Evaluation of a recombinant MIC3 based latex agglutination test for the rapid serodiagnosis of Toxoplasma gondii infection in swines

The entire gene encoding microneme protein 3 (MIC3) from Toxoplasma gondii was cloned into the plasmid pGEX-KG and subsequently expressed in Escherichia coli as a glutathione-S-transferase (GST) fusion protein. The recombinant MIC3 (rMIC3) was purified and evaluated in a latex agglutination test (LAT) as the diagnostic antigen for the detection of antibodies to T. gondii in pig sera. The specificity, stability, and reproducibility of the test were examined. No agglutination was found when the sensitized latex beads were mixed with phosphate-buffered saline (PBS), borate-buffered saline (BBS), normal saline, and negative serum samples. There was no cross-reactivity with the standard positive sera of other pathogens. But intense agglutination occurred with T. gondii antibody positive serum samples. In our study, the coincidence rate of tested positive-sera of the LAT with rMIC3-sensitized latex particles and the ELISA with rSAG1 was up to 92.8%, T. gondii specific antibodies were detected by the LAT in all piglets that were experimentally infected with T. gondii tachyzoites from 8 to 42 days after infection. Our results indicated that the rMIC3 based latex agglutination test appears to be suitable for the detection of T. gondii antibodies at the early stage of infection.