Comparison of two assays in the diagnosis of toxoplasmosis: immunological and molecular

Serological tests for Toxoplasma gondii are inadequate because antibody production either fails or is significantly delayed. This study in eastern Iraq investigated the IgG-avidity ELISA test for detecting recent T. gondii infections among pregnant women and compared immunological methods and PCR as molecular assays in the diagnosis of T. gondii. Serums samples were taken from 130 pregnant women at risk of toxoplasmosis and a control group of 25 women with normal pregnancy. Of 50 IgM- and/or IgG-positive samples, only 15 showed low IgG-avidity antibodies. PCR was performed on 25 selected samples. Toxoplasma DNA was detected in 15/15 IgM-positive with low IgG-avidity and 1/3 IgM-positive with high IgG-avidity. None of the IgM-negative with high IgG-avidity showed any Toxoplasma DNA. ELISA IgG-avidity when used in combination with ELISA IgG/IgM is a valuable assay for the exclusion of ongoing or recently acquired T. gondii infection in pregnant women.