Experimental panencephalitis induced in suckling mice by parainfluenza type 1 (6/94) virus. I. Clinical and pathological features.

Intracerebral inoculation of two strains of suckling mice with 6/94 virus, a parainfluenza type 1 virus originally isolated from two patients with multiple sclerosis, produced clinical disease 1-2 weeks after inoculation. Of 528 animals inoculated, 33% died (26% of the ICR strain and 76% of the BALB/c strain) usually between two or three weeks after injection. Animals that recovered appeared to develop normally. Pathological changes were of two types. Initially, there was a necrotizing panencephalitis with virus-specific intracytoplasmic inclusions in choroid and ependymal epithelial cells and neurons. The second major lesion appeared about 6 weeks post inoculation and consisted of a noninflammatory spongiform degeneration of white matter that primarily involved the cerebral hemispheres; a diffuse vacuolar encephalapathy primarily affecting the brain stem; and a persistent minimal inflammation.