authors of this report were very high, 100% and 99.3%, respectively.

The INNO-LIA™ Syphilis test belongs to a generation of recently developed treponemal antibody tests, founded on the principles of DNA recombinant technology that has allowed the availability of T. pallidum antigens like TpN15, 17, 47 and TmpA. Actually, this test employs all four proteins, a characteristic which has been shown to render better results than tests using a single treponemal antigen for antibody detection. [1].

Syphilis continues to be a worldwide public health problem, and yet is a sexually transmitted disease successfuly treated when timely diagnosed. Thus, the advent of confirmatory diagnostic alternatives that seem to perform more efficiently than traditional tests adds to the feasibility to improve treatment and control the infection. In fact, because of their results, the authors consider "the INNO-LIA Syphilis to be a valid, if not superior, alternative to the FTA-ABS test for the confirmation of syphilis screening test findings".
In this regard, I would like to pose some observations that can be further addressed:
a) There remains to be shown the performance of the test in prospective studies and perhaps compare it to another investigational status test, for example to the T. pallidum particle agglutination test; as this treponemal confirmatory assay has been shown to be reliable, relatively rapid and easy to perform. [2].
b) It may be desirable to assess the usefulness of the test by obtaining information on its predictive values for the different stages of syphilis.
c) The overnight incubation procedure for test strips and probably an expected high cost (not mentioned by the authors, approximately 30 USD per test based on a price quotation from Innogenetics), may prove to be limiting factors for the generalized use of this line immunoassay syphilis kit.
d) Taking into consideration the manufacturer´s statement that: "no cross-reactivities were reported with pathologic samples originating from autoimmune diseases, Lyme borreliosis, biological false-positives, or with samples from pregnant women" (www.innogenetics.com/site/diagnostics.html), it must be said that at present there is no laboratory test able to discriminate between antibodies to Treponema pallidum and the pathogenic treponemes: T. pertenue and T. carateum, the agents of yaws and pinta disease, respectively. The endemic treponematoses have not yet been eliminated and are currently thought to affect at least 2.5 million persons in tropical regions from developing countries [3-5]. Therefore, it might be interesting to challenge the INNO-LIA Syphilis with yaws and pinta positive sera.

References:

1. Morse, S.A. 2003. Advances in diagnostic tests for bacterial STDs. Salud Publica Mex. 45 Suppl. 5: S698-S708.

2. Pope, V., M. B. Fears, W.E. Morrill, A. Castro, and S.E. Kikkert. 2000. Comparisson of the Serodia Treponema pallidum particle agglutination, Captia Syphilis-G, and SpiroTek regain II tests with standard test techniques for diagnosis of syphilis. J. Clin. Microbiol. 38: 2543-2545.

3. Radolf, J.D., E.B. Lernhardt, T.E. Fehniger, and M.A. Lovett. 1986. Serodiagnosis of syphilis by enzyme-linked immunosorbent assay with purified recombinant Treponema pallidum antigen 4D. J. Infect. Dis.153: 1023-1027.

4. Fohn M.J., S. Wignall, S.A. Baker-Zander, and S.A. Lukehart. 1988. Specificity of antibodies from patients with pinta for antigens of Treponema pallidum subspecies pallidum. J. Infect. Dis.157: 32-37.

5. Antal, G.M., S.A. Lukehart, and A.Z. Meheus. 2002. The endemic treponematoses. Microbes. Infect. 4: 83-94.

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