Comparative pathogenesis of acute and latent infections of calves with bovine herpesvirus types 1 and 5

This study was conducted to compare the pathogenesis of acute and latent in fections with closely related bovine herpesvirus types 1 (BHV-1) and 5 (BHV -5) in their natural host. Two groups of eight calves were inoculated intra nasally with BHV-1 or BHV-5. Although BHV-1 and BHV-5 similarly replicate i n the nasal mucosa after inoculation, both viruses differ markedly in their ability to cause disease, BHV-5 being responsible of some fatal encephalit is while BHV-1 inducing rhinotracheitis. Virus isolation and immunohistoche mistry demonstrated that BHV-5 replicates extensively in neurons of the cen tral nervous system (CNS) and in respiratory cells of lungs, tracheal and n asal mucosae. Invasion of the CNS likely occurs through the trigeminal and olfactory pathways. Both groups developed cross-neutralising antibodies dur ing this experiment suggesting partial clinical cross-protection afforded b y the two infections. Three months after primary infection, experimental re activation showed that BHV-5 was able to establish latency in the trigemina l ganglia but also the CNS of surviving calves. Moreover, laboratory findin gs suggested that BHV-5 could also persist in the tracheal and nasal mucosa e. These results indicate that, after primary infection, BHV-1 and BHV-5 di splayed similar biological features and consequently need to be considered together for the control of BHV-1 infection.