Mondo Description Tick-borne encephalitis is caused by an arbovirus of the Flaviviridae family (tick-borne encephalitis virus, TBEV), transmitted principally by the bite of the Ixodes ricinus tick. The symptomology is biphasic, with the initial phase being associated with a flu-like illness and the second phase (occurring in less than 10% of patients) with symptoms of meningitis or, more rarely, meningoencephalitis.