Page 208 - TBE_Book_V2_2019

Chapter 11: General epidemiology of TBE

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indicating their ecological connection with all 1979 from a tick pool of Ixodes persulcatus.
elements of transmission chain. Despite the The single available isolate and genome
fact that these strains were isolated over 20 sequence show 10 to 16% difference to other
years ago, their circulation probably continues TBEV subtypes on nucleotide level and 3 to 6%
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in natural foci. Thus, 2 TBEV strains similar to difference on amino acid level.
the reference strain of the Baikalian subtype
were described recently in the territory of Chinese researchers reported on another new
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Transbaikalia from a taiga tick (in 1999) and 1 TBEV subtype. Two TBEV sequences were
strain from Myodes rutilus (in 2010). 58,59 Also, detected in two specimens of Marmota
in 2010, a report was published on a case of himalayana, collected in the Haixi prefecture
fatal meningoencephalitis in Mongolia caused at an altitude of 2,994m in the Qinghai-Tibet
by a TBEV isolate having a high degree of Plateau in China. So far, no virus isolates are
homology in the E gene fragment (98.5%) with reported. Only the sequence of the complete
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strains of the 886-84 group. The case was genome and of the viral polyprotein have
described in Bulganskiy aimak, bordering to been available. According to these data, the
the south with foci where TBEV group 886-84 virus differs in 16 to 18% on nucleotide level
strains had been isolated previously. The and on 6 to 8% on amino acid level from all
patient was hospitalized with meningo- other TBEV subtypes. According to a phylo-
encephalitis on the 11th day after a tick bite genetic analysis the putative new subtype
and then died that same day. The presence of diverged earlier from the Far-eastern subtype
TBEV RNA in macromyelon samples, in the than the Siberian subtype.
core and the meninx vasculosa, demonstrated
the multilevel localization of lesions and was
typical of the most severe forms of acute TBE
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that result in death or disability. Seroepidemiology in humans
The analysis of complete amino acid From the start of the use of antibody testing in
sequences of polyprotein from some strains this field, the prevalence rates of antibodies
confirmed that it is a “mixture” of sequences against TBEV (and other pathogens) were used
common for the 3 genotypes. Twenty-nine to estimate the burden of infection as well as
unique substitutions were detected that could the burden of disease in human populations.
probably be genotype-specific for group 886 Although these rates depend on a number of
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members. The studies of biological different factors (such as a person’s age,
properties demonstrated that group 886 profession, leisure activities, place of living,
strains have a wide spectrum of antigenic interest in nature/outdoor activities, degree of
properties, hemagglutination and neutralizing protection measures, knowledge about
activities, high virulence, and thermo- disease and transmission, and vaccination
tolerance. status, as well as presence of cross-reacting
viruses, assay technology used, etc.), the data
Other putative subtypes at least serve as a rough indication for the
presence or absence of TBE in an area.
Besides the now four accepted subtypes there
are two genetically distant groups of viruses, In determining TBE seroprevalence rates,
which show high genetic distance to all known studies in the normal population have to be
TBE virus strains. One virus was isolated only distinguished from studies and their results in
once. The prototype strain which is named highly exposed professionals such as
“strain 178-79” (EF469661) and was isolated in woodcutters, farmers, or hunters. In European

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