{"id":28360,"date":"2026-06-06T13:01:36","date_gmt":"2026-06-06T05:01:36","guid":{"rendered":"https:\/\/tbenews.com\/tbe\/?p=28360"},"modified":"2026-06-23T17:34:04","modified_gmt":"2026-06-23T09:34:04","slug":"13-24-9","status":"publish","type":"post","link":"https:\/\/tbenews.com\/tbe\/13-24-9\/","title":{"rendered":"Norway"},"content":{"rendered":"\n
<\/a><\/span>
\n

TBE in Norway<\/strong><\/h1>\n<\/div>\n\n\n\n

\u00c5shild K. Andreassen, Andrea P. Cotes-Perdomo, Arnulf Soleng,
Urusha Maharjan, Heidi H. Lindstedt, Kristian Alfsnes, and Rikard Rykkvin<\/strong><\/p>\n\n\n\n

(last edited in June 2026, update for 2024: 78 reported cases; update for 2025: 97 reported cases)<\/em><\/em><\/p>\n\n\n\n

History and current situation<\/h3>\n\n\n\n

In Norway, tick-borne encephalitis (TBE) has been a mandatory notifiable disease since 1975 (Norwegian Surveillance System for Communicable Diseases, MSIS).1<\/sup><\/a> According to ECDC’s classification, coastal areas in southern Norway (counties of Agder, Vestfold and Telemark) are endemic for TBE. Further, the counties of \u00d8stfold, Akershus, and Buskerud, and western and northern Norway to Br\u00f8nn\u00f8y municipality are imperiled.2-12<\/sup><\/a>

The first reported case of TBE occurred in 1997 at Trom\u00f8y in Agder County.13<\/sup><\/a> This is a region with holiday cabins and outdoor recreation areas for both local inhabitants and tourists, and it is known for high temperatures during spring and summer. In addition, TBE antibodies in dogs and tick-borne encephalitis virus (TBEV) in ticks have been detected in this area.10,12-15<\/sup><\/a>

A total number of TBE cases have been reported to MSIS as of February 2025 (Fig. 1). Of these, the majority are autochthonous infections, while the remainder were infected abroad or have an unknown infection history. The number of cases varies annually between 1 and 97 (Table 1 and Fig. 1). Data from 2018 to 2025 show an increase in the number of reported cases, especially in the counties of Vestfold and Telemark (Fig. 5). In 2023, the first case from Vestland County was reported to MSIS. The TBE patients\u2019 age distribution is in accordance with other European studies, with a higher infection rate among those older than 30 years (Table 2 and Fig. 2).16\u201317<\/sup> According to MSIS, the reported cases in Norway are represented mainly by the counties of Agder, Vestfold and Telemark, and Viken, all located in the southern part of the country (Fig. 3). No cases are reported from the northern coastal areas, although a few cases are reported from the western areas and the area east of the Oslofjord, despite outdoor recreational activities being common throughout the country.<\/p>\n\n\n\n

Ticks and TBEV in Norway<\/h3>\n\n\n\n

The castor bean tick (Ixodes ricinus<\/em>) is the most common tick species in Europe,18<\/sup><\/a> and considered to be the major vector of the European TBE-virus.19-20<\/sup><\/a> The geographical distribution of I. ricinus<\/em> in Norway has been investigated in several studies.2-4,10,21-25<\/sup><\/a> Both Tambs-Lyche (1943) and Mehl (1983) found I. ricinus<\/em> to be mainly distributed in the coastal areas of Norway, from the southeastern border to Sweden, along the southern and western coastline, up to Nordland County at ~65.1\u00b0N.2,3,21-25<\/sup><\/a> The density of ticks varies between locations, even when separated by short distances. This is probably caused by differences in microclimatic conditions, vegetation, and density of vertebrate hosts. However, locations with a high density of ticks are found all over the major distributional range. The density of ticks declines rapidly with both increasing distance from the coast and increasing altitude. In a multi-source study, Jore et al. (2011) suggested that tick populations in Norway had undergone recent shifts in latitudinal and altitudinal range.7<\/sup><\/a> This result is, however, disputed in recent studies.4,5<\/sup><\/a>

