Analysis of latency in cattle after inoculation with a temperature sensitive mutant of bovine herpesvirus 1 (RLB106)

Calves were inoculated with the bovine herpes virus 1 (BHV-1) vaccine strain (RLB 106), which is a temperature sensitive mutant. The route of inoculation was intranasal instillation or intramuscular (i.m.) injection (flank or neck). As a control, five calves were given placebo by i.m. injection of the neck. Regardless of the infection route, clinical symptoms did not occur. However, BHV-1 neutralizing antibodies were detected after inoculation demonstrating that sero-conversion occurred. At 60 days post-inoculation, dexamethasone was given by i.m. injection to attempt reactivation of RLB 106. Only those calves inoculated by the intranasal route shed virus leading to an increase in BHV-1 specific antibodies. As expected, viral DNA and the latency related-RNA were detected in trigeminal ganglia (TG) of calves inoculated by the intranasal route. In contrast, viral nucleic acid was not detected in TG of calves inoculated by the i.m. route or in calves inoculated with placebo. In cervical ganglia or sacral dorsal root ganglia, viral nucleic acid was not consistently detected. This study provides evidence that efficient latency and reactivation does not occur following i.m. inoculation. Since serum-neutralizing antibodies were detected in all inoculated calves, i.m. inoculation led to sero-conversion.