Development of a competitive ELISA using a truncated E2 recombinant protein as antigen for detection of antibodies to classical swine fever virus

The sequence encoding a truncated E2 glycoprotein of the Alfort/187 strain of classical swine fever virus (CSFV) was expressed in Escherichia coli using the PET expression system and the recombinant product purified by Ni-NTA agarose affinity chromatography. The antigenicity of this recombinant protein was demonstrated by immunoblot using anti-CSFV-specific antibodies. A monoclonal antibody was produced against the truncated E2 protein and used as competitor in an ELISA for the detection of antibodies to CSFV. Specific antibodies were demonstrated by competitive ELISA (C-ELISA) as early as 21 days post-infection (dpi) in experimentally infected pigs. Seroconversion was demonstrated by C-ELISA and neutralising peroxidase-linked assay (NPLA) in all infected animals by 4 weeks. No cross-reaction with antibodies to bovine viral diarrhoea virus (BVDV) was seen in the C-ELISA using sera from experimentally infected pigs. The C-ELISA is not intended as a substitute for the NPLA. However, it is expected it will be useful for monitoring and prevalence studies. It will also assist in testing a large number of samples in the event of an outbreak. (C) 2001 Harcourt Publishers Ltd.