Enzyme-Linked Immunosorbent Assay Based on a Chimeric Antigen Bearing Antigenic Regions of Structural Proteins E 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 and the N-terminal antigenic region (residues 1 to 136) of protein E2 were constructed in the form of a fused, chimeric protein, C21EE2, 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 fragment (Eaa 109–160) or an E2 fragment (E2aa 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 C21EE2 would improve serodiagnostic sensitivity and allow for the detection of CSFV infection as early as 7 dpi.