Page 156 - TBE_Book_V2_2019

Chapter 8: TBE in animals

unpasteurized milk. Consumption of such tick population as the small mammals are for
products may have led to an alimentary larvae and nymphs (see below). It is common
infection of a group of individuals who to find hundreds of ticks per individual and,
became infected through the same batch of consequently, the odds of roe deer becoming
contaminated food, resulting in clusters of infected in TBE-endemic areas are rather
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human cases. Such clusters of cases have high. Therefore, they can be a useful tool to
2
recently been reviewed and were thought to identify endemic areas as could be seen in the
be restricted to nations in Eastern Europe. Netherlands, where TBE was regarded as an
However, alimentary TBEV infection with imported disease until 2016. Serologic
clinical TBE occurred recently in Germany as a screening there showed TBEV-neutralizing
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result of consumption of fresh raw goat milk . antibodies with a seroprevalence of 2% in roe
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As there is a growing trend towards consump- deer. However, clinical or pathological signs
tion of natural food products in the industrial- that raise suspicions of an overt TBEV
ized nations of Western Europe, such infection have never been described for roe
scenarios may be witnessed more frequently deer. Seroconversion after infection seems to
in the future. One study in an endemic region be the rule, and this fact has been widely used
in Poland found TBEV in milk from sheep to estimate TBE prevalence in certain areas. As
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(22.2%), goats (14.8%), and cows (11.1%). In roe deer are territorial animals, many
Norway, a study found TBEV RNA in 5,4% of researchers claim that this serological data
tested raw milk samples. Positive blood serum could be very useful in finding and describing
samples only occurred in one municipality, possible TBE-endemic areas, in particular in
where 88.2% of tested cows had specific low-endemic areas or regions in which TBE
antibodies. Remarkably, none of the cows cases in humans are reported only
with a positive milk sample had detectable sporadically. 50-57 The discrepancy of often
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antibodies and vice versa. Domestic double-digit percentages of seroprevalence in
ruminants do develop an antibody response, roe deer and no, or almost no, human cases is
which in the case of goats and sheep is puzzling, and needs to be investigated further.
measurable for at least 28 months. 23,27 As TBEV is known to be circulating in such
Exposure to TBEV seems not to result areas, an understanding of why only few or no
uniformly in seroconversion of the entire flock human cases occur could be key to developing
of animals. 45,46 Whether this indicates that not strategies aimed at reducing TBE incidence in
all animals of the same herd were exposed high-endemic areas (as defined by the number
and infected or that some animals did not of human cases). Likewise, the wild boar (Sus
mount an immune response is not known. scrofa) is present all over Europe and is
Also, the extent of antibody response seems commonly infested with ticks. There are no
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to vary between the species. records of a possible TBE-like disease in wild
boar and only 2 studies investigated the

seroprevalence against TBEV in wild boar.
Game animals Nevertheless, these studies demonstrated a
surprisingly high percentage of animals with
(wild boar, cervids, foxes) antibodies against TBEV in areas with no
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notified human TBE cases. A sero-survey of
Roe deer (Capreolus capreolus) are the most wild boar in Belgium revealed the presence of
abundant cervids in Germany, sharing their TBEV, with 2.9% of the 238 wild boar
habitat with ticks everywhere. They are well investigated having specific neutralizing
known as hosts for nymphs and adult ticks and antibodies against TBEV. As Belgium is
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thus are as important to maintenance of the considered to be traditionally free of

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