Page 209 - TBE_Book_V2_2019

Chapter 11: General epidemiology of TBE

countries, the available seroprevalence rates Recently, data on the prevalence of antibodies
in different countries in the normal population and virus were tested in wild and domestic
range from 0% to 39%. However, the highest animals to identify species that might be used
of these values are usually found in special as surrogates for detection of endemic areas.
geographic conditions, for example 39% on
Finnish islands in the Baltic Sea. Usually the The role of particular mice and voles,
seroprevalence rates in European populations Apodemus flavicollis and Myodes glareolus,
range from 0% to 5% (Table 1). respectively, as primary vertebrate hosts for
the virus in the transmission cycle was
While other studies on the prevalence rates in demonstrated in a number of isolations of
high-risk populations resulted in similar rates, virus strains in TBE natural foci and through
some also indicated more extreme values experimental infections. 61–63 Also, Apodemus
under special conditions, e.g. >30% to 40% in sylvaticus seems to support the transmission
some groups of forest workers in Poland cycle as evidenced by high seroprevalence
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(Table 2). rates in Switzerland. In a recent study,
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Achazi et al. detected TBEV using molecular
These data showed that the risk of acquiring techniques in 6 rodent species in Germany:
TBE infection might be high, both in an Apodemus agrarius, Apodemus flavicollis,
exposed general population and in a high-risk Apodemus sylvaticus, Microtus arvalis,
population. However, many of these studies Microtus agrestis, and Myodes glareolus. The
were conducted before the introduction of seroprevalence rates in rodents of different
vaccines. Therefore, awareness of the disease areas ranged from 0% to 72% (Table 3).
among the general population in rural areas
was low and personal protection measures While the role of mice (Muridae) and voles
usually were not applied. This might be one (Cricetidae) for TBEV transmission seems
reason why in some areas the seroprevalence clear, the importance of Insectivora is still not
rates in the normal population might be in a finally clarified. Different studies show that
similar range as seen in highly exposed groups. hedgehogs (Erinaceidae) are highly infested
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with ticks. Kozuch et al. detected up to 50%

seroprevalence rates in hedgehogs in a study
Seroepidemiology in animals in Slovakia, and they could isolate a strain of
TBEV from the hedgehog. Even less clear is the
role of shrews (Soricidae). However, TBEV was
Humans are not natural hosts of the TBEV.
isolated from a brain of a common shrew,
Therefore, the seroprevalence rates in 66
humans usually give an incomplete picture of Sorex araneus. According to early studies,
TBEV epidemiology. During the past few the common mole (Talpa europaea) produces
decades, a number of studies have been high viremia and therefore may act as a
undertaken to study the seroprevalence rates maintenance host in the natural transmission
cycle. Systematic seroprevalence data on TBE
in different species of wild and domestic
animals. The seroprevalence rates of antibodies in insectivores are not available.
particular animals can document the presence
of a transmission cycle. These data may also In addition, seroprevalence studies in foxes
help with understanding the intensity of and correlations with human TBE are limited.
transmission in the natural cycle. In addition, One study on TBEV seroprevalence in foxes
they may document the role of particular from different areas in Germany found
animals in virus transmission and in the prevalence rates from 0% in Brandenburg to
maintenance of the TBE transmission cycle. 10% in the Odenwald and Taunus region (a

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