\n\nAlthough ticks are reported far outside (i.e. northeast) of the hitherto established distribution limit of I. ricinus<\/em> in Norway, the vast majority of these are engorged females.24-26<\/sup><\/a>

\n\nMigratory birds may deposit engorged larvae or nymphs in areas where temperatures permit development to the next stage but not completion of the life cycle. Thus, such records do not constitute evidence for established and sustainable tick populations as this requires the presence of all the active stages (larvae, nymphs, and adults) in a locality for at least two consecutive seasons.27,28<\/sup><\/a> Using flagging and dragging, Soleng et al. (2018) found tick larvae, nymphs and adults to be abundant at 64.5 and 65.1\u00b0N. Only a few tick nymphs and adults, and no larvae, were found at locations close to 66\u00b0N.<\/p>\n\n\n\n

At several locations from 66.3\u00b0N up to 67.5\u00b0N no ticks were found.3 In a recent study by Hvidsten et al. (2020), the occurrence of ticks in northern Norway was examined by dragging in 109 separate locations between the latitudes of 64\u00b0N and 70\u00b0N. The northernmost location with a permanent I. ricinus population was at 66.2\u00b0N on the Island of D\u00f8nna (Fig. 4).5,6 It is noteworthy that the taiga tick (Ixodes persulcatus) and the meadow tick (Dermacentor reticulatus) were not detected in a large screening of ticks collected in the southern part of Norway in 2016.29

Studies of I. ricinus in Norway have detected TBEV in nymphs with a prevalence ranging from 0% to 1.1%. In adult ticks collected from the same areas, the prevalence ranges from 0% to 20.6%. TBEV positive ticks have been found in sampling areas along the Norwegian coastline from the east of \u00d8stfold County to Br\u00f8nn\u00f8y in Nordland County.12 The highest estimated TBEV prevalence in adult ticks has been found in the counties of Rogaland and Vestfold and Telemark. In nymphs, the highest prevalence has been found in Vestfold, Telemark, Agder, and Rogaland. 12

Historically, the first suggested TBEV isolate from Norway was collected in I. ricinus from Vestland County (former Sogn and Fjordane) in June 1976, as described by Traavik and co-workers. Five virus strains with a close serological relationship to the TBEV complex were detected in this study.25

One pool of ten nymphs collected from southern Norway has been whole-genome sequenced and phylogenetically characterized. This strain, \u201cMandal 2009\u201d, was found to belong to the Scandinavian group of the European TBEV subtype. Interestingly, \u201cMandal 2009\u201d revealed a shorter form of the TBEV genome within the 3\u2019 non-coding region, like the highly virulent \u201cHypr\u201d strain.20 Recent unpublished findings indicate the circulation of at least one new TBEV variant in Norway from two new areas. This variant in the TBEV sequence is detected in a tick and one patient sample, both different from the previous Mandal 2009 strain.31,32<\/sup><\/a><\/p>\n\n\n\n

Seroprevalence in animals<\/h3>\n\n\n\n

In addition to tick studies, a seroprevalence study has detected TBE antibodies in specimens from cervids (deer) collected in Farsund (Agder County) and Molde (M\u00f8re and Romsdal County). In Farsund, located on the southern coast of Norway, 41% (22 of 54 animals) were TBE-positive. This contrasts with Molde, situated midwest, where the prevalence was 1.6% (1 of 64 animals). The same study detected antibodies to Louping ill virus (LIV), a closely related flavivirus, in 14.8% (8 of 54) of the analyzed cervid sera from Farsund. 21<\/sup><\/a>

