Reactivation in calves of latent infection by Bovid herpesvirus-4

Nine calves, six of which had been infected with strain 85/BH 16TV and three with strain 85/BH 232TN of Bovid herpesvirus-4 (BHV-4), were treated with dexamethasone (DMS) three months after infection. DMS administration did not induce any clinical signs of disease, but BHV-4 was isolated from the nasal swabbings of all calves for a maximum of 8 days after the start of DMS treatment. The virus was also isolated from the nerve tissues, nasal mucosa, lymph nodes, lung and spleen of 4 calves that were killed at different stages (3, 5, 7 days) of the DMS treatment. Intranuclear inclusions associated with cellular shrinkage were found in the neural tissues of calves killed either 3 or 5 days after the start of DMS treatment. Unexpectedly, a latent infection by infectious bovine rhinotracheitis (IBR) virus was reactivated. The virus was isolated from the nasal swabbings of two calves and also from the brain, cerebellum and nasal mucosa of one calf killed 5 days after the start of DMS treatment.