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Chapter 11: General epidemiology of TBE

The sequencing of the E gene fragment of 6 including Zausaev strain (AF527415) was
samples (Figure 3) shows that these TBEV characterized by H234/ A431, whereas strains
variants corresponded to TBEV-FE, and a of the second lineage including Vasilchenko
number of observed nucleotide substitutions strain (AF069066) revealed Q234/ T431. 52,53
(and amino acid substitutions in the Later, the “Baltic lineage” 50,54–56 and
57
corresponding E protein fragment) were not “European topovariant” of TBEV-Sib were
previously described. Thus, the appearance of described. Also, the heterogenicity of TBEV-Sib
new variants of highly pathogenic, atypical was demonstrated by molecular hybridization
TBEV can be evidence of the continuing of nucleic acids with 2 subgenotype-specific
evolution of this virus group. probes (designated as 3a and 3b)
differentiating lineages/ subgenotypes
In 2004, the TBEV Glubinnoe/2004 strain was “Vasilchenko” and “Zausaev” of Siberian
isolated from the brain of a deceased patient subtype (Figure 4). The Zausaev and
10
in the Primorsky region of far eastern Russia. Vasilchenko lineages were found in various
The sequencing of its genome demonstrated regions of Eurasia at different ratios, and
that this TBEV variant corresponds to TBEV-FE, moreover, some TBEV strains of Siberian
but has 53 or 57 substitutions in polyprotein subtype could not be attributed to any of
amino acid sequence compared with Far- these lineages.
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Eastern strains 205 (DQ989336) or Sofjin-HO
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(AB062064), respectively, and 14 of these Baikalian subtype
substitutions are unique and have not been
41
described previously. Researchers also found In addition to the 3 primary and accepted
that Glubinnoe/2004 has a high level of TBEV subtypes, 2 groups of TBEV strains
production of infectious viral particles during supposed to be new TBEV subtypes were
the early stages of infection in cell cultures as described. At this time, the members of now
compared with other Far-Eastern 205 accepted fourth prototype strain 886-84
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strains. (EF469662, KJ633033) subtype have been
found only in the Republic of Buryatia, in the
Siberian subtype Irkutsk and Chita regions of Eastern Siberia
and in northern Mongolia (Figure 5). 10,21,51 This
The TBEV-SIB subtype is the most common subtype is also now named “Baikalian
TBEV and has been found almost everywhere subtype” and about 20 TBEV strains have been
in TBEV habitat areas. Thus, it has been identified and genetically characterized. 10,49,51
detected in most parts of Russia, including the These strains (called the “886-84 group”) form
central and northwestern regions, Ural an independent cluster on the TBEV
Mountains, Western and Eastern Siberia, the dendrogram (see Chapter 2) and have no close
Far East, etc., 10,12,28,42–44 as well as in homology with any strains of the 3 original
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Mongolia, Kazakhstan and Kyrgyzstan, 46–49 subtypes. Within the group, high homology
12,50
Finland and the Baltic countries, (more than 98%) of nucleotide sequences was
49
Ukraine, 28,49 and the Balkan peninsula. observed while the genetic differences with
other subtypes were shown to be greater than
TBEV-SIB is believed to be the most genetically 12%.
51
heterogeneous, with a nucleotide substitution
51
level about 5.4% within the subtype. At first, TBEV strains of the Baikalian subtype were
based on the analysis of E protein sequences isolated from ticks and small mammals
at amino acid positions 234 and 431, two collected in the Irkutsk region, Buryat
genetic lineages were defined: one lineage Republic, and Transbaikalia in 1984-1990

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