PROPERTIES OF A CYTOPATHIC AGENT ISOLATED FROM A PATIENT WITH SUBACUTE SCLEROSING PANENCEPHALITIS IN JAPAN

A cytopathic agent isolated from the brain biopsy of a patient with subacute sclerosing panencephalitis (SSPE) was investigated. The agent could most easily be maintained by cocultivation of infected cells with fresh Vero cells (cercopithecus monkey kidney line) . Cytopathogenicity consisting of macroscopically recognizable round syncytia (plaques) appeared on the monolayer under liquid overlay. So far up to the 60th passage level, no cell-free virus has been obtained under various conditions. Antigenicity of measles virus was demonstrated by the immunofluorescence tests and by the plaque reduction tests using specific measles virus antiserum. In addition, electron microscopic findings of paramyxovirus nucleocapsids in the infected cells, hemadsorption of cercopithecus monkey erythrocytes and propagation characteristics in the presence of actinomycin D and of 5-bromodeoxyuridine were consistent with those of measles virus. That the nucleocapsids were abundant in the nuclei and much fewer in the cytoplasm is compatible with the data on SSPE viruses reported by others. Adult guinea pigs, mice and hamsters developed neurological symptoms by intracerebral inoculations of the agent and deaths ensued in most of the animals. Freezing storage with dimethyl sulfoxide at -70C was able to preserve the infected cells for a long period just as with uninfected Vero cells. This may suggest a temperate association of the agent with host cells and nonrecovery of cell-free virus.