Tick-borne flaviviruses are among the medically most important arboviruses in Europe and Asia. Tick-borne encephalitis causes between 10,000 and 15,000 human cases every year in both continents. Besides this disease there are several other tick-borne flaviviruses which may be of local medical importance, and which are less known, but may be important as differential diagnosis. Among them are louping-ill disease which is present mainly on the British Islands, Omsk hemorrhagic fever, which is prevalent in parts of Russia, Kyasanur Forest Disease, which is distributed in parts of India, Alkhumra hemorrhagic fever, occurring in Saudi Arabia, Powassan encephalitis, which is known to be the only tick-borne flavivirus of human pathogenicity so far detected in North America and some other flaviviruses. Most of these viruses are also more or less important for veterinary medicine. Several other tick-borne flaviviruses so far have neither been associated with human nor animal diseases, and their potential pathogenicity for humans and animals is unknown. Changes in human behaviour, land use, or climate may change the actual geographical distribution and transmission intensity so that tick-borne flaviviruses are potential winners of the changing environment and may increase in medical and veterinary importance.
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