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 popu lations, four experiments were performed. Two groups of cattle were each te sted twice for the possibility of reactivation. Inoculation with a gE-negat ive BHV1 vaccine was done either intramuscularly or intranasally and treatm ent with corticosteroids in an attempt to reactivate vaccine virus, was don e after 6 or 11 weeks, and again after 6 months. To quantify transmission o f vaccine virus following possible reactivation, each cattle was housed tog ether with one susceptible contact-cattle. Contact-infections were monitore d using virus shedding and antibody responses. After corticosteroid treatme nts, re-excretion of virus was never detected in cattle that had been inocu lated with the gE-negative BHV1 vaccine strain. Contact cattle did not shed gE-negative BHV1, nor mounted any antibody response against BHV1. In contr ast, 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 th e 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 re activation, and consequently, it is even less likely that reactivated vacci ne virus will spread in the cattle population. (C) 2000 Elsevier Science Lt d. All rights reserved.