[Attenuated variants of the tick-borne encephalitis virus complex].

The paper presents the results of the study of 8 attenuated strains of viruses of the tick-borne encephalitis complex by the marker of pathogenicity for Syrian hamsters in comparison with virulent virus strains. The group of the attenuated strains was found to be nonhomogeneous in this marker of pathogenicity for Syrian hamsters. One of the 8 strains, Pan-114, proved to be highly virulent for these animals by the intracerebral route. The analysis of the experimental results and data from the literature shows the degree of pathogenicity of attenuated strains to differ for mice, Syrian hamsters and monkeys, apparently indicating that each virus variant is attenuated only for a given species of laboratory animals.