Viraemia in Clethrionomys glareolus -- a new ecological marker of tick-borne encephalitis virus.

Viraemia was studied in adult Clethrionomys glareolus subcutaneously infected with 12 strains of tick-borne encephalitis (TBE) virus isolated in western and eastern foci of TBE. Nine strains caused viraemia regularly or irregularly, reaching titres higher than the threshold level of TBE virus infectivity for its vectors, ixodid ticks (2.5 -- 4.5 log LD50/0,03 ml) and three strains caused lower levels of hiraemia (0.4 -- 1.5 log LD50/0.03 ml). The ability or inability of various TBE virus strains to cause viraemia in adult C. glareolus in titres higher than the threshold level of infectivity for tick vectors was considered as an ecological marker of TBE virus. This marker was designated Cg: Cg+ and Cg- for TBE virus strains inducing respectively higher and lower levels of viraemia than the threshold of infectivity.