Modification of Venezuelan equine encephalomyelitis virus infection in mice by X radiation.

A highly virulent strain of Venezuelan equine encephalomyelitis (VEE) virus produced less severe histopathologic changes in brain tissues of mice previously exposed to sublethal total-body x-irradiation than it caused in nonirradiated mice. Prior exposure to 600 R of x-irradiation virtually eliminated the lesions of vasculitis and encephalitis that were found in the infected nonirradiated control mice. Mean peak brain lesion scores generally decreased as radiation exposure dose was increased. Irradiation of mice before inoculation often decreased median time to death, whereas the severity of pathologic changes in brain tissues from inoculated irradiated mice was often reduced, without significantly altering ultimate host survival. The inflammatory response did not appear to have a significant role in clearance of this virus from the brain. There was no evidence that participation of the immune response contributed to total mortality from VEE virus encephalitis, as indicated by the failure of radiation immunosuppression to reduce mortality. Death apparently was caused by the direct cytocidal effects of VEE virus replication.