Development and application of an enzyme-linked immunosorbent assay for detection of bovine viral diarrhea antibody based on Erns glycoprotein expressed in a baculovirus system

The BVDV envelope glycoprotein E-rns/gp48 and the C terminal 79 amino acids of the capsid protein coding region were expressed in a baculovirus system and antigenically characterized. Western blot assay was used to detect recombinant E-rns (r-E-rns) in infected insect cells using specific monoclonal antibodies. The r-E-rns was then used in an indirect ELISA to detect BVDV specific antibodies in a panel of 540 well-characterized sera. Results of the r-E-rns ELISA were compared to those obtained with a commercially available competitive ELISA targeting anti-NS2/3 antibodies. A good correlation was observed between the 2 ELISA (kappa = 0.916, 95% CI.: 0.876, 0.956). Using the commercial NS2/3 ELISA as the reference test, the relative sensitivity of r-E-rns ELISA was 97.5% (95% C.I.: 94.3%, 99.1%) and the relative specificity was 93.9% (95% C.I.: 89.4%, 96.9%), while relative specificity was 100% (95% C.I.: 97%, 100%) using true negative sera (derived from a negative herd). All but 1 antigen positive animals (n = 36) tested negative in the r-E-rns ELISA; among them all 22 confirmed PI animals were negative by r-E-rns ELISA. The ability of r-E-rns ELISA to identify cattle immunized with inactivated vaccine was also demonstrated in a small group of cattle, compared to an NS2/3 antibody ELISA. Results suggest that r-E-rns ELISA represents an alternative test for antibody generated by natural infection or BVDV vaccination.