Tickborne encephalitis virus

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Tick-borne encephalitis (TBE) virus is a member of the genus Flavivirus, and so shares some of the characteristics of yellow fever, dengue and WNV. It causes a meningoencephalitis in humans that has been recognized in Europe since the 1930s, but the disease was referred to differently as Russian spring-summer encephalitis, Far Eastern encephalitis, Taiga encephalitis, biphasic milk fever, Central European encephalitis, Kumlinge disease and other names, even though the cause and clinical course are the same in each case, the aetiology being any one of three closely related subtypes of TBE virus (European, Siberian and Far-Eastern). The disease in humans is biphasic, with a febrile illness lasting 4-10 days followed by meningitis or meningoencephalitis (Haglund & Gunther, 2003). Mild or inapparent infections occur, but in severe cases there is transient or permanent paralysis. Humans become infected by the bite of a tick, Ixodes ricinus or Ixodes persulcatus, or occasionally by consumption of milk from infected animals. TBE may also be spread by mites or mosquitoes. The major vertebrate reservoir hosts of TBE virus are rodents, mainly mice of the genera Apodemus or Clethrionomys, but many other species of domestic animals, birds and even reptiles may be parasitized by I. ricinus and could play a role in transmission. For most hosts, TBE virus is apathogenic. The virus replicates in the tick, which becomes infected during feeding, and the tick remains infected for life (Suss, 2003).

As methods of diagnosis of the disease have improved, involving testing of sera or cerebrospinal fluid for the presence of TBE-specific IgM and IgG antibodies using commercially available kits, the extent of the public health problem posed by TBE has been recognized, with 10000-12000 hospitalized cases annually. Control of tick populations was attempted in Russia but not found to be effective, and since the 1970s, inactivated vaccines have been developed and are available for human use in Europe and Asia (Barrett et al., 2003). In Austria, a high-risk country for TBE, vaccination rates now exceed 90 % in some areas (Kunz, 2003).

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