New methods for the serological diagnosis of syphilis

Abstract

Historically, the serological diagnosis of syphilis requires the detection of two distinct antibodies to different antigen types. Non-treponemal syphilis tests detect antibodies to lipoidal material released from damaged host cells as well as to lipoprotein-like material and cardiolipin released from the treponemes themselves. In contrast, the treponemal tests detect antibodies directed against protein antigens 15, 17 or 47 KD. The treponemal tests are used to verify results obtained with non treponemal tests; also they may be used to confirm a clinical impression of syphilis in patients, as can occur in late syphilis. All these assays are performed using serum samples and must be performed in a laboratory setting. Therefore, test results may not be available for several days after the sample is collected. Because patients attending sexually transmitted disease (STD) clinics often do not return for results, a rapid point of care test that detects antibodies to both non-treponemal and treponemal antigens would be of considerable value in aiding clinicians to make judgment on the necessity for treatment of the disease at the initial clinic visit. New, innovative immunofiltration (flow-through) and immunochromatographic (lateral flow) point of care tests which measure both treponemal and non-treponemal antibodies on the same device have been developed. With these configurations, the assays simultaneously screen for the presence of anti-cardiolipin antibodies and confirm the results by the detection of antibodies to T. pallidum. Currently, the only commercially-available point of care tests are treponemal tests that measure lifetime exposure to syphilis and do not necessarily indicate active infection. Also in these studies, a new and innovative multiplex chemoluminescence assay and an Enzyme Linked Immunosorbent Assay (ELISA) have been developed for simultaneous serologic screening and confirmation of syphilis. These tests can be fully automated could be ideal for high volume testing. The results of such assays will be objective with a numerical cut off value. These tests could ultimately replace the Rapid Plasma Reagin (RPR) for monitoring efficacy of treatment. These innovations represent valuable tools that can be used in both developing and industrialized countries to diagnose syphilis and to initiate and monitor the efficacy of treatment.