A recent seroprevalence study of cervids where serum samples were collected across Norway found TBEV antibodies in the municipalities of Steinkjer, Vindafjord, S\u00f8gne, Birkenes, Lardal, Larvik and Halden (Fig. 4). The overall seroprevalence was 4.6%. Antibodies against TBEV detected by serum neutralization test were present in 9.4% of the moose samples, 1.4% in red deer, 0.7% in roe deer, and 0% in reindeer.11<\/sup><\/a>

Ticks (6850 nymphs and 765 adults) from eastern, western, and northern Norway were analyzed for LIV using an in-house real-time polymerase chain reaction (PCR), none of these were positive (unpublished data). However, a recent study by Ytrehus et al. detected antibodies against LIV in willow ptarmigan (Lagopus lagopus lagopus) across the whole country. The study suggested that either LIV or a cross-reacting virus infects ptarmigan in Norway, also at high altitudes and latitudes. 33<\/sup><\/a>

There is limited knowledge of TBEV in domestic animals in Norway. A recent study reported TBEV RNA in unpasteurized cow milk from three farms located in southern and northern Norway in 5.4% of the tested animals. Seropositive animals were only detected at one farm in southern Norway, in 88.2% of the tested animals.10<\/sup><\/a> This is higher than in a previous study by Traavik (1973), where a seroprevalence of 17.7% was detected in bovine sera in western Norway.22<\/sup><\/a><\/p>\n\n\n\n

Seroprevalence in humans<\/h3>\n\n\n\n

In S\u00f8gne municipality, a TBE endemic area of southern Norway, a TBEV seroprevalence of 3.1% (45\/1,453) was found in the general adult population. Among individuals not vaccinated against TBEV and\/or yellow fever, the seroprevalence of IgG antibodies to TBEV was 1.4% (6\/419).33<\/sup><\/a> A recent blood donor study from TBE endemic areas in Vestfold and Telemark found a low seroprevalence of 0.4% (4\/1,123). Out of the 1,123 analyzed samples, 21 had neutralizing antibodies to TBEV, of which 17 reported a previous TBE vaccination. 32<\/sup><\/a>

Three seroprevalence studies in humans from presumed non-endemic areas have been published. Larsen et al. detected TBE immunoglobulin G (IgG) antibodies among 0.65% of blood donors in Viken County (former \u00d8stfold) in southeastern Norway.23<\/sup><\/a> The second study in 1,213 blood donors was performed in Vestland County (formerly Sogn and Fjordane), located in western Norway. TBE IgG antibodies (ELISA) were detected in five (0.4%) of these samples. However, four of these were reported to be vaccinated against flaviviruses, and one was negative by neutralization test.24<\/sup><\/a> In 1979, Traavik detected a 19.6% seroprevalence in Vestland County. However, these results were not confirmed with a neutralization test and thus may be explained by cross-reactions to LIV, vaccine-related flaviviruses, or nonspecific binding in the test.26<\/sup><\/a><\/p>\n\n\n\n

Conclusion<\/strong><\/h3>\n\n\n\n

In summary, TBE is endemic in parts of Norway and the number of human TBE cases has been increasing in recent years. Clinical TBE cases are only found in southern parts of Norway; however, the results from both prevalence studies in ticks and seroprevalence studies in humans and animals indicate that TBEV might be widespread in the country, and not limited to the southern region. This is highly relevant information for public health considerations and risk evaluation. Further studies on tick distribution and prevalence of TBEV in ticks, humans and animals in Norway are currently ongoing.<\/p>\n\n\n\n

Overview of TBE in Norway<\/strong><\/h3>\n\n\n\n\n\n\n\n \n \n \n \n
Table 1: Virus, vector, transmission of TBE in Norway<\/th>\n<\/tr>\n\n
Viral subtypes, distribution<\/td>\n \n Western subtype.

\n\n TBEV is distributed in Ixodes ricinus<\/em> ticks in the following counties: Viken, Vestfold and Telemark, Agder, Rogaland, Vestland, M\u00f8re og Romsdal, Tr\u00f8ndelag and Nordland.

