One point dilution enzyme-linked immunosorbent assay (ELISA) for Toxoplasma gondii seroepidemiological surveys

A one point dilution enzyme-linked immunosorbent assay (ELISA) procedure suitable for determining immunoglobulin G (IgG) antibody levels to Toxoplasma gondii (T. gondii) in community seroepidemiological surveys is described. A two-fold serial dilution ELISA procedure was first used to determine the IgG titers in 56 and 83 sera earlier screened by the Sabin-Feldman dye test (DT) and the indirect hemagglutination test (IHA), respectively. The regression rate of the results by the DT and ELISA was 0.92. Comparison of the results by the IHA and the two-fold serial dilution ELISA gave regression coefficient of 0.92. Using the absorbance values for the test sera at dilutions of 1:20, standard curves made by plotting the optical density versus the corresponding dilution factor of a control sera were used to estimate the antibody levels. The regression coefficient of the results by the two-fold serial dilution method and those by the curves for sera with titers of up to 1:320 was 0.97. The curves could not, however, estimate accurately the antibody level in sera with titers above 1:320. The one point dilution ELISA described is a useful epidemiological tool for the screening of IgG antibody to Toxoplasma gondii in the community. However, larger series are required to confirm our observations.