Performance of commercial ELISA and agglutination test kits for the detection of anti-Toxoplasma gondii antibodies in serum and muscle fluid of swine infected with 100, 300, 500 or 1000 oocysts.

Serum and tissue fluid samples from experimentally infected swine were tested for antibodies to Toxoplasma gondii using both an indirect ELISA and a modified agglutination test (MAT) available commercially in kit form. Ten 8-9 week-old swine were fed meatballs containing 100, 300, 500 or 1000 T. gondii oocysts and three control animals were fed meatballs with no oocysts. Post-inoculation blood samples were collected weekly until euthanasia at 35-63 days post inoculation (DPI). Tissue fluid was obtained from diaphragm, heart and sternomastoideus muscles post-mortem. By 16 DPI, nine of 10 inoculated pigs were detected serologically using ELISA at a pre-test serum dilution of 1:50 and all ten pigs were detected by the MAT at a serum dilution of 1:25. The last pig became positive on ELISA by 21 DPI and the 10 pigs maintained their serological status for the duration of the experiment. Heart muscle was the best overall source of tissue fluid for ELISA and all six pigs inoculated with either 500 or 1000 oocysts were positive using either diaphragm or heart tissue fluid samples. However, 10 of 18 fluid samples from pigs receiving ≤ 300 oocysts were not detected using ELISA, including 5 of 6 from sternomastoideus muscle. The MAT used at a 1:10 pre-test dilution of tissue fluid correctly identified all 10 inoculated pigs regardless of the source muscle. Based on these data, we conclude that either assay would be useful for herd evaluation or surveillance testing using sera, and the MAT would be a good candidate assay for testing tissue fluid for the same purposes.