[Changes in the host-dependent characteristics of the tick-borne encephalitis virus during its adaptation to ticks and its readaptation to white mice].

Features of multiplication in pig embryo kidney (PEK) cells of a variant of tick-borne encephalitis (TBE) virus previously selected by passages in H. plumbeum ticks and changes in the properties of the variant upon its repassages in white mouse brains were studied. The tick-adapted TBE variant differed from the original strain in the following characteristics: a lower yield of infectious virus and physical virus particles, altered time-course of infectious virus release from the cell, the lack of virions moving towards cathode in rocket immunoelectrophoresis (RIEP), reduced hemagglutinating activity of the virus, small plaque size in PEK culture, reduced level of virus replication in white mouse brain at a high cytopathic activity of the virus, and low synthesis of virus particles moving towards anode in RIEP. The acquired characteristics were stable at the level of 3 passages in white mice. In the course of further readaptation to these animals the virus recovered its capacity for synthesis of "cathode" virions in PEK cell culture, differing from the original strain by a higher level of virus reproduction in mammalian cells, altered electrophoretic mobility of the structural virion protein V1, and plaque size.