Isolation and biological characterization of a measles virus-like agent from the brain of an autopsied case of subacute sclerosing panencephalitis (SSPE).

Isolation of a cytopathic agent causing formation of syncytial giant cells in co-cultivated Vero cells from the brain of an autopsied case of subacute sclerosing panencephalitis (SSPE) is reported. The syncytia usually autolyzed from the center after growing to 1 to 2 mm in diameter and then detached from the culture vessels, and finally made macroscopically recognizable round plaques on the monolayer under liquid overlay. The agent was identified serologically as an agent related to measles virus, by both immunofluorescent tests and plaque reduction tests using anti-measles sera. However, the infected cells did not produce either virions or hemagglutinin, and failed to show hemadsorption and hemolysis of African green monkey red cells even after the 55th passage through Vero cells. Newborn mice, adult mice and hamsters showed neurologic signs after intracerebral inoculations of the infected cells, and most of them died from acute encephalitis. Guinea pigs were unsusceptible. From the brain of the animals with neurologic signs, a similar agent to the inoculated one was recovered. The new isolate appears to be a strain closely related to measles virus on the basis of serology, and was designated as SSPE-"Kitaken-1" strain.