Page 205 - TBE_Book_V2_2019

Chapter 11: General epidemiology of TBE

Table 3: Seroprevalence of anti-TBE anti- According to phylogenetic data, TBEV-EU is
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bodies in wild animals in different Euro- the youngest of all TBEV subtypes. These
pean countries data indicate that about 3,000 years ago the
European strain diverged from the ancestor
Preva- virus and migrated westwards. Some evidence
Country Vertebrate Literature
lence (%) suggests that the TBEV strains in Central
Europe originated in the Czech Republic. From
Bornholm
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Archipel Deer 83 Freundt there the virus migrated about 350 years ago
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(Denmark) to Germany. Several waves of spreading and
migration seem to have occurred. In Germany
Aland Ar- intensive studies on particular TBE foci show
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chipel Rodents 0.5 Han et al.
(Finland) that in each TBE focus, a particular and clearly
identifiable virus strain is prevalent. The TBEV
Yellow-
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Austria necked 47.9 Labuda et al. strains seem to be stable in their E gene
mouse sequences for decades as shown in Finland
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Austria Bank voles 29.4 Labuda et al. (Kumlinge strain) and in Austria (Zillertal
9
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Slovakia Deer 35.3 Labuda et al. strain). However, no clear pattern of viral
spread exists that can be correlated to
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Slovakia Boar 36.8 Labuda et al.
landscapes or to human activities to explain
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Slovakia Rodents 14 Labuda et al. the introduction of the Siberian and Far-
Czech Rodents 14.6 Gresikova et. al. Eastern subtypes in the Baltic region. Analysis
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Republic of the E genes of TBEVs from different strains

shows a kind of geographic clustering e.g. in
only recently, coincidentally with the con- Scandinavia, Germany, the Czech Republic or
struction of the Transsiberian Highway and the the Slovak Republic (Slovakia). But there are
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Transsiberian Railway. Also, the European also some strains that are genetically related
sub-type has been detected in South Korea to strains from greater distances, e.g. German
and also in Siberia. 13,14 Improved understand- strains that are similar to Russian or
ing of the phylogeography of these strains will Scandinavian strains. It is unclear at the
require additional studies. moment whether these genetic relationships
are due to missing link strains. A clear
European subtype classification of European strains into genetic
clusters or branches is still missing and awaits
The European subtype (formerly known as the the analysis of more strains from different
“Western subtype”) of TBEV is prevalent in parts of Europe.
Europe. However, the distribution ranges from
France and The Netherlands at its western The phylogenetic analysis of TBEV-EU is
limit of distribution to South Korea, the unclear and confusing. For about 3,000 years,
easternmost region where TBEV-EU has been when the European strain branched off from
detected so far. 9,13,15 While only TBEV-EU is the ancestor virus and migrated westward,
found in Central Europe, more than 80% of TBEV-EU appears to have remained mono-
identified strains in the Baltics belong to the phylogenetic. All currently known strains from
European subtype. In Western and Eastern Central Europe divided only about 300 to 400
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Siberia, only a low percentage (<10%) of the years ago. In contrast to the Siberian
identified TBEV strains are characterized as subtype, the European subtype shows a
European subtype. As noted, some other parallel evolution. All currently known strains
TBEV-EU strains have been identified and seem to originate from a single genetic clade.
isolated in South Korea. 13,16,17

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