Application of competitive enzyme-linked immunosorbent assay for the serologic diagnosis of classical swine fever virus infection

A competitive enzyme-linked immunosorbent assay (C-ELISA), based on a trunc ated E2 recombinant protein of the Alfort/187 strain of classical swine fev er virus (CSFV) and a specific monoclonal antibody M1669, was evaluated usi ng 2,000 sera from clinically healthy pigs in Canada (a CSFV-free country) and sera from experimentally infected pigs. The relative specificity and se nsitivity of the C-ELISA were 100% and 86%, respectively, at a cutoff of 25 % inhibition using negative and positive pig sera, as defined by the neutra lizing peroxidase-linked assay (NPLA). A kappa value of 0.91 was obtained, indicating an excellent level of agreement between the NPLA and the C-ELISA . When sera from 120 infected pigs were used in the test at greater than or equal to 21 days postinfection, the sensitivity of the C-ELISA and the kap pa value increased to 97% and 0.98, respectively. This C-ELISA will be usef ul when a large number of samples must be tested, as could occur during a d isease outbreak or for surveillance or prevalence studies.