Inclusion Criteria:  Patient: The patients diagnosed with acute infection with TBEV at admission. Control: same age (plus/minus 4 years), level of education (plus minus 2 years) and the same gender as patient.  Exclusion Criteria:  Patient: Patients who turn out to have different diagnose than acute infections with TBEV. Control: Previously infection with tick-borne encephalitis virus. The patients who were diagnosed with typical symptoms and only TBEV IgM-test must take a blood sample for IgG analyses. If the TBE IgG analysis is negative, the patient will be excluded.