\n\n Human TBE cases are reported in the following counties: Agder, Vestfold and Telemark, and Viken.3<\/sup><\/a>,7<\/sup><\/a>,8<\/sup><\/a>,10-12<\/sup><\/a>,21<\/sup><\/a>,25<\/sup><\/a>

\n\n Source: <\/em>www.fhi.no
\n Norwegian Surveillance System for Communicable Diseases (MSIS)<\/em>\n <\/td>\n<\/tr>\n\n
Reservoir animals<\/td>\n \n Small rodents in the genera Apodemus<\/em> and Myodes<\/em>.26<\/sup><\/a>\n <\/td>\n<\/tr>\n\n
Infected tick species (%)<\/td>\n \n Ixodes ricinus<\/em> (0-1.1% in nymphs and 0-20.6% in adults).10<\/sup><\/a>\n <\/td>\n<\/tr>\n\n
Dairy product transmission<\/td>\n \n Not documented.
\n TBEV RNA has been detected in unpasteurized cow milk.8<\/sup><\/a>\n <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n\n\n\n\n \n \n \n \n \n \n \n
Table 2: TBE-reporting and vaccine prevention in Norway<\/th>\n<\/tr>\n\n
Mandatory TBE reporting<\/td>\n \n Hospitals and General Practitioners.
\n Only cases with meningitis\/encephalitis are notifiable.

\n\n Criteria:
\n – Detection of specific antibody response in serum and\/or cerebrospinal fluid
\n and\/or
\n – Detection of TBEV in cerebrospinal fluid and\/or serum by isolation and nucleic acid analysis.

\n\n Source:<\/em> www.fhi.no\n <\/td>\n<\/tr>\n\n
Other TBE-surveillance<\/td>\n \n Ongoing studies:

\n\n The Barents region project (ID B1710). Emerging infections. Capacity building on vector-borne infections in the Barents Region, Norway and Russia.

\n\n EMERGING VIRUS: Vector-borne infections in Norway \u2013 Understanding the emergence of viral vector-borne diseases in a One Health perspective by studies of dynamics, distribution, climate, genetic diversity, biogeographic distribution, risk of infection, surveillance and diagnosis.

\n\n Observation and prognosis of TBE-patients (Telemark Sykehus HF).

\n\n North-Tick (Interreg VB, North Sea program): Vector-borne pathogens\/infections in the North Sea area.

\n\n Experimental infection study of sheep with TBEV: Transmission to lambs via milk.

\n\n TBFV net (EEA-project): surveillance and research on tick-borne flaviviruses.

\n\n Development of pipeline of whole genome sequencing of TBEV.30,31<\/sup><\/a>\n <\/td>\n<\/tr>\n\n
Special clinical features<\/td>\n \n No. TBE has been mandatorily notifiable to MSIS (Norwegian Surveillance System for Communicable Diseases) since 1975.1<\/sup><\/a>

\n\n Source:<\/em> www.fhi.no\n <\/td>\n<\/tr>\n\n
Available vaccines<\/td>\n \n TicoVac, Pfizer
\n TicoVac Junior, Pfizer

\n\n Source:<\/em> The Norwegian Medicines Agency\n <\/td>\n<\/tr>\n\n
Vaccination recommendations and reimbursement<\/td>\n \n People who spend a lot of time outdoors in areas with a known risk of TBE infection (Table 1) should consider TBE vaccination. This recommendation applies especially to people who often get tick bites such as forestry workers, orienteers, and others who spend much time outdoors.

\n\n There is no reimbursement in place.

\n\n Source:<\/em> www.fhi.no\n <\/td>\n<\/tr>\n\n
Vaccine uptake by age group\/risk group\/general population<\/td>\n \n In Norway, all immunizations should be registered into the national immunization register, SYSVAK. According to SYSVAK for 2024, 103,749 persons have been vaccinated against TBE and there were sold 172,355 doses, which is an increase from 2022 and 2023. There is no information about risk factors in the register.

