Characterization of Canine Distemper Viruses Adapted to Neural Cells and Their Neurovirulence in Mice

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Abstract
Interaction of the Onderstepoort strain of canine distemper virus (CDV) with 3 established human neural cells, i.e., IMR-32 neuroblastoma, 118-MGC glioma and KG-1 oligodendroglioma, was examined; adaptation of CDV to these cells was attempted. The unadapted virus grew at relatively low titers in the 3 neural cells inducing moderate to minimal cytopathic effects (CPE). The virus was successfully grown at high titers in these cells after 8-10 passages. Biological characteristics such as growth rate, morphology of CPE and plaque size changed after adaptation. Analysis by SDS-polyacrylamide gel electrophoresis failed to show any difference in the MW of component proteins among the unadapted and 3 adapted viruses. The inbred DDD strain of mice developed clinical signs after intracerebral inoculation with the unadapted virus; most of them survived with histological lesions of encephalitis. Neuroblastoma-adapted virus induced only transient clinical signs in some animals with mild encephalitic lesions in the gray matter. Increases in neurovirulence were found for viruses adapted to glioma and oligodendroglioma cells. Almost all mice inoculated with these 2 viruses at 3 wk of age died within 8 days with histological lesions consisting of hyperemia, edema, severe degeneration of nerve cells and a few giant cells. Demyelinating lesions in the absence of inflammatory changes were observed in the cerebellum, pons and medulla oblongata of animals inoculated with oligodendroglioma-adapted virus.