An indirect ELISA based on recombinant nucleoprotein for detection of the antibodies to porcine reproductive and respiratory syndrome virus

An indirect ELISA for detection of the antibodies to porcine reproductive and respiratory syndrome virus(PRRSV) was developed using the purified nucleoprotein,and its optimal reaction conditions were determined: coating antigen at 37 ℃ 1 h or 4 ℃ overnight at a concentration of 13.3 μg/mL,5% defatted milk powder as blocking agent at 37 ℃ 2 h,serum sample(1∶40) at 37 ℃ for 90 min,HRP labeled rabbit anti-pig IgG(1∶4000) at 37 ℃ for 40 min,the substrate TMB for ELISA being incubated at room temperature for 15 min.The shreshold of positive and negative sera was 0.434 by statistical analysis.The ELISA assay was confirmed to have a good repeatability,sensitivity and specificity by repeatability test,cross test and blocking test.And compared with the IDEXX Test kit,the sensitivity and specificity of the ELISA were 95.6% and 93.0%,respectively,which showed no significant difference between the two assays.The coincidence rate of the two assays was up to 94.7%.