Page 20 - TBE_Book_V2_2019

Chapter 1: A short history of TBE

lication strategies of alpha- and flaviviruses, from I. persulcatus, from rodents and patients
the family Flaviviridae was established as an serologically closely related to the strain Aina.
independent family that comprises the genus Gritsun et al. 25,54 were the first to genotype
Flavivirus with more than 70 species dividing strains of the Siberian subtype by gene E and
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into 10 serocomplexes. According to modern complete genome sequencing. Two strains –
classification, the family Flaviviridae comprises Vasilchenko (L40361) and Zausaev (AF527415)
the genera Flavivirus, Pestivirus, and Hepaci- – became prototype strains of 2 Siberian sub-
virus. TBEV belongs to the mammalian tick- type clusters (reflecting their geographic local-
borne flavivirus group and comprises 3 sub- ization).
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types: European, Far Eastern, and Siberian.
Sequencing a gene E fragment (160 bp length)
Two geographic and antigenic variants of TBEV of 8 and thereafter 29 strains isolated in differ-
(Eastern and Western) had been known for 40 ent geographic regions, carried out by Zlobin
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years. 1,41-44 Clarke divided 28 strains in 2 anti- et al. 55-57 enabled the identification of 3 major
gen variants by the gel precipitation test with genotypes (subtypes): (1) Far Eastern, (2)
cross-absorbed sera. She concluded that there Western, and (3) Ural-Siberian (Siberian). Ac-
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are 2 antigen subtypes: Eastern and Western cording to Ecker, TBEV consists of 3 subtypes
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(Central European). Chumakov et al. consid- corresponding to 3 major genotypes: Europe-
ered that Eastern and Western subtypes differ an, Far Eastern, and Siberian. However,
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within the species TBEV; they proposed a clas- Grard reinterpreted the data of the genetic
sification into ‘Persulcatus’ and ‘Ricinus’ anti- relationships among arthropod-borne viruses.
gen variants according to viral ecology. Voty- She suggested that TBEV should include 4 sub-
44,46
akov et al. argued that the infectious types: (1) Louping ill virus (Spanish, British,
agents of Eastern and Western TBE are differ- and Irish subtypes), (2) TBEV (European sub-
ent species according to differences in antigen type), (3) TBEV (Far Eastern and Siberian sub-
profiles, geography, clinical and pathological type), and (4) Turkish sheep encephalitis virus
features in animals and humans. and its subtype, Greek goat encephalitis virus.
Pletnev et al. 47,48 and Mandl et al. 49,50 decoded Beside the 3 described and accepted subtypes,
the complete genomes of Eastern (Sofjin) and 2 different strains – 178/79 and 886/84 – have
European (Neudoerfl) strains and thereby been described by Russian researchers. These
started a new phase of intraspecific TBEV clas- 2 strains have been shown not to be closely
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sification. The obtained data proved that the related to any of the 3 known subtypes.
genetic differences between the Western and Additional studies are needed to demonstrate
Eastern variants are significant with 16.8– whether these strains can be classified as new
16.9% of nucleotide substitutions and 6.9– TBEV subtypes. These results mean also that
7.2% of amino acid substitutions. Two Eastern further TBEV subtypes may be detected in
strains in contrast have 3- and 4-times lower future.
differences in nucleotide (4.6%) and amino
acid (1.8%) substitutions, respectively.

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Rubin and Chumakov published the first re- Acknowledgement: We are most grateful to
sults of the Siberian subtype. They demon- Jeremy Gray who helped improve the manu-
strated some peculiarities of the strain Aina script.
isolated in the Irkutsk region, USSR, from a

52,53
child with TBE. Pogodina et al. described a
group of strains isolated in Eastern Siberia Contact: olaf.kahl@berlin.de

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