[Biological properties of tick-borne encephalitis strains isolated in different parts of its geographic range].

A comparative study of over 200 tick-borne encephalitis (TBE) virus strains isolated from patients and ticks in different regions varying in the proportion of severe clinical forms of TBE was carried out. The strains were tested for their pathogenicity for white mice, cytopathic and plaque-forming properties as well as for the interferon-inducing capacity in SPEV cells. All the strains were found to be highly neurovirulent for mice, to produce plaques with diameters varying form less than 1 to 10 mm, and to induce interferon production in SPEV cell. Among the TBE virus strains isolated in the Baltic republics and Vologda region there occurred strains causing complete destruction of SPEV cells at later intervals than the prototype strains. No association of the examined properties of TBE virus strains with the region of isolation or with the clinical forms of human disease was established.