Abstract
The geographical risk areas for tick-borne encephalitis (TBE) in Finland remained the same until the beginning of the 21st century, but a considerable geographical expansion has been observed in the past 10 years. In order to support public health measures, the present study describes the number of laboratory-confirmed TBE cases and laboratory tests conducted and the associated trends by hospital district, with a particular emphasis on the suspected geographical risk areas. An additional investigation was conducted on 1,957 clinical serum samples throughout the country taken from patients with neurological symptoms to screen for undiagnosed TBE cases. This study identified new TBE foci in Finland, reflecting the spread of the disease into new areas. Even in the most endemic municipalities, transmission of TBE to humans occurred in very specific and often small foci. The number of antibody tests for TBE virus more than doubled (an increase by 105%) between 2007 and 2013. Analysis of the number of tests also revealed areas in which the awareness of clinicians may be suboptimal at present. However, it appears that underdiagnosis of neuroinvasive TBE is not common.
Highlights
Tick-borne encephalitis virus (TBEV) is a clinically important flavivirus causing encephalitic disease with thousands of cases annually in Europe [1]
The European subtype is mainly carried by Ixodes ricinus ticks in central and north-eastern Europe, whereas the other two are mainly found in I. persulcatus ticks in an area reaching from north-eastern Europe to the Russian Far East, China and Japan [2]
In order to further support public health measures, we describe the number of laboratory-confirmed tick-borne encephalitis (TBE) cases and of conducted laboratory tests as well as the associated trends for each of the 21 Finnish hospital districts, with a particular emphasis on the suspected risk areas
Summary
Tick-borne encephalitis virus (TBEV) is a clinically important flavivirus causing encephalitic disease with thousands of cases annually in Europe [1]. There are three known subtypes of TBEV: European (Eur), Siberian (Sib) and Far-Eastern (FE). The European subtype is mainly carried by Ixodes ricinus ticks in central and north-eastern Europe, whereas the other two are mainly found in I. persulcatus ticks in an area reaching from north-eastern Europe to the Russian Far East, China and Japan [2]. TBEV is maintained in nature by ticks and their hosts. Ticks serve both as a reservoir and as vector for the virus [3]. Ixodes ticks are widely spread generalist ectoparasites [6]. Circulation of TBEV is dependent on the local vegetation, dynamics of the vertebrate and tick host populations and microclimatic conditions, leading to focal occurrence of TBEV within the distribution area of the host ticks [3]
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