An ELISA Using a T. gondii GRA6-Derived Peptide as Antigen Successfully Detected Ovine Toxoplasmosis

Toxoplasma gondii is considered the second most common pathogen causing abortions in sheep, resulting in great economic losses. Thus, timely, sensitive and specific diagnosis of ovine toxoplasmosis is very important. In this study, diagnostic performance of an ELISA using a T. gondii GRA6 peptide (GRA6 ELISA) was investigated using serum samples (n = 61) collected from sheep diagnosed with toxoplasmosis using a commercial ELISA kit. Additionally, an in house ELISA using T. gondii tachyzoite lysate antigen (TLA ELISA) was also used to compare its performance with that of the GRA6 ELISA. Using the commercial ELISA kit as reference, the TLA ELISA and the GRA6 ELISA showed sensitivities of 83.7% and 88.4%, and specificities of 85% and 80.0%, respectively. Cohen's kappa coefficient between TLA ELISA/ GRA6 ELISA and commercial ELISA kit was 0.652 and 0.675, respectively, indicating that both tests have good agreements. When we analyzed serum samples (n = 19) collected from a sheep group that had experienced abortions and were diagnosed with toxoplasmosis using a commercial ELISA kit, sensitivity values for the TLA ELISA and the GRA6 ELISA reached 100% and 89.5%, respectively. According to the seroprevalence results in serum samples analyzed, the commercial ELISA kit detected seroprevalence as 68.2% whereas the GRA6 ELISA and TLA ELISA detected seroprevalence as 66.7% and 61.2%, respectively. Furthermore, among the serum samples that yielded compatible results across the three different ELISA assays (n = 45), 31 were identified as seropositive, corresponding to a seroprevalence rate of 68.9% (31/45). In conclusion, the GRA6 ELISA detected ovine toxoplasmosis with high sensitivity and specificity.