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Chapter 2a: Virology
Figure 4
Genome organization of TBEV and processing pathways of the polyprotein. A schematic representation of the
TBEV genome with the 5′ and 3′ non-translated regions (NTRs) is shown in the top; the translation products are
given below (kindly provided by Martin Palus, with permission).
The geographical distribution and clinical properties, the European TBEV strains are
significance of these newly identified geno- more closely related to LIV than to TBEV-FE
types remains to be determined. However, and TBEV-Sib strains. 14,15
some studies indicate that 0.6-6% of TBEV
strains circulating in Eastern Siberia might All TBFVs are thought to have shared a
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belong to these new genotypes. Another common ancestor, which diverged from
new potential TBEV subtype (Himalayan – mosquito-borne flaviviruses in Africa less than
16–18
TBEV-Him) was identified recently in wild 5000 years ago. However, some studies
rodents in Qinghai-Tibet Plateau in China. 118 suggest that this split might have occurred as
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long as 50,000 years ago. The descendant
Comparison of the complete coding sequences TBFV species evolved and spread through Asia
of all recognized TBFV species led to a new and then more recently westwards through
taxonomic proposal, viz. the assignment of Europe as they adapted to different host and
TBEV and LIV to a single species (TBEV) tick species. 16–18 In comparison with mosquito-
encompassing 4 viral types; i.e., Western TBEV borne flaviviruses, TBFVs evolved nearly twice
(TBEV-EU); Eastern TBEV (TBEV-Sib and TBEV- as slowly, primarily due to the long life-cycle of
FE); Turkish sheep TBEV, including Greek goat the Ixodes tick vector. 16,20,21 Overall, it was
encephalitis virus subtype; and Louping ill concluded that there is a direct correlation
TBEV, the latter having Spanish, British, and between genetic and geographic distance of
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Irish subtypes. This classification was individual TBFV species 16,22 and, furthermore,
supported by the fact that, based on antigenic that the evolution and dispersal of these
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