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Chapter 2a

Virology

Daniel Růžek, Kentaro Yoshii, Marshall E. Bloom

and Ernest A. Gould

Key Points

• TBEV is the most medically important member of the tick-borne serocomplex group
within the genus Flavivirus, family Flaviviridae.

• Three antigenic subtypes of TBEV correspond to the 3 recognized genotypes: European
(TBEV-EU), also known as Western, Far Eastern (TBEV-FE), and Siberian (TBEV-SIB).
Additional 2 genotypes have been identified in the Irkutsk region of Russia, currently named
TBE virus Baikalian subtype (TBEV-BKL) and TBE virus Himalaya subtype (Himalayan and “178-
79” group; TBEV-HIM).
• TBEV virions are small enveloped spherical particles about 50 nm in diameter.

• The TBEV genome consists of a single-stranded positive sense RNA molecule.
• The genome encodes one open reading frame (ORF), which is flanked by untranslated
(non-coding) regions (UTRs).
• The 5′-UTR end has a methylated nucleotide cap for canonical cellular translation. The 3′-UTR
is not polyadenylated and is characterized by extensive length and sequence heterogeneity.
• The ORF encodes one large polyprotein, which is co- and post-translationally cleaved into 3
structural proteins (C, prM, and E) and 7 non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A,
NS4B, and NS5).
• TBEV replicates in the cytoplasm of the host cell in close association with virus-induced
intracellular membrane structures. Virus assembly occurs in the endoplasmic reticulum.
The immature virions are transported to the Golgi complex, and mature virions pass through
the host secretory pathway and are finally released from the host cell by fusion of the transport
vesicle membrane with the plasma membrane.

Virus classification

Tick-borne encephalitis virus (TBEV) is the The genus Flavivirus comprises over 70 virus
most medically important member of the species, many of which are important human
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tick-borne serocomplex group within the pathogens. Besides TBEV, these include
genus Flavivirus, family Flaviviridae (from the mosquito-borne viruses such as dengue
Latin flavus – ‘yellow’, referring to the viruses, Japanese encephalitis virus, yellow
prototype virus, yellow fever virus). fever virus, Zika virus, and many others.
Virtually the entire human population lives

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