Isolation of tick-borne encephalitis virus from Ixodes ricinus ticks in the Tribec region.

An attempt has been made to isolate the tick-borne encephalitis virus from nymphs and adults of the tick Ixodes ricinus in the Tribec region. In 1963 no virus was found in 2715 nymphs and 998 adults from various parts of the region, but in 1964, from 2153 unfed ticks collected in the spring, two strains of virus were isolated from the 798 nymphs and two from the adults (one from 647 males and one from 708 females). Thus, on average, 0.2% of the ticks in the region were infected; in the elementary foci of Topol'cianky and Jelenec, where the virus-containing ticks were found, the proportion varied between 0.4% and 0.8%. In 1964 no viruses having a cytopathic effect on chick-embryo-cell cultures were isolated from I. ricinus ticks, in contrast to the isolation of nine such strains in the previous year. The significance of these results in relation to the interstadial transmission of tick-borne encephalitis virus is discussed.