Page 67 - TBE_Book_V2_2019

Chapter 3

Transmission /

Natural cycle

Lidia Chitimia-Dobler, Ute Mackenstedt, Olaf Kahl
and Trevor N. Petney

Key Points

• The natural cycle of the TBE virus is dependent on vector ticks and their hosts.

• Enzootic cycles vary between different habitats and involve sympatric tick vector and host
species.
• There are differing transmission cycles in varying environments, from cold northern coniferous
forests to temperate central European forests.
• Within a natural transmission cycle there are complex differing transmission possibilities – tick
to tick (transovarial, sexual), host to tick (viremic), host to host and transstadial persistence.
• The complexity of natural transmission cycles is inadequately explored and poorly understood.

Introduction
Ticks play a critical role in the transmission of ing tick species not commonly in contact with
4,5
a wide variety of viral, bacterial, and humans. Thus, the transmission of tick-
protozoan pathogens to humans and borne pathogens often comprises a complex
1,2
animals. In the case of humans, infection is network of interactions involving several tick
accidental as these transmission cycles are and host species. Below, we provide back-
invariably enzootic with the natural hosts ground to the biology of ticks and how this can
most frequently being wild birds and influence, specifically, the eco-epidemiological
1
mammals. In order to be tangentially affected cycle of tick-borne encephalitis virus (TBEV).
by such cycles, humans must be bitten by a tick

species commonly found in habitats visited by
humans, as well as the tick’s usual hosts, as Structure and morphology
the dispersal of ticks not attached to hosts
3
covers only very short distances. In addition,
Ticks are a group of hematophagous
the tick has to accept humans as a suitable ectoparasites with about 900 living species.
6
host, meaning that the species involved They belong to the phylum Arthropoda, the
usually have a broad host spectrum.
class Arachnida, the superorder Acarina, and
the order Ixodida, and they are exclusively
Nevertheless, these tick species may only be
parasitic. The Ixodida contain 3 families: the
part of the transmission cycle, with eco- Ixodidae with 14 genera (hard ticks), the
epidemiologically significant sub-cycles involv-

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