ISOLATION OF TICK-BORNE ENCEPHALITIS VIRUS FROM DERMACENTOR PICUS HERM. AND IXODES PERSULCATUS P. SCH. TICKS IN PLACES OF THEIR MUTUAL HABITATION,

Abstract : The observations were conducted in one station of the forest steppe zone in western Siberia in the vicinity of the town Ishim. The station is in an area in which the main trees are birch and aspen, and the lower forest layers are the same species. The grass is moderate by dense. Two species of ixodid ticks were found - D. pictus and I. persulcatus. Observations on the prevalence of ticks conducted over 10 day periods from 20 April to 30 September 1963, showed D. pictus to be the chief species. The maximum number of adults of D. pictus adults collected by blanket dragging per one kilometer was 18 in the first ten days of May. The maximum number of I. persulcatus under similar conditions was not more than 7. For isolation purposes, 560 hungry adult D. pictus and 1220 I. persulcatus were taken. A total of 178 tests was made (10 ticks per test); of them, 56 were D. pictus and 122 were I. persulcatus. The viruses were isolated in white mice by intercerebral inoculation with suspensions of ticks with 3 to 5 successive passages and in human embryo fibroblasts with Coxsaki A21 as an indicator. A total of 40 strains of tick-borne encephalitis virus (32.8%) were isolated from I. persulcatus ticks and 7 strains from D. pictus (12.5%). All viruses were found to be pathogenic for white mice by the intercerebral and peripheral routes of inoculation. The index of invasivness (1 g LD50) was 0.3 to 5.0. It was concluded that D. pictus ticks are one of the reservoirs of tick-borne encephalitis virus. (Author)