Statistical analysis.

Pearson’s coefficient test was used to determine the correlation between the NA-ELISA titers and the VNT titers, and a P value of <0.05 was considered statistically significant.

Receiver operating characteristic (ROC) curve analysis (21) was used to estimate the cutoff value, sensitivity, and specificity of the assay by using 126 serum samples from naive bovines (serum sample set I) and 97 serum samples from experimentally infected animals (serum sample set II).

Statistical analysis, including Pearson’s coefficient test and ROC curve analysis, was performed using GraphPad Prism (version 6.0) software (San Diego, CA, USA).