Determination of the lowest valuable titer [Cut-off titer] of antitoxoplasma antibodies for detection of Toxoplasmosis in sheep by ELIS A and IFA tests

ABSTRACT

To investigate 1] the cut-off liters of antitoxoplasma antibodies through in IgG- ELIS A and IFA tests and 2] application of IgG- ELIS A rather than IFA test for diagnosis of toxoplasmosis [Toxoplasma gondii] in mature sheep. One hundred and ten Iranian mature sheep. The serum samples were examined to determine the final positive dilution of antitoxoplasma antibody by IgG-ELIS A and IFA tests. For this purpose, immunoreactivity of the final positive dilution of each serum with to SAG-1 antigen was determined by western blot analysis. The ELIS A microplate coated with 105 tachyzoites/ well, was incubated with diluted sheep sera. After adding of substrate, enzymatic activity was measured at 492 nm. Samples with higher absorbance values [=2.5 times greater than these values of negative controls] designated as positive.The data obtained from 110 sera with IFA and ELIS A was compared with each other to determine the percentage of agreement between them. Using a chi-square test to show the significant differences between results of IFA and ELIS A. Furthermore, these results were compared to determine the percentage of agreement between them. 24 out of 110 serum samples were concordant positive [21.8%] and 79 cases [70.9%] were concordant negative in both IFA and ELISA. All positive samples exhibited strong reactivity to SAG-1 [30 KD band]. Among 110 serum samples, five discordant ELISA- positive and two discordant IFA- positive sera had no reactivity with SAG-1 band in WB. Moreover, there is 92.7% coincidence between results of ELISA and IFA tests. In this study the lowest valuable titer, for detection of Toxoplasmosis in sheep, was obtained as 140 and 1100 in the IFA and ELISA tests, respectively. Furthermore, immunoreactivity of serum dilutions to S AG-1 antigen in the WB proved to be a useful tool for setting of optimum cut-off liters in the IFA and ELISA tests