Thirty percent of weanling rats infected with JHM murine corona virus developed a subacute demyelinating encephalomyelitis approximately 3 weeks after intracerebral inoculation. Small demyelinating foci were located in the deep cerebral white matter and large, sharply demarcated demyelinating lesions were detectable in optic chiasma, pons and spinal cord. Axons as well as neurons were well preserved in the demyelinating plaques in areas where the lesions extended to the gray matter. Perivascular cuffings, consisting of plasma cells and mononuclear cells, were frequently found.

Viral antigen was found mostly in the white matter and in glial cells, leaving neurons unstained. Electron microscopic studies of the early lesions of white matter disclosed two different kinds of cell degeneration which developed prior to the myelin disruption and mononuclear cell infiltration. One was a small pyknotic cell, which is thought to be an oligodendrocyte and the other is a ballooned cell containing abundant microtubules. Virus particles could be demonstrated only in the latter cell type. Discussion about astrocytes as well as oligodendrocytes was made in relation to the initial stage of demyelination caused by virus infection. This animal model may be useful in the analysis of the mechanisms leading to demyelination in subacute or chronic infections.