A gE-negative bovine herpesvirus 1 vaccine strain is not re-excreted nor transmitted in an experimental cattle population after corticosteroid treatments.

To study possible reactivation and to quantify subsequent transmission of a live gE-negative bovine herpesvirus 1 (BHV1) vaccine strain in cattle populations, four experiments were performed. Two groups of cattle were each tested twice for the possibility of reactivation. Inoculation with a gE-negative BHV1 vaccine was done either intramuscularly or intranasally and treatment with corticosteroids in an attempt to reactivate vaccine virus, was done after 6 or 11 weeks, and again after 6 months. To quantify transmission of vaccine virus following possible reactivation, each cattle was housed together with one susceptible contact-cattle. Contact-infections were monitored using virus shedding and antibody responses. After corticosteroid treatments, re-excretion of virus was never detected in cattle that had been inoculated with the gE-negative BHV1 vaccine strain. Contact cattle did not shed gE-negative BHV1, nor mounted any antibody response against BHV1. In contrast, positive control cattle, inoculated intranasally with wild-type BHV1, re-excreted virus in high titers in nasal fluids and transmitted the virus to contact cattle. Based on these results, the transmission ratio R(0) of the vaccine strain was zero. We concluded that it is highly unlikely that the live gE-negative BHV1 vaccine strain will be re-excreted after possible reactivation, and consequently, it is even less likely that reactivated vaccine virus will spread in the cattle population.