Experimental intranasal infection of equine herpesvirus 9 (EHV-9) in suckling hamsters: kinetics of viral transmission and inflammation in the nasal cavity and brain.

Equine herpesvirus 9 (EHV-9), the newest member of the equine herpesvirus family, is a highly neurotropic herpesvirus that induces encephalitis in a variety of animals. To access transmission of EHV-9 in the nasal cavity and brain, a suckling hamster model was developed so that precise sagittal sections of nasal and cranial cavities including the brain could be processed, which proved useful in detecting viral transmission as well as extension of pathological lesions. Suckling hamsters were inoculated intranasally with EHV-9, and were sacrificed at 6, 12, 18, 24, 36, 48, and 60 h post inoculation (PI). Sagittal sections of the entire head, including nasal and cranial cavities including the brain, were made to assess viral kinetics and identify the progress of the neuropathological lesions. At 12 to 24 h PI the virus attached to and propagated in the olfactory epithelium, and infected adjacent epithelial cells. At 48 h PI, immunohistochemistry for EHV-9 viral antigen showed that virus had extended from the site of infection into the olfactory bulb and olfactory nerve. These results indicate that EHV-9 rapidly invades the brain via the olfactory route after experimental intranasal infection.