Replication of tick-borne encephalitis (TBE) virus in Ixodes ricinus ticks.

The influence of external factors on virus carriage of Ixodes ricinus ticks in laboratory and in nature was studied. In laboratory experiment, only one nymph was positive for the presence of virus on 120th day after metamorphosis. The virus titer was 10(2) mouse i.c. LD50/0.03 ml. Transmission experiments were negative. The nymphs were positive on 75th, 111th and 159th day after metamorphosis, always chilling in the field experiment. The titres of virus varied from the lowest detectable amount value to 10(3.6) mouse i.c. LD50/0.03 ml. The transmission of virus was positive in two cases.