[Changes in the properties of the vaccinia virus isolated in postvaccinal encephalitis]

Properties of 6 isolates of vaccinia virus isolated from the brain and cerebrospinal fluid in postvaccination encephalitis were studied in comparison with 2 production strains of vaccinia virus with which the children had been vaccinated. Significant differences were found between the strains isolated in postvaccination encephalitis and reference virus strains. The plaques produced by the isolates from brain and CSF were larger (and in some isolates had a hemorrhagic pattern). The isolates were highly pathogenic for chick embryos, reproduced more actively in cells of the chorioallantoic membrane of chick embryos at higher temperature of incubation (40 degrees C), more intensively accumulated in the liver and brain of chick embryos at 37 degrees C and 40 degrees C, produced more intensive lesions and necroses in rabbit skin. The isolates were markedly thermostable at 56 degrees C and insensitive to interferon. It is suggested that the increased pathogenicity of the virus is manifested in the presence of altered immune responsiveness of the host.