\n\n For vaccines outside the childhood immunization program, registration into SYSVAK is consensual. The number of doses actually given therefore could be higher than the numbers registered, and this is probably the case for TBE vaccine, as the number of doses distributed is higher than the number of doses entered into the register.

\n\n Source:<\/em> Norwegian Immunisation Registry (SYSVAK)
\n Norwegian Institute of Public Health\u2019s Warehouse Management System\n <\/td>\n<\/tr>\n\n
Name, address\/website of TBE National Reference Center<\/td>\n \n Norwegian Institute of Public Health
\n www.fhi.no\n <\/td>\n<\/tr>\n\n<\/tbody>\n<\/table>\n\n\n\n
\n
\n

Figure 1:<\/span> Burden of TBE in Norway 1994-2025*. Update for 2025:
97 reported cases.<\/h3>\n<\/div>\n
\"\"<\/a><\/figure>
<\/div>\n
Source data \n\n\n\n\t\n\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t
Year<\/th>Number of cases<\/th>Incidence \/ 105<\/sup><\/th>\n<\/tr>\n<\/thead>\n
1994<\/td>2<\/td><0.1<\/td>\n<\/tr>\n
1995<\/td>0<\/td>0<\/td>\n<\/tr>\n
1996<\/td>0<\/td>0<\/td>\n<\/tr>\n
1997<\/td>0<\/td>0<\/td>\n<\/tr>\n
1998<\/td>1<\/td><0.1<\/td>\n<\/tr>\n
1999<\/td>1<\/td><0.1<\/td>\n<\/tr>\n
2000<\/td>1<\/td><0.1<\/td>\n<\/tr>\n
2001<\/td>0<\/td>0<\/td>\n<\/tr>\n
2002<\/td>2<\/td><0.1<\/td>\n<\/tr>\n
2003<\/td>1<\/td><0.1<\/td>\n<\/tr>\n
2004<\/td>4<\/td><0.1<\/td>\n<\/tr>\n
2005<\/td>4<\/td><0.1<\/td>\n<\/tr>\n
2006<\/td>5<\/td>0.1<\/td>\n<\/tr>\n
2007<\/td>13<\/td>0.2<\/td>\n<\/tr>\n
2008<\/td>11<\/td>0.2<\/td>\n<\/tr>\n
2009<\/td>10<\/td>0.2<\/td>\n<\/tr>\n
2010<\/td>11<\/td>0.2<\/td>\n<\/tr>\n
2011<\/td>14<\/td>0.3<\/td>\n<\/tr>\n
2012<\/td>7<\/td>0.1<\/td>\n<\/tr>\n
2013<\/td>6<\/td>0.1<\/td>\n<\/tr>\n
2014<\/td>13<\/td>0.2<\/td>\n<\/tr>\n
2015<\/td>9<\/td>0.2<\/td>\n<\/tr>\n
2016<\/td>12<\/td>0.2<\/td>\n<\/tr>\n
2017<\/td>16<\/td>0.3<\/td>\n<\/tr>\n
2018<\/td>26<\/td>0.5<\/td>\n<\/tr>\n
2019<\/td>35<\/td>0.7<\/td>\n<\/tr>\n
2020<\/td>41<\/td>0.8<\/td>\n<\/tr>\n
2021<\/td>71<\/td>1.3<\/td>\n<\/tr>\n
2022<\/td>90<\/td>1.6<\/td>\n<\/tr>\n
2023<\/td>113<\/td>2.0<\/td>\n<\/tr>\n
2024<\/td>76<\/td>1.4<\/td>\n<\/tr>\n
2025<\/td>97<\/td>1.7<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/a><\/div>\n
*data per February 2024 (MSIS). These data include 99 cases that have been infected abroad or have an unknown infection history. The 1997 case was registered in 1998.<\/em><\/div>
\n<\/div>
\n\n\n\n
\n
\n

