Specific clinical and epidemiological features of tick-borne encephalitis in Western Siberia.

In Western Siberia, tick-borne encephalitis (TBE) morbidity among residents of all ages and social groups has remained high over many years. The frequency of tick bites is high, and 2.6-5.7% of bitten persons are hospitalized each year because of suspected TBE infection. According to official statistical data, children <14 years account for 20-30% of TBE cases. Adult, working-age people (20-49 years) are at highest risk of infection. TBE may progress in a febrile, meningeal, or focal (paralytic) form, becoming chronic in 1-1.7% of cases. Severe progression and fatal outcomes of the disease have been recorded in all age groups. Over the past 20 years, mortality varied from 1.8% to 3%, increasing in periods of high TBE morbidity. This data stresses the necessity for more effective measures aimed at preventing TBE infection in the region. The results of our analyses of TBE peculiarities in Western Siberia lead to the conclusion that people in that region have been at high risk of infection and developing the most complicated forms of TBE.