Viral status and antibody response in cattle inoculated with recombinant bovine leukemia virus-vaccinia virus vaccines after challenge exposure with bovine leukemia virus-infected lymphocytes

Abstract

Objective. To determine the bovine leukemia virus (BLV) antibody response and infectivity status in BLV-vaccinated cattle after challenge exposure with BLV-infected lymphocytes. Design. Steers were inoculated with vaccinia virus constructs expressing the gag, pol, and env genes of the BLV or the env gene only of the BLV genome, then challenge exposed with BLV-infected lymphocytes. The steers' BLV antibody and infectivity status was monitored. Animals. Fifteen 8- to 9-month-old Holstein steers previously determined to be BLV antibody and BLV negative. Procedure. 1 month after second inoculation, steers were challenge exposed with 106 BLV-infected lymphocytes from a highly infective BLV-positive cow. Serum and blood lymphocytes were obtained regularly for 6 months. The agar gel immunodiffusion assay, ELISA, and serum neutralization assay were used to detect BLV antibody in serum of steers. The sheep infectivity and syncytium-forming assays were used to determine the viral status of the steers. Results. Differences were seen in antibody responses between the BLV-vaccinated and non-BLV-vaccinated control groups. All cattle were susceptible to infection when challenge exposed with BLV-infected lymphocytes. Conclusion. Despite the enhanced immune response in the BLV-vaccinated cattle after challenge exposure, none of the BLV-vaccinated cattle was protected from BLV infection. Clinical Relevance. Vaccination is not an affective way to protect cattle from BLV infection.