The mouse hepatitis virus strain JHM was injected intracerebrally into newborn and weanling rats. Three types of diseases were observed: 1. Acute panencephalitis: Almost all suckling rats became moribund within 6 days. Histologically severe panencephalitis with demyelinating foci was noticed; the foci were similar to those found in mice. Virus was easily detectable in the oligodendroglial cells and neurons both by immunofluorescence and electron microscopy. Infectious virus could be isolated. 2. Subacute demyelinating encephalomyelitis (SDE): Three weeks after infection of weanling rats, about 35% of the animals developed paralysis. Neuropathologically, demyelination with a striking predilection for white matter was observed in the brain stem, optic nerve and spinal cord. Virus was detectable by electron microscopy in degenerating oligodendroglial cells only, which corresponded to the results obtained by the immunofluorescent techniques. Infectious virus could be recovered. 3. Chronic progressive paralysis: Inoculated weanling rats without SDE developed 6 to 8 months later a slowly progressing paralysis of the legs. Hydrocephalus and myelomalacia were present. Viral "footprints" could not be detected.
Early and late CNS-effects of corona virus infection in rats.