Encephalitis induced by bovine herpesvirus 5 and protection by prior vaccination or infection with bovine herpesvirus 1

Calves were intranasally challenged with bovine herpesvirus 5 (BHV5) and fo llowed for the development of viral infection, clinical encephalitis, histo logic lesions in the brain, and viral sequences in the trigeminal ganglia. Calves that were previously vaccinated with bovine herepesvirus 1 (BHV1, n = 4) or previously infected with BHV1 (n = 5) or that had not been exposed to either virus (n = 4) were compared. No calf developed signs of encephali tis, although all calves developed an infection as indicated by nasal secre tion of BHV5 and seroconversion to the virus. Histologic lesions of encepha litis consisting of multifocal gliosis and perivascular cuffs of lymphocyte s were observed in calves not previously exposed to BHV1. BHV5 sequences we re amplified from the trigeminal ganglia of calves previously vaccinated an d from calves not previously exposed to BHV1; calves sequentially challenge d with BHV1 and later BHV5 had exclusively BHV1 sequences in their trigemin al ganglia. Administration of dexamethasone 28 days after BHV5 challenge di d not influence clinical disease or histologic lesions in either previously unexposed calves (n = 2) or previously immunized calves (n = 2), although it did cause recrudescence of BHV5, as detected by nasal virus secretion.