Multiplex Immunoassay Diagnoses Toxoplasmosis and Rubella

Primary infections of Toxoplasma and rubella in pregnant women may result in vertical transmission of the pathogens, which can cause congenital disease that significantly affects fetal development.

Since clinical manifestations of toxoplasmosis and rubella can be absent or nonspecific, serological screening for both diseases in pregnant women is routinely performed worldwide. Currently, tests such as enzyme immunoassay (EIA), enzyme-linked fluorescent assay (ELFA), chemiluminescent microparticle immunoassay, and electrochemiluminescence immunoassay are widely applied in clinical laboratories to diagnose toxoplasmosis.

Scientists at the Carlos Chagas Institute (Curitiba, Brazil) developed a multiplex assay for simultaneous detection of immunoglobulin G (IgG) antibodies produced during toxoplasmosis and rubella infection. They used a quality control panel of contains 92 anti-Toxoplasma gondii IgG-positive serum samples and 30 negative serum samples. The samples were tested for T. gondii IgG by a Vidas ELFA assay. There is no clinical data associated with these samples. To develop assays for the detection of rubella, 23 serum or plasma samples classified as positive for anti- Rubella virus IgG antibodies and two samples negative for anti-R. virus IgG antibodies were used.

The multiplex assay, based on xMap technology to simultaneously diagnose toxoplasmosis and rubella was designed with the best-performing antigens in singleplex and multiplex assays, which included CTOXH, T. gondii lysate, TOX8131, E-1, and E-2. The multiplex assay showed 100% sensitivity and specificity for anti-T. gondii IgG detection and 95.6% sensitivity and 100% specificity for anti-R. virus IgG detection. Fluorescence and median fluorescence intensity (MFI) were determined using a Luminex 200 reader.

The authors concluded that despite the difficulties related to developing multiplex systems, different types of antigens (extracts and recombinant proteins) can be used to develop high-performance diagnostic tests. The assay developed is suitable to screen for prior T. gondii and R. virus infections, because it is a rapid, high-throughput, low-cost alternative to the current standard diagnostic tools, which require multiple individual tests. The study was published in the June 2017 issue of the journal Memórias do Instituto Oswaldo Cruz.

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Carlos Chagas Institute