Abstract
Human infections with tick-borne encephalitis (TBE)virus are a public health concern in certain regions of Europe, central and eastern Asia. Expansions of endemic areas and increased incidences have been associated with different factors including ecological changes supporting tick reproduction, socioeconomic changes increasing human outdoor activities and climatic changes favouring virus circulation in natural foci. Austria is among the most strongly affected countries in Central Europe, but the annual number of cases has strongly declined due to vaccination. Here,we have analysed changes of the incidence of TBE in the unvaccinated population of all federal states of Austria over a period of 42 years. The overall incidence in Austria has remained constant, but new strongly affected endemic regions have emerged in alpine valleys in the west of Austria. In parallel, the incidence in low-land regions in the north-east of the country is decreasing. There is no evidence for a shift to higher altitudes of infection sites in the traditional TBE zones,but the average altitudes of some newly established endemic areas in the west are significantly higher. Our analyses underscore the focal nature of TBE endemic areas and the potential of TBE virus to emerge in previously unaffected regions.
Highlights
Tick-borne encephalitis (TBE) virus is endemic in many parts of Europe as well as central and eastern Asia and responsible for more than 10,000 hospitalised TBE patients every year [1]
We have addressed the question of possible regional changes of TBE endemicity by analysing the incidences of TBE in the unvaccinated population over a period of 42 years (1972 to 2013) in all federal states of Austria
In the past two to three decades, the most remarkable change in TBE incidence in Austria was caused by vaccination, resulting in an 84% reduction of the annual number of cases, while the incidence in the unvaccinated population remained constant at ca 6 per 100,000 population [6]
Summary
Tick-borne encephalitis (TBE) virus is endemic in many parts of Europe as well as central and eastern Asia and responsible for more than 10,000 hospitalised TBE patients every year [1]. There is strong evidence that conditions allowing non-viraemic transmission from infected larvae to non-infected nymphs by co-feeding on the same rodent are a major prerequisite for the maintenance of virus circulation in nature [8] Such a mechanism of tick infection requires specific climatic conditions (especially a swift rise of temperature in spring) that lead to a temporal coincidence of larval and nymph development and possibly contribute to the restriction of TBE virus to selected endemic regions. This is in contrast to other tick-transmitted pathogens such as Borrelia burgdorferi that are found in all areas populated with ticks [9,10,11,12]
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