Comparison and Evaluation of Recombinant Antigens for ELISA-Based Diagnosis of Schistosoma japonicum Infection in Goats

To address diagnostic challenges associated with caprine schistosomiasis under persistent transmission risks, this study evaluated the diagnostic performance of four recombinant antigens (rSjSAP4, rSj32, rSjCB1, and rSj23), with soluble egg antigen (SEA) serving as the reference comparator. An optimized indirect enzyme-linked immunosorbent assay (ELISA) was used to test serum samples from well-characterized goat panels, comprising 94 positive samples from goats experimentally infected with Schistosoma japonicum and 100 negative samples. Of the four recombinant antigens evaluated, rSjCB1 demonstrated the highest sensitivity (97.87%), whereas rSjSAP4 exhibited the highest specificity (98.00%). Receiver operating characteristic (ROC) curve analysis yielded Area Under the Curve (AUC) values of 0.8497, 0.9895, 0.8928, and 0.8050 for rSjSAP4, rSjCB1, rSj32, and rSj23, respectively. A mixture containing equal concentrations of rSjCB1 and rSjSAP4 achieved balanced performance (sensitivity: 93.62%, specificity: 92.00%; AUC = 0.9472) and excellent agreement with the reference standard (κ = 0.86). In conclusion, rSjCB1 appears to be the most promising single diagnostic antigen, and an equal-concentration mixture of rSjCB1 and rSjSAP4 represents a practical diagnostic alternative to SEA for the development of rapid and accurate immunoassays for caprine schistosomiasis.