New Treponemal-Based Immunoassay Kit for Syphilis Provides Advantages over Non-Treponemal Assays

The non-treponemal method for Syphilis detection and screening has been the standard method of choice, however, there has also been a shift to the treponemal method, offering greater precision.

Transasia Bio-Medicals Ltd. (Mumbai, India) has launched a sandwich ELISA based kit, ErbaLisa Syphilis, for detection of total antibodies against Treponema pallidum (TP). TP serology is relatively complex, with different profiles depending on stages of infection and on whether or not treatment has been administered. Detection of total antibodies (IgM, IgG, IgA) helps in screening samples of any type or at any stage of infection. Anti-treponemal IgM antibodies are produced 2 weeks after exposure, followed by IgG antibodies 2 weeks after IgM production.

ErbaLisa Syphilis utilizes recombinant antigens of TP to ensure higher diagnostic sensitivity and specificity compared to non-treponemal tests in cases of primary, tertiary, and congenital syphilis. It also minimizes the cross-reactivity with cardiolipin antibodies. In addition to enabling more advanced screening, advantages of the ELISA format also make ErbaLisa Syphilis attractive for laboratories with large workloads.

"Syphilis continues to challenge clinicians with its nuances in diagnosis and management. Serologic tests are the foundation of syphilis management as Treponema pallidum cannot be cultured in vitro, and knowledge of the diagnostic limitations of these tests is critical for clinicians," said Kejal Mistry, Product Management-Immunology, Transasia Bio-Medicals. Sensitivities of non-treponemal tests vary depending on the type of test and stage of infection, with lower sensitivities in primary and late syphilis. False-positive results are associated with viral infections, pregnancy, malignant neoplasms, autoimmune diseases, and advanced age, while false negatives are observed due to detection of lipodial antibody detection appearing later during infection.

Transasia's ErbaLisa Syphilis test has a specificity of 99% and sensitivity of 99%, with an assay time of 105 minutes (60+30+15 minutes). Reagents are Ready-to-Use, with shelf life of 18 months at 2 °C to 8 °C.

"Commercial ELISA tests have been developed since the World Health Organization (WHO) recommended the use of a combination of a non-treponemal and treponemal test for screening and diagnostic purposes to minimize the risk of syphilis infection through the route of transfusion," added Ms. Mistry. Recommendations: Screening should be performed using a highly sensitive and specific test (TPHA or ELISA) for treponemal antibodies; In populations where there is a high incidence of syphilis, screening should be performed using a non-treponemal assay (VDRL or RPR).

Globally, the VDRL and TPHA combination method is being increasingly replaced with the commercially available ELISAs for treponemal IgG or IgG and IgM. In India, treponemal ELISA has become the first choice for screening populations with early or very late stage of infection in which non-treponemal tests are negative. This helps improve treatment management and in eradicating incidence through transmission or transfusion.

"The CDC (US Centers for Disease Control and Prevention) encourages clinicians to consider treatment for late latent syphilis in individuals with positive treponemal ELISA results to reduce the chance of progression to tertiary complications," said Ms. Mistry. Additional important considerations with the new tests are their Positive Predictive Value (PPV) and Negative Predictive Value (NPV), which depend on disease prevalence. Highly sensitive treponemal ELISAs will be beneficial for diagnosis of patients with suspected syphilis and with no prior history, especially in early or late infections with nonreactive non-treponemal tests.

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