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

Calves were inoculated with the bovine herpes virus 1 (BHV-1) vaccine strai n (RLB 106), which is a temperature sensitive mutant. The route of inoculat ion was intranasal instillation or intramuscular (IM) injection (flank or n eck). As a control, five calves were given placebo by IM injection of the n eck. Regardless of the infection route, clinical symptoms did not occur. Ho wever, BHV-1 neutralizing antibodies were detected after inoculation demons trating that sere-conversion occurred. At 60 days post-inoculation, dexamet hasone was given by IM injection to attempt reactivation of RLB 106, Only t hose calves inoculated by the intranasal route shed virus leading to an inc rease in BHV-1 specific antibodies. As expected, viral DNA and the latency related-RNA were detected in trigeminal ganglia (TG) of calves inoculated b y the intranasal route. In contrast, viral nucleic acid was not detected in TG of calves inoculated by the IM route or in calves inoculated with place bo. In cervical ganglia or sacral dorsal root ganglia, viral nucleic acid w as not consistently detected. This study provides evidence that efficient l atency and reactivation does not occur following IM inoculation. Since seru m-neutralizing antibodies were detected in all inoculated calves, IM inocul ation led to sere-conversion. (C) 2000 Elsevier Science Ltd. All rights res erved.