Experimental parainfluenza-type-1-virus-induced encephalopathy in the adult mouse. An ultrastructural study of early lesions.

The adult mouse inoculated intracerebrally with 6/94 strain of parainfluenza type 1 virus developed selective degenerative lesions in cerebral white matter. Ultrastrucrally, the infiltration of mononuclear cells, mostly lymphoid cells, apparently preceded the alterations of white matter parenchyma. The prominent feature of the white matter lesion was a lytic degeneration of both axon and myelin that seemed to be triggered by the mononuclear cell infiltration. Nucleocapsids of paramyxovirus were found only in ependymal cells and the very early stages of the infection. It is suggested that the mechanism of the white matter degeneration might be that of a virus-induced cell-mediated immune response directed at both the axon and myelin.