ISOLATION OF A MEASLES-VIRUS VARIANT - PROTECTION OF NEWBORN MICE FROM MEASLES ENCEPHALITIS BY 24 H PRIOR INTRACEREBRAL INOCULATION WITH THE VARIANT

A small plaque mutant with reduced neurovirulence in newborn mice was obtained from Edmonston strain measles virus after propagation for 5 m onths in NIH3T3 cells. It retained the antigenicity of the parental vi rus and tended to induce higher neutralizing antibody titers in the ad ult BALB/c mice. The intracerebral (but not intraperitoneal) inoculati on of the live mutant virus one day before prevented the newborn BALB/ c mice from encephalitis caused by the intracerebral challenge with th e parental strain at a dose of 10-20 LD50. The intracerebral inoculati on with the mutant virus whose replication capacity was inactivated by UV-irradiation was ineffective. The protection was not attributed to interferons nor to viral interference. The mechanism remains unknown.