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Chapter 11: General epidemiology of TBE

In contrast, the Siberian subtype shows a Republic of Bashkortostan, Ural Mountains,
more consecutive genetic evolution. Only Siberia, and the European part of Russia. 10,28–32
recently, a TBEV strain from The Netherlands In some territories, TBEV-FE has been more
was shown to have a distant genomic prevalent in urban and suburban areas. 33,34
relationship to all other TBEV-EU strains. Also, TBEV-FE can cause different forms of
35,36
While TBEV-EU has also been identified and disease, from subclinical to acute.
isolated outside Europe, the phylogenetic
connection between European strains and the Within this subtype at least 4 separate groups
Siberian and Korean strains is as yet unclear. (lineages) of TBEV have been described (Figure
3). The first group consists of TBEV strains
A number of phenotypic characterizations similar to Sofjin strain, which was isolated in
have demonstrated TBEV strains of differing the Khabarovsk region of Russia in 1937 from
1
pathogenicity, which are circulating in nature. a patient’s brain (Zil’ber, 1939) and includes
The TBEV strain MucAr HB171/11 shows low strains from far eastern Russia, Japan, China,
neuropathogenicity and neuro-invasiveness in Latvia, and the European part of Russia. 26,27
9
a mouse model. A Czech strain, ts263, is a The group of strains similar to the Oshima
temperature-sensitive strain that does not strains isolated in Japan on Hokkaido Island
grow at 40°C and also exhibits non-neuro- forms a separate cluster on phylogenetic
19
invasiveness. dendrograms that is significantly different
from the Sofjin strains group 20–22 and includes
In addition, TBEV-EU is mainly associated with TBEV strains from Japan, China, and the
the biphasic form of TBE. So far, no chronic Crimean peninsula. 26,27 The third group
forms of disease caused by TBEV-EU have consists of the Chinese Senzhang strain, which
24
been reported. The clinical picture of infection was isolated from a patient’s brain in 1953;
ranges from subclinical to febrile disease to the MGJ-01 strain, which was obtained from a
CNS symptoms with severe and persisting patient’s blood serum and used in China for
neurological sequelae in up to 10% of human the production of vaccines and immuno-
cases. The fatality rate of infections with biologic drugs; and other strains from far
37
TBEV-EU ranges from 1% to 2%. Acute fatal eastern Russia. In addition, the fourth group
cases have been rare since a fast-acting formed by TBEV-FE strains from Japan
treatment of brain edema was introduced. (Kam586/97(AB237185), Kam588/97(AB237186))
27
Disease sequelae and fatal cases are mainly has been described. The time of divergence
seen in elderly patients. The fatalities often among different TBEV- FE clusters within the
result from super-infections (e.g. pneumonia) Far-Eastern subtype was estimated at
relating to the neurological sequelae (e.g. approximately 470 to 650 years ago (Figure 3).
paralysis of breathing muscles); therefore
these conditions must be named as indirect Also, within TBEV-EU some unique virus
causes of fatalities due to TBE. variants have been described. In 1999, in the
southeast of the Novosibirsk region of
Far-Eastern subtype Western Siberia, Russia, cases of hemorrhagic
forms of TBE with fatal outcomes were
The TBEV-FE viral subtype can be preferably reported. Previously, infections resulting in a
38
found in the territory of the far-eastern part of hemorrhagic disease had not been described
Eurasia. 20–27 However, this subtype was for TBEV, although other tick-borne flavi-
detected in other regions of Eurasia, including viruses such as Omsk hemorrhagic fever virus
the Baltic countries, the Crimean Peninsula, and Kyasanur forest disease virus may cause
the Republic of Moldova, the Republic of blood-clotting (see section 6 below).
Belarus, and the territories of Komi Republic,

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