Detection of antibodies against the core protein p24 of the bovine leukaemia virus in cattle for confirmatory serological testing.

An electrophoretic immunoblotting technique which was developed recently was evaluated for the identification of serum antibodies against the bovine leukaemia virus core protein p24 by using 167 sera from a bovine leukaemia virus-negative herd, and 144 sera from herds naturally infected with the virus. The sensitivity of the immunoblot was 97.4%, relative to sera which were positive in the polymerase chain reaction and in a commercial EBL-ELISA. The specificity of the immunoblot was 99.4%, for the sera from a cattle herd in which all animals were negative by a commercial EBL-ELISA, and it was 96.7% relative to sera which were negative by the polymerase chain reaction and by the agar gel immunodiffusion test from bovine leukaemia virus-infected cattle herds. A p24-specific ELISA was developed, using a monoclonal anti-p24 antibody for coating microtitre plates, a crude antigen preparation, and a monoclonal anti-bovine IgG-horse radish peroxidase conjugate as components. All reagents were commercially available. While the p24-ELISA worked well with sera from serial bleeds from calves infected experimentally with the bovine leukaemia virus and its sensitivity with sera from the naturally-infected cattle was 96.5%, its specificity was relatively low at 85.0 or 53.3%, respectively for the two negative sera groups.