Page 19 - TBE_Book_V2_2019

Chapter 1: A short history of TBE

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Chumakov & Naidenova (cited after ) found workers made a number of further relevant
the hard tick I. ricinus, a close relative of I. contributions to this topic. 31-33 They found (i)
persulcatus, to be a vector of a milder form of that TBEV is transported in Langerhans’ cells in
TBE in some European areas of the former infected hosts, (ii) that non-viremic transmis-
USSR. This was later confirmed by various Eu- sion also occurs in immune hosts, and (iii) that
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ropean researchers. Rampas & Gallia from this kind of transmission happens in small, but
Czechoslovakia were the first outside the for- not in larger mammals. The most commonly
mer USSR to isolate TBEV from field-collected used term now is ‘co-feeding transmission’,
ticks. although non-viremic transmission might tech-
nically be the better term.
An alternative alimentary route of human TBE
infection became apparent in the European
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part of the former USSR from 1947 to 1951.
Groups of people contracted TBE after con- The detection of different TBEV
suming unpasteurized goat milk or goat milk subtypes
products (e.g., cheese) from viremic goats.
Similar alimentary TBE epidemics occurred Based on general viral properties such as viral
also in other TBE endemic countries, e.g., in morphology, physical and chemical properties,
Rožňava (south-eastern Slovakia) with more virion structure, arthropod carriers, and sero-
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than 600 cases in 1951 and in Niesky (former logical cross-reactions, the genus Flavivirus
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German Democratic Republic) in 1961. including TBEV was considered to be part of
the family Togaviridae. This term was first
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Field work on TBEV decreased in several Euro- offered by Lwoff and Tournier (1966).
pean countries in the 1970s and 1980s. TBEV
ecology seemed to be well understood. The The family Togaviridae consisted of the genera
main interest of researchers focused more on Alphavirus (former arbovirus group A), Fla-
the molecular biology of TBEV and also on the vivirus (former arbovirus group B) with Den-
newly discovered Borrelia burgdorferi, the gue virus, type 1, and some other viruses. 35,36
causative agent of human Lyme borreliosis. 37
Interestingly, this coincided with the first Eu- De Madrid and Porterfield divided the genus
ropean TBE vaccine becoming available in Flavivirus into 7 subgroups according to
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1976, and the TBE problem seemed to be plaque reduction neutral-ization test (PRNT).
solved. The first subgroup includes tick- borne viruses
such as TBEV, Omsk hemorrhagic fever virus,
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Jones et al. made the significant finding in Louping ill virus, Langat virus, Negishi virus,
the laboratory that guinea pigs can infect and Kyasanur forest disease virus. Along with
feeding Rhipicephalus appendiculatus with the above-mentioned viruses, the TBEV com-
Thogoto virus, another tick-borne virus, with- plex included Alma Arasan, Apoi, Royal-Farm,
out showing an apparent viremia. Kadam, Powassan viruses, and according to
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Gaidamovich and Loginova also Gadgets
Encouraged by this finding, Alekseev & Chu- Gully, Saumarez Reef, Karshi, and Tyuleniy
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nikhin and Labuda et al. demonstrated viruses.
non-viremic transmission of TBEV from small
mammals (infected through tick bite) to unin- These viruses share some antigenic similarity
fected feeding ticks. This was a major step but have different geographic distributions,
forward in our understanding of the field ecol- associations with different ticks and verte-
ogy of the virus, and reactivated interest in brate hosts, and a different pathogenic poten-
TBEV ecology. Milan Labuda and various co- tial for humans. Due to a difference in the rep-

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