Sensitivity and specificity of various serologic tests for detection of Toxoplasma gondii infection in naturally infected sows

The sensitivity and specificity of various serologic tests for antibodies to Toxoplasma gondii were compared in 1,000 naturally exposed sows, using isolation of viable T gondii as the definitive test. Serum samples obtained from heart blood of 1,000 sows from Iowa were examined for T gondii antibodies by use of the modified agglutination test (MAT), latex agglutination test (LAT), indirect hemagglutination test (IHAT), and ELISA. Toxoplasma gondii was isolated from 170 hearts of 1,000 sows by bioassays in mice and cats. The percentage of samples diagnosed as positive for each of the serologic tests was: MAT = 22.2% (titer greater than or equal to 1:20), IHAT = 6.4% (titer greater than or equal to 1:64), LAT = 10.4% (titer greater than or equal to 1: 64), and ELISA = 24.1% (OD > 0.360). The sensitivity and specificity of these tests were calculated respectively to be: 82.9 and 90.29% for MAT, 29.4 and 98.3% for IHAT, 45.9 and 96.9% for LAT, and 72.9 and 85.9% for ELISA. The dye test was run at 1:20 dilution on only 893 sera because of bacterial contamination and presence of anticomplement substances. Dye test antibodies were found in 17.8% of the sera, and sensitivity and specificity were 54.4 and 90.8%, respectively. Thus, the MAT had the highest sensitivity among all serologic tests used.