A glycoprotein E deletion mutant of bovine herpesvirus 1 is avirulent in calves

A marker vaccine elicits an antibody response in the host that can be distinguished from the antibody response induced by a wild-type strain. To obtain a bovine herpesvirus 1 (BHV-1) marker vaccine, we constructed a glycoprotein E (gE) deletion mutant. This was obtained by removing the complete gE coding region from the BHV-1 genome. To attenuate the gE deletion mutant further, we also introduced a small deletion in the thymidine kinase (TK) gene. We selected three mutants: the gE deletion mutant, a TK deletion mutant and a gE/TK double deletion mutant, and examined their virulence and immunogenicity in calves. After intranasal inoculation, the TK deletion mutant showed some residual virulence, whereas the gE and gE/TK deletion mutants were avirulent. The calves inoculated with the deletion mutants were protected against disease after challenge exposure and shed significantly less virus than control calves. Deleting the gE gene, therefore, has little effect on the immunogenicity of BHV-1, but is sufficient to reduce the virulence of BHV-1 in calves. These findings led us to conclude that the gE deletion mutant is a good candidate for a modified live BHV-1 marker vaccine.