[Evaluation of the usefulness examination of IgG avidity for serodiagnosis of toxoplasmosis].

An assay measuring the avidity of T. gondii-specific IgG is a useful serological indicator of toxoplasmosis which in many cases allows on the basis of single serum sample testing to confirm or exclude acute infection. IgG antibodies against T. gondii produced in the recent primary infection are of low-avidity while IgG antibodies in the chronic toxoplasmosis are of high-avidity. In the present study 80 sera: 47 sera of patients with suspected acute toxoplasmosis, 23 sera of pregnant women and 10 sera of healthy blood donors, were evaluated for the presence of IgM, IgA and IgG antibodies and for the avidity of IgG. Among the 80 tested sera IgM antibodies were present in 34 (42.5%) cases of which 22 (64.7%) showed low-avidity of IgG and the presence of IgA antibodies confirming acute toxoplasmosis. In the rest of these 34 sera three of them showed low avidity index and nine other high avidity in spite of the presence of IgM antibodies. In these 12 sera IgA antibodies were not present. In 46 (57.5%) examined sera IgM or IgA antibodies were not detectable and the present the IgG antibodies showed high-avidity what is characteristic of chronic infection. An assay for evaluation of avidity of IgG antibodies specific for T. gondii is valuable in complementing existing tests and in many cases it has decisive value for interpretation of results.