Page 356 - TBE_Book_V2_2019

Chapter 12b: TBE in Norway

0.14% to 1.22%. 9,12 TBEV in nymphs and adults This is higher than in a previous study by
has recently been detected in northwestern Traavik (1973), where a seroprevalence of
and northern Norway up to approximately 66° 17.7% was detected in bovine sera in
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N, with a prevalence variation from 0% to western Norway.
3.0% in nymphs and 0% to 9.0% in adults. 3,13
Further, two seroprevalence studies in
Only one pool of ten nymphs collected from humans from presumed non-endemic areas
southern Norway has so far been whole have been published. 12,18 Larsen et al.
genome sequenced and phylogenetically detected TBE immunoglobulin G (IgG)
characterized. The sequence, strain Mandal antibodies among 0.65% of blood donors in
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2009, was found to belong to the Østfold County in southeastern Norway.
Scandinavian group of the European TBEV The second study in 1,213 blood donors was
subtype. Interestingly, strain Mandal 2009 performed in Sogn og Fjordane County,
revealed a shorter form of the TBEV genome, located in western Norway. TBE IgG
similar to the highly virulent Hypr strain, antibodies were detected in five (0.4%) of
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within the 3’ non-coding region. the samples. However, these were all
interpreted as false-positives owing to
In addition to tick studies, seroprevalence previous flavivirus vaccination causing
studies have detected TBE antibodies in antibody–positive status in four individuals
specimens from cervids (deer) collected in and a negative result in the neutralization
Farsund (Vest-Agder County) and Molde test for the fifth person. 18
(Møre og Romsdal County). In Farsund,
located on the southern coast of Norway, 41% Historically, the first suggested TBEV isolate
(22 of 54 animals) were found to be TBE- from Norway was collected in I. ricinus from
positive in contrast to Molde, situated mid- Sogn og Fjordane County in June 1976 as
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west, with 1.6% (1 of 64 animals). The same described by Traavik and coworkers. Five
study detected antibodies to Louping ill virus virus strains with close serological
(LIV), a closely related flavivirus, in 14.8% (8 of relationship to the TBEV complex were
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54) of the analyzed cervid sera from Farsund. detected in this study. In 1971, Traavik
LIV has not previously been detected in ticks detected a seroprevalence of 19.6% from
in Norway. Recently, 6,850 nymphs and 765 the same area. However, these results were
adult ticks from eastern, western, and not confirmed by neutralization test and
northern Norway were analyzed for LIV using thus may be explained by cross-reactions to
an in-house real-time polymerase chain LIV, vaccine-related flaviviruses, or
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reaction (PCR) assay (designed by Torstein nonspecific binding in the test.
Tengs). No positive ticks were found
(unpublished data from the Norwegian The results from both prevalence studies in
Institute of Public Health). ticks and seroprevalence studies in humans
and wild animals indicate that TBEV might
There is limited knowledge on TBEV in be widespread in Norway, and not limited
domestic animals in Norway. A recent study to the southern region. Further studies on
reported TBEV RNA in unpasteurized cow tick distribution and prevalence of TBEV in
milk from three farms located in southern ticks, humans, domestic animals, and wild
and northern Norway in 5.4% of the tested animals in Norway are currently ongoing.
animals. Seropositive animals were only
detected at one farm in southern Norway, in
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88.2% of the tested animals.

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