Page 273 - TBE_Book_V2_2019

Chapter 12b

TBE in Denmark

Anders Fomsgaard

History and Current Situation

Since the 1950s tick-borne encephalitis (TBE) A forest worker was infected in his backyard in
has been known to be endemic in Denmark Tokkekøb. The location is a small, open grass
but only on the island of Bornholm. Bornholm field bordering a lake and with a deer path
is situated east of mainland Denmark, south of (Photograph). The patient had not been
Sweden (Figure 3) and has a different fauna traveling. He described a similar case of
and flora from the rest of Denmark. Bornholm encephalitis in 2008, when a man working in
has about 45,000 inhabitants, but about the forest kindergarten just 500 m away got
500,000 tourists visit the island every year. tick bites at the same spot. Both subjects had
Freundt carried out a sero-survey during 1958 a typical biphasic disease and TBE was diag-
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- 1962 and found TBE antibodies in 1.4% of nosed. Both experienced persistent neuro-
blood donors and 30% of woodworkers on logical sequelae, paralysis of one arm (both
Bornholm but no antibodies in subjects living patients) and neuropsychiatric complications
in mainland Denmark. In 1963, Freundt found (one patient). TBEV European (Western) sub-
that 8 of 12 patients admitted to the hospital type (TBEV-E) was identified in 2009 in I.
with acute meningoencephalitis of unknown ricinus tick adults and nymphs from the
etiology during 1951–1960 had antibodies to location identified by both patients (the
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2
tick-borne encephalitis (TBEV). In 2000 TBE ‘smoking gun principle’).
was re-discovered on Bornholm, where a
retrospective study covering the period 1994– In July and Sept. 2011 TBEV-Eu was again
2002 (7 years) identified 14 TBE cases; 2 cases identified (endemic) in adults and nymphs at
were tourists and 12 were inhabitants of Tokkekøb, and TBEV isolated (isolates T2 and
Bornholm, giving an incidence of 3.81 per T3). The virus sequence grouped with isolates
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100,000 inhabitants. At least 5 patients from Sweden-Norway, whereas one Bornholm
(37.7%) got permanent sequelae. In addition, TBEV from 2012 grouped into a different
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32 forest workers on Bornholm were tested in subclade from South and Central Bohemia. A
2000, and 20% had IgG antibodies but never recent (2018) sequenced TBEV isolate from
symptoms. This is similar to the finding of Bornholm (lake Rubinsøen) grouped with
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Freundt in 1960. It was concluded that the TBEV from Switzerland and Finland. Whereas
data did not provide evidence of an increase some TBEV microfoci may contain TBEV
in incidence of TBE. Ticks (Ixodes ricinus) from unchanged for decades (Finland), other foci in
Bornholm were investigated for TBEV in 2000 Denmark may merely provide permissive
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and 2% were found to be infected. Since 2001 conditions for random and repeated TBEV
an average of 2.5 (range 1–8) TBE cases per introductions from various geographical
year have been reported in Bornholm (Figure locations. TBEV was not identified in 58 tick
1). In 2009 we succeeded in identifying a TBEV pools collected 2010–2011 in North Zealand,
microfocus in a small forested area, Tokkekøb Fuen, and Jutland by flagging or from roe
Hegn on Zealand just north of Copenhagen, deer. In addition, 78 patients in North Zealand
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which had a severe TBE case reported. with ‘summer flu’ after tick bites (July–Sept.

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