[Structure of tick-borne encephalitis virus populations in foci with various levels of morbidity in the human population].

The results of comparative studies on the structure of viral populations by virulence for white mice inoculated by different routes as well as on the antigenic characteristics of virus strains in two foci of tick-borne encephalitis (TBE) in Western Siberia differing significantly by the disease incidence rates among the human population and by the "risk of infection" indices are presented. The portion of virus strains with different virulence in the total number of strains (92) studied in both TBE foci under comparison did not differ significantly. Virus strains antigenically differing from the known prototype TBE virus variants (persulcatus and ricinus) and at the same time representing antigenically homogeneous group were found to be circulating in Western Siberia natural TBE foci.