Correlation of the classical swine fever (CSF) antibody levels detected by serum neutralizaton and enzyme-linked immunosorbent assay (Elisa)

Classical swine fever is an important viral disease that has a devastating impact on the swine industry. The Enzyme-linked immunosorbent assay (ELISA) provides a simpler and more practical approach to detect classical swine fever virus (CSFV) antibodies compared to the serum neutralization (SN) test. However, antibody responses detected by ELISA cannot directly exhibit a protective level. This study aimed to evaluate the correlation of classical swine fever antibody responses detected by SN assay and commercial ELISA. A total of 522 negative and positive serum samples were tested by the SN and ELISA. Correlation, an agreement between two assays, and comparisons of sample-to-positive (S/P) values among the level of SN titers were evaluated. The results revealed a strong positive relationship (rs 0.89; p<0.0001) and excellent agreement with the Kappa value of 0.913 between the S/P values and SN titers. The comparison tests showed a statistically significant difference (p<0.0001) between the mean S/P values among three distinct levels of SN titers, i.e., negative SN titers (antibody titer <2), SN titers below protective level (antibody titer <32), and SN titers at protective levels (antibody titer ≥32). Positive samples having antibody titers below and at protective levels showed S/P values at 1.132±0.587 and 1.767±0.479, respectively. Therefore, the strong correlation between the S/P values and neutralizing antibody titers could provide useful information in terms of detecting CSFV antibodies and estimating protective status of antibody positive animals by the ELISA method.