[Detection of the natural heterogeneity of natural populations of tick-borne encephalitis viruses and a grouping of the strains]

Eighty strains of tick-borne encephalitis virus isolated from I. persulcatus ticks collected in 1976-1981 in the same biotopes in the south and north of the zone of coniferous-broad-leaved forests, and two biotopes of the southern taiga subzone of the Khabarovsk region and Sakhalin island, as well as from the brains of fatal cases were studied. Significant differences were found between maximal and minimal values of the invasive activity in spatially separated populations of the same zone (t = 2.32, P less than 0.02). Significant interpopulation differences were also found in the value of peripheral activity (t = = 2.77, P less than 0.02) and invasivity index (t = 3.83, P less than 0.01). Natural heterogeneity of the strains was found both by previously known markers (high neurovirulence for mice, invasivity index, plaque size in SPEV cell culture, viremia in mice, stability to thiamine 10X- and a new marker proposed by us: the degree of adsorption of hemagglutinins on an ion-exchanger DEAE-Sephadex A-50. Strains of tick-borne encephalitis virus were grouped in two landscape zones, this grouping indicated the existence of significant interpopulation differences.