Chronic central nervous system demyelination in mice after JHM virus infection.

The pathogenesis of murine hepatitis virus, strain JHM, was studied in 6- and 12-week-old C57/BL mice. There was 100% mortality in the 6-week-old mice after intracerebral inoculation. The lesions were characterized by necrotizing encephalomyelitis, without demyelination. Intracerebral inoculation of 12-week-old animals, however, resulted in no morbidity or mortality. The 12-week-old animals showed transient virus replication in the brain, spinal cord, and liver, which was cleared by day 14. Histologic examination showed evidence of ongoing demyelination, concomitant remyelination, and hydrocephalus ex vacuo. Although viral antigen was demonstrated by immunofluorescence in the central nervous system of these animals, no infectious virus was recovered, and immunosuppression regimens did not potentiate the disease.