Attenuation of bovine herpesvirus type 1 by deletion of its glycoprotein G and tk genes and protection against virulent viral challenge

To develop a novel vaccine against infectious bovine rhinotracheitis (IBR), a bovine herpesvirus-1 (BoHV-1) mutant was constructed by deleting the genes for glycoprotein G (gG) and thymidine kinase (tk) through homologous recombination. The resulting sequences for both genes were shown to be correct and a gG expression defect was also confirmed. A parallel study of the BoHV-1 gG−/tk−, gE−/tk− mutants and wild type (wt) in 31 calves was performed at three different doses, 4 × 105 PFU, 4 × 106 PFU and 4 × 107 PFU. Compared to wt BoHV-1, inoculation of BoHV-1 gG−/tk− and gE−/tk− produced no clinical signs and the virus was not reactivated by dexamethasone (dex). Inoculation of BoHV-1 gG−/tk− at the doses of 4 × 106 and 4 × 107 PFU provided full clinical protection for the cattle against wt BoHV-1 challenge at 4 × 107 PFU/calf. Although the mutants were associated with significantly lower levels of serum neutralizing antibody, interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) than wt BoHV-1 on days 3, 5 and 7 after immunization, stimulation of IFN-β by BoHV-1 gG−/tk− was significantly higher than that of wt BoHV-1 and gE−/tk− on days 3 and 5. We conclude that BoHV-1 gG−/tk− was attenuated adequately and that it maintains the ability to stimulate immune protection. Therefore, it may be a promising candidate for a marker vaccine against IBR.

► BoHV-1 gG−/tk− mutant could stimulate cell mediated immunity and humoral immunity response.
► The mutant could not be reactivated by dex injection.
► It could provides a good level of protection.