Distribution of Ixodes ricinus and I. persulcatus ticks in southern Karelia (Russia).

The northern boundary of the sympatric zone of Ixodes persulcatus and I. ricinus (Acari: Ixodidae) passes through Karelia. Studies carried out in the 1950s showed that these Ixodes species were mostly found in southern Karelia.

Different tick-borne encephalitis virus (TBEV) prevalences in unfed versus partially engorged ixodid ticks--evidence of virus replication and changes in tick behavior.

There is some evidence that tick-borne encephalitis virus (TBEV) prevalence in ticks, removed from humans, is higher than that in field-collected ticks from the same area. There are two possible explanations: (i) Infected ticks are more active and aggressive and can be found on humans more often. (ii) Some questing ticks are infected with TBEV in a low, undetectable concentration; during tick feeding, virus replicates and reaches the titers that can be detected.

Microevolution of tick-borne encephalitis virus in course of host alternation.

Two tick-borne encephalitis (TBE) virus variants were studied: mouse brain-adapted strain EK-328 and its derivate adapted to Hyalomma marginatum ticks. The tick-adapted virus exhibited small-plaque phenotype and slower replication in PEK cells, higher yield in ticks, decreased neuroinvasiveness in mice, increased binding to heparin-sepharose. A total of 15 nucleotide substitutions distinguished genomes of these variants, six substitutions resulted in protein sequence alterations, and two were in 5'NTR.