Page 349 - TBE_Book_V2_2019

Chapter 12b

TBE in the Netherlands

Tabitha Elina Hoornweg and
Johannes Hermanus Jozef Reimerink

History and Current Situation
Until 2015, tick-borne encephalitis virus (TBEV) TBEV strains. Based on the near complete
was presumed not to be endemic in the genome, the ‘Salland’ strain diverges from
1,2
Netherlands. Consequently, the number of currently known TBEV-Eu strains by 9% on
diagnostic requests for detection of tick-borne nucleotide and 2% on amino acid level,
encephalitis (TBE) infection has been low. respectively.
Between 2006 and 2015, the laboratory of the
Netherlands Centre of Infectious Disease In 2016, soon after the National Institute for
Control, 1 of the 2 laboratories that performed Public Health and the Environment raised
TBEV diagnostics in the Netherlands at the national awareness about the presence of
time, received an average of 20 (range 12–27) TBEV in the Netherlands, the first 2
5,6
requests for TBE diagnostics per year. In the autochthonous TBE cases were reported.
same period, TBE was diagnosed in 7 Dutch Both patients were positive for TBEV by ELISA
patients. All of these cases were considered to and virus neutralization test. The first patient
be travel-related. Indeed, 6 out of 7 patients most likely acquired TBEV when hiking at
2,5
reported that they had recently travelled to national park ‘Utrechtse Heuvelrug’ located
TBEV-endemic countries such as Austria (4), in the center of the Netherlands (Figure 3). A
Germany (1), and Sweden (1). tick collected from this patient was PCR-
positive for TBEV. Interestingly, the virus strain
In 2015, however, six out of 297 (2%) roe deer from this tick was genetically similar to known
sera, collected in 2010, were found Western European TBEV strains, and differed
serologically positive for TBEV-infection. 2,3 5 considerably from the Salland strain (9% on
out of 6 sera centered at the national park nucleotide level, 2% on amino acid level). The
‘Sallandse heuvelrug’ in the province of second patient lived near the national park
Overijssel, in the east of the Netherlands. The Sallandse heuvelrug and frequently visited this
2
other TBEV-positive roe deer serum was park.
collected in the south of the Netherlands, in
the province of Noord-Brabant. Based on In 2017, a new serosurveillance study was
these findings, I. ricinus ticks were collected at conducted in roe deer, reporting that the
the ‘Sallandse heuvelrug’ in 2015. From the number of TBEV foci in the Netherlands likely
approximately 1,460 ticks collected in 2015, increased during the period of 2010-20177.
one pool of nymphs (0.09%) and one pool of Next to the known TBEV focus at the
female adult ticks (0.33%) were PCR-positive ‘Sallandse heuvelrug’, nine additional potential
3,4
for TBEV. Sequencing of the viral genome TBEV foci were identified, mainly located near
revealed that the virus groups with the the borders with Germany and Belgium
European (Western) subtype, but is genetically (Figure 4). Moreover, three additional
distinct from all known Western European autochthonous human cases were reported in
2017 and 2018. Again, one patient lived close

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