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Chapter 3: Transmission / Natural cycle

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Red foxes (Vulpes vulpes) are known to be virus. The female tick is considered to play
reservoir-competent for TBEV. 90,91 Although I. only a minor role in virus transmission. Tick
hexagonus is a proven vector of TBEV, little is males, which either do not feed or feed for
known about the vector competence of the only a short time, might also be involved in
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fox tick I. canisuga. virus transmission. TBEV invades all tick
tissues, including the salivary glands and
In recent years, the detection of viral RNA in ovaries, thus it may be transmitted by ticks
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hosts has become possible. Tonteri et al. , in in the following ways: 1) via saliva, 2)
Finland, detected the European (TBEV-EU) and transovarially (vertically), and 3) sexually. 40,97–
Siberian (TBEV-Sib) subtypes in M. glareolus, 99
TBEV-Sib in the shrew Sorex araneus, and
TBEV-EU in Microtus agrestis. Achazi et TBEV transmission from vector ticks
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al. detected TBEV RNA in rodent brain tissue to hosts via saliva
in prevalences up to 20% in TBE non-risk as

well as risk areas in east-German Federal
Ticks are vectors and reservoirs of TBEV, and
States. Unfortunately, we do not know
they transmit the virus already when they
whether those rodents maintained living virus start feeding 43,100 with viral particles contained
nor their infectivity for feeding ticks. In the in the saliva, which the ticks release into the
Novosibirsk region of Siberia, where I. 40
persulcatus and I. pavlovskyi are the main host tissues during feeding.
TBEV vectors, the prevalence of TBEV viral
TBEV is present in the alveolar cells of the
RNA in 5 small mammal species was extremely
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high. It ranged from 35.3% for A. agrarius salivary glands of D. marginatus and H. inermis
organs to 82.2% for Myodes rutilus blood, with females in as few as 5 days after their feeding
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a mean value for all species and tissues of on viremic white mice. Also animal hosts are
important for the amplification of the virus
62.1%. All 3 virus subtypes were represented.
and are together with vector ticks the basis for
In addition to small mammal hosts, larger wild 101
the heteroxenous TBEV perpetuation.
and domestic animals frequently have high
antibody prevalences.
hey can be used as Viremic transmission from hosts to
sentinels for the occurrence of TBEV in a given feeding ticks
area.
Ticks become infected with TBEV while they

feed on a viremic host. 98,99,102 Nosek et al. 103,104
TBEV transmission proved that a viremia in a host lower than 10
1
mouse LD 50./0.03 ml was insufficient to cause
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Nuttall noted: “Reciprocal interactions of infection in ticks. In individual engorged I.
1 4
parasites transmitted by blood-sucking ricinus ticks, the virus titer was 10 −10 mouse
arthropod vectors have been studied primarily LD 50/0.03 ml. Viremic white mice served as
at the parasite-host and parasite-vector virus donors. 103,104 Grešíková and Nosek 105
interface. The third component of this parasite demonstrated the persistence of TBEV in H.
triangle, the vector-host interface, has been inermis (from larva to nymph) and then the
largely ignored.” transmission from H. inermis nymphs to white
mice. Viremia surpassing the threshold values
Every active tick stage can be infected with of infectivity for tick vectors was also found in
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TBEV, and approximately 0.1–1% of the ticks some juvenile and adult Myodes rufocanus, M.
– rarely more – in an endemic area carry the rutilus, and Micromys minutus. The viremia

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