Experimental infection of neonatal calves with neurovirulent bovine herpesvirus type 1.3.

A type of bovine herpesvirus, BHV-1.3, causes encephalitis in calves, whereas BHV-1.1 causes respiratory disease. Three colostrum-deprived calves and two colostrum-fed calves were inoculated with BHV-1.3 by intranasal aerosolization. Two colostrum-deprived calves were inoculated with BHV-1.1 by intranasal aerosolization. BHV-1.3-inoculated calves demonstrated severe encephalitis with minimal respiratory lesions, and BHV-1.1-inoculated calves demonstrated severe respiratory lesions and no clinical signs of neurologic disease. Calves fed colostrum that contained virus neutralizing antibodies were protected against neurologic disease. Colostrum-fed BHV-1.3-inoculated calves did not develop disease although they did become infected; virus was shed in respiratory secretions for 10-13 days postinoculation, similar to infected colostrum-deprived calves. BHV-1.3 was reactivated from a latent state from one colostrum-fed calf after administration of dexamethasone 60 days postinoculation. Histopathologic examination of the three colostrum-deprived BHV-1.3-inoculated calves revealed severe lesions of encephalitis. One of the two BHV-1.1-inoculated calves had one focal lesion of encephalitis. Virus was isolated from brain tissue of colostrum-deprived BHV-1.3-inoculated calves and from one BHV-1.1-inoculated calf. Immunohistochemical staining for BHV-1 antigen was observed in neurons from the colostrum-deprived BHV-1.3-inoculated calves.