Cloning of the bovine immunodeficiency virus gag gene and development of a recombinant-protein-based enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was established for the rapid detection of specific bovine immunodeficiency virus (BIV) antibodies in cattle, using recombinant Gag protein as an antigen. The gag coding region from BIV was cloned into an expression vector, pQE32, which expressed high levels of recombinant protein from Escherichia coli. The ELISA was standardized by a checkerboard titration against known BIV-positive and - negative sera from cattle and a monoclonal antibody to the Gag protein. A total of 139 cattle serum samples, from the diagnostic laboratory at Kansas State University, Manhattan, and from the Dairy Station, Louisiana State University, Baton Rouge, were compared by ELISA and immunoblot assays for the detection of BIV-specific antibodies. Of 26 cattle sera samples which tested positive using the immunoblot assay, 23 were positive by ELISA, thus establishing a strong correlation between the two tests. The sensitivity and specificity of ELISA relative to immunoblotting were 0.88 and 0.93, respectively. ELISA proved to be as specific as immunoblotting but was much less time-consuming and easier to perform.