Enzyme-linked immunosorbent assay based on a chimeric antigen bearing antigenic regions of structural proteins Erns and E2 for serodiagnosis of classical swine fever virus infection.

The antigenic region (residues 109 to 160) of classical swine fever virus (CSFV) protein E(rns) and the N-terminal antigenic region (residues 1 to 136) of protein E2 were constructed in the form of a fused, chimeric protein, C21E(rns)E2, for use as an enzyme-linked immunosorbent assay (ELISA) antigen for the serodiagnosis of CSFV infection. Tested with 238 negative-field (CSFV-free) sera from Canadian sources, the specificity of the ELISA was determined to be 93.7%. All 20 sera from experimentally infected pigs representing a variety of animals, virus strains, and days postinfection (dpi; range, 7 to 210) were detected as positive (100%). In contrast, an ELISA based on an E(rns) fragment (E(rns)(aa 109-160)) or an E2 fragment (E2(aa 1-221)) identified only 18 (90%) of 20 sera from infected pigs as positive, missing two targets collected at 7 dpi. These data suggest that use of the chimeric antigen C21E(rns)E2 would improve serodiagnostic sensitivity and allow for the detection of CSFV infection as early as 7 dpi.