Bovine Herpesvirus 5 Glycoprotein E Is Important for Neuroinvasiveness and Neurovirulence in the Olfactory Pathway of the Rabbit

Glycoprotein E (gE) is important for full virulence potential of the alphaherpesviruses in both natural and laboratory hosts. The gE sequence of the neurovirulent bovine herpesvirus 5 (BHV-5) was determined and compared with that of the nonneurovirulent BHV-1. Alignment of the predicted amino acid sequences of BHV-1 and BHV-5 gE open reading frames showed that they had 72% identity and 77% similarity. To determine the role of gE in the differential neuropathogenesis of BHV-1 and BHV-5, we have constructed BHV-1 and BHV-5 recombinants: gE-deleted BHV-5 (BHV-5gEΔ), BHV-5 expressing BHV-1 gE (BHV-5gE1), and BHV-1 expressing BHV-5 gE (BHV-1gE5). Neurovirulence properties of these recombinant viruses were analyzed using a rabbit seizure model (S. I. Chowdhury et al., J. Comp. Pathol. 117:295–310, 1997) that distinguished wild-type BHV-1 and -5 based on their differential neuropathogenesis. Intranasal inoculation of BHV-5 gEΔ and BHV-5gE1 produced significantly reduced neurological signs that affected only 10% of the infected rabbits. The recombinant BHV-1gE5 did not invade the central nervous system (CNS). Virus isolation and immunohistochemistry data suggest that these recombinants replicate and spread significantly less efficiently in the brain than BHV-5 gE revertant or wild-type BHV-5, which produced severe neurological signs in 70 to 80% rabbits. Taken together, the results of neurological signs, brain lesions, virus isolation, and immunohistochemistry indicate that BHV-5 gE is important for efficient neural spread and neurovirulence within the CNS and could not be replaced by BHV-1 gE. However, BHV-5 gE is not required for initial viral entry into olfactory pathway.