Neural changes in recurrent infection of infectious bovine rhinotracheitis virus in calves treated with dexamethasone.

Recurrent infection by infectious bovine rhinotracheitis (IBR) virus was induced in calves by dexamethasone (DM) treatment (given 5 days) at 5 months after primary infection. The virus appeared in nasal secretions of the calves on the 4th day after initiation of DM treatment and continued until the 9th day. The calves were killed on the 1st, 3rd, 4th, 5th, 6th, 7th, 8th, 10th, and 11th days after DM treatment was started for examination by histopathologic and immunofluorescent antibody techniques. The most significant neural change was trigeminal ganglionitis with neuronophagia, which was observed from the 3rd to the 11th day. Significantly, the extent of changes in the trigeminal ganglion and medulla oblongata corresponded to the amount of DM treatment administered. The IBR virus antigen was first observed in the trigeminal ganglion cells, and thereafter, it was detected in the Schwann cells, satellite cells, neuroglia cells, and nasal mucosa until the 10th day. These observations indicate that the IBR virus is capalbe of producing a persistent infection in the trigeminal ganglion and that trigeminal ganglionitis may be a characteristic lesion for inducing the reactivation of lagent IBR virus.