Vaccination with bovine herpesvirus 1 inactivated vaccine cannot be considered as a stimulus of reactivation

Abstract

In countries where bovine herpesvirus 1 (BHV-1) infection is highly prevalent, repeated vaccinations of seropositive cattle are recommended to reduce virus circulation with the aim of reaching infectious bovine rhinotracheitis (IBR) free status. In this context, it was of great importance to investigate whether or not vaccination of seropositive latently infected cattle with inactivated vaccine could induce BHV-1 reactivation and re-excretion. Six seronegative calves were intranasally infected with BHV-1 Iowa strain. Four months later, they were randomly allocated in two groups. Four animals were vaccinated twice, four weeks apart, with an adjuvanted inactivated BHV-1 vaccine and two animals were used as controls. After viral inoculation, all calves excreted large amounts of viruses. Following each vaccination, no infectious virus was isolated in the nasal secretions of calves. Three weeks after the second vaccination, all calves were subjected to a five consecutive days dexamethasone treatment to reactivate putative latent virus. Although the magnitude of virus shedding was lower in vaccinated than control calves, all animals re-excreted virus after dexamethasone treatment. This study demonstrates that vaccination of latently infected animals with an inactivated BHV-1 vaccine does not provoke virus re-excretion, and therefore, in our conditions of work, is not considered as a reactivation stimulus.