Evaluation of an antigen-capture ELISA for the detection of bovine herpesvirus type 1 shedding from feedlot cattle

Evaluation of a blocking enzyme-linked immunosorbent assay for serological diagnosis of Bovine herpesvirus 1

Bovine herpesvirus 1 (BoHV-1) is an infectious agent of concern in the international export of bovine products; it is endemic in the United States, but it has been eradicated in many countries of the European Union (EU). For export of semen to the EU, accurate assessment of BoHV-1 status of the bull is required and is usually accomplished by measuring the level of antibody to the virus. The gold standard is virus neutralization (VN) using overnight incubation with the virus, a test approved by the World Organization for Animal Health (OIE). Enzyme-linked immunosorbent assay (ELISA) is also approved for international trade. The lone U.S. Department of Agriculture-approved commercial ELISA was compromised with specificity problems, which necessitated the development of a different ELISA. Of 4 monoclonal antibodies evaluated, 1 directed against glycoprotein C of BoHV-1 was found to be the most reliable. One hundred twenty-eight characterized positive samples and 334 negative serum samples were tested. The blocking ELISA showed 97.7% sensitivity and 99.4% specificity as compared with OIE VN. The Wisconsin Veterinary Diagnostic Laboratory ELISA fulfills the OIE requirement for a blocking or competitive ELISA to qualify animals for export to BoHV-1-free countries.

Evaluation of baculovirus-expressed bovine herpesvirus-1 (BHV-1) glycoproteins for detection and analysis of BHV-1-specific antibody responses

Baculovirus (Autographa californica nuclear polyhedrosis)-expressed bovine herpesvirus-1 (BHV-1) glycoproteins B (gB), gC, and gD were developed and characterized. The recombinant proteins retained their antigenic properties as determined by immunoblotting against monoclonal antibodies. The proteins were examined as antigens for detection of BHV-1 infection and for the analysis of antibody responses to the individual viral proteins. A total of 115 bovine serum samples were tested for their reactivity with individual recombinant proteins from baculovirus-infected Spodoptera frugiperda (SF-9) cell lysates by enzyme-linked immunosorbent assay (ELISA), western blotting, and dot blotting assays. These serum samples were previously tested for BHV-1-specific antibodies by virus neutralization (VN) at the veterinary diagnostic laboratory. All 90 serum samples tested positive with VN were positive by ELISA against gC and gD, separately. However, reactivities of sera against gB were generally low and inconsistent. On the other hand, out of 25 sera that were negative with VN, 22 sera were consistent and gave negative results against gC or gD by ELISA, whereas reactivities with gB were inconsistent. Similar results were obtained when the sera were tested by western blotting and dot blotting. The positive sera consistently reacted strongly against gC and to a lesser extent gD. These results suggest that baculovirus expressed gC from infected cell lysate can be used as a potential diagnostic antigen for detection of anti-gC-specific antibody responses in BHV-1 infected cattle.

Epitope-specific antibody responses in market-stressed calves to bovine herpesvirus type 1

Reciprocal competition ELISA (rcELISA) was conducted to map monoclonal antibodies (mAbs) reactive with gI, gIII and gIV glycoproteins of bovine herpesvirus type 1 (BHV-1) into epitope groups. mAbs to glycoproteins gI and gIV were divided into six epitope groups each, while gIII mAbs had been previously divided into four areas. mAbs were chosen from each epitope group to compete in cELISA wih bovine sera collected during a typical regimen of vaccination and transportation from farm to auction to feedlot. The immunodominant epitopes were identified for each BHV-1 glycoprotein. With glycoprotein gI, three epitopes defined by mAbs 1F10, D9 and 4807 were the most dominant; with glycoprotein gIII epitopes defined by mAbs G2 and 1507, and with glycoprotein gIV epitopes defined by mAbs 1102, 1106, 3C1, 3402 and 3E7 showed the maximum responses. The overall cELISA responses to each glycoprotein among two vaccination groups were also compared and it was shown that cELISA responses were significantly higher for each glycoprotein in calves receiving two vaccinations, one on the farm of origin and one at auction, than in calves receiving only one vaccination at auction.