Page 355 - TBE_Book_V2_2019

Chapter 12b

TBE in Norway

Katrine M. Paulsen, Rose Vikse, Arnulf Soleng,
Kristin S. Edgar, Susanne Dudman, Berit Sofie Wiklund

and Åshild K. Andreassen

History and Current Situation

Ixodes ricinus ticks are mainly distributed and it is known for high temperatures during
along the Norwegian coastline from Østfold spring and summer. In addition, TBE
County in the southeast up approximately to antibodies in dogs and tick-borne encephalitis
1–5
66°N in Nordland County. The density of virus (TBEV) in ticks have previously been
ticks varies between locations, even when detected in the same area. 6–9
separated by short distances. Locations with a
high density of ticks are found all across the Since the first human TBE case reported in
major distributional range. The abundance of 1997, there have been a total of 143 cases
ticks declines rapidly with both increasing reported in Norway (data per January 2018).
distance from the coast and higher altitude Of these, 117 cases are autochthonous
(personal observation). A multi-source analysis infections, and 26 cases have been infected
by Jore et al. (2011) suggests that tick abroad or have an unknown infection history.
populations in Norway have undergone recent The number of cases has a yearly variation
23
latitudinal and altitudinal range shifts. between 1 and 16 cases (Table 1 and Figure 1).
Jenkins et al. (2012) found few ticks attached Preliminary data for 2018 show an increase in
to dogs and cats in the region north of 66°N, the number of cases, especially in the Vestfold
while Hvidsten et al. (2014) confirmed these and Telemark counties (personal communi-
findings and stated that further studies are cation Yngvar Tveten, Telemark Hospital). The
needed in order to clarify if tick populations age distribution of the TBE patients is in
4,5
are established north of the Arctic Circle. accordance with other European studies with
10,11
According to Soleng et al., ticks were higher case rates for those above 30 years
abundant at locations from 64.5 to 65.3°N, but (Table 2 and Figure 2). According to MSIS, the
few ticks were found at locations close to 66° reported cases in Norway represent the
N. At several locations from 66.3°N up to 67.6° counties of Vest-Agder, Aust-Agder, Vestfold,
N, no ticks were found by flagging and Telemark, and Buskerud, all located in the
3
dragging. southern part of the country (Figure 3). Cases
have been reported neither from the western
In Norway, tick-borne encephalitis (TBE) has or northern coastal areas, nor from the area
been a mandatory notifiable disease to the east of the Oslofjord, even though outdoor
Norwegian Surveillance System for Communi- recreation activities are common in the whole
cable Diseases (MSIS) since 1975. The first country.
reported case of TBE occurred in 1997 at
6 Recent studies in I. ricinus have detected TBEV
Tromøy in Aust-Agder County. This is a region
with holiday cabins and outdoor recreation in nymphs from the southern and eastern part
areas for both local inhabitants and tourists, of the country with a prevalence ranging from

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