Figure 2:<\/span> Age and gender distribution of TBE in Norway 1994-2025*<\/h3>\n<\/div>\n
\"\"<\/a><\/figure>
<\/div>\n
Source data \n\n\n\n\t\n\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t
Age groups (years)<\/th>Females<\/th>Males<\/th>All<\/th>\n<\/tr>\n<\/thead>\n
0-9<\/td>4<\/td>10<\/td>14<\/td>\n<\/tr>\n
10-19<\/td>18<\/td>21<\/td>39<\/td>\n<\/tr>\n
20-29<\/td>15<\/td>15<\/td>30<\/td>\n<\/tr>\n
30-39<\/td>19<\/td>41<\/td>60<\/td>\n<\/tr>\n
40-49<\/td>33<\/td>70<\/td>103<\/td>\n<\/tr>\n
50-59<\/td>46<\/td>54<\/td>100<\/td>\n<\/tr>\n
60-69<\/td>28<\/td>61<\/td>89<\/td>\n<\/tr>\n
70+<\/td>35<\/td>49<\/td>84<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/a><\/div>\n
*data per March, 2026. 4 (MSIS). These data include 99 cases that have been infected abroad or have an unknown infection history.<\/em><\/div>
\n<\/div>
\n\n\n\n
\n
\n

Figure 3:<\/span> TBE cases in Norway 1994-2024 (MSIS) <\/h3>\n<\/div>\n
\"\"<\/a><\/figure>
<\/div>\n
Source: https:\/\/www.fhi.no\/sm\/smittevernveilederen\/sykdommer-a-a\/skogflattencefalitt-tbe-virusinfeksjoner\/?term=#forekomst-i-norge<\/em><\/div>
\n<\/div>
\n\n\n\n
\n\n
\n

\n Figure 4:<\/span>\n Geographical locations where tick-borne encephalitis virus has been detected in Norway from 2004 to 2020.\n <\/h3>\n <\/div>\n\n
\n \n \"\"\n <\/a>\n <\/figure>\n\n

\n \u25cf<\/span> No ticks found,\n \u25cf<\/span> Ticks with TBEV,\n \u25cf<\/span> TBEV antibodies in animals,\n \u25c9<\/span> TBEV in ticks, cow milk, and TBEV antibodies in animals,\n \u25cf<\/span> Site where Ixodes persulcatus<\/em> have been detected in 2023.\n <\/p>\n\n

\n Map from \u00a9 Kartverket Attribution 4.0 International (CC BY 4.0) [3<\/sup><\/a>,\n7<\/sup><\/a>–10<\/sup><\/a>,\n19<\/sup><\/a>,\n21<\/sup><\/a>,\n25<\/sup><\/a>].\n <\/div>\n\n<\/div>\n\n\n\n
\n
\n

Figure 5:<\/span> Expanded geographical distribution of reported TBE cases in Norway between 2009 and 2025. The red line shows the distribution border in 2009, the areas north and east of this, represents areas where new cases have been reported after 2009. <\/h3>\n<\/div>\n
\"\"<\/a><\/figure>
<\/div>\n<\/div>\n\n\n\n
\n
\n

\n Table 3:<\/span>\n Overview of monthly reported TBE cases 2025\n <\/h3>\n <\/div>\n\n \n\n\n\n\t\n\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t
Month <\/th>Infected in Norway<\/th>Unknown infection site<\/th>Infected abroad<\/th>Total 2025<\/th>Total 1994-2025<\/th>\n<\/tr>\n<\/thead>\n
January <\/td><\/td>1<\/td><\/td>1<\/td>2<\/td>\n<\/tr>\n
April<\/td>3<\/td><\/td><\/td>3<\/td>4<\/td>\n<\/tr>\n
May<\/td>5<\/td>1<\/td>1<\/td>10<\/td>42<\/td>\n<\/tr>\n
June<\/td>9<\/td>3<\/td><\/td>12<\/td>75<\/td>\n<\/tr>\n
July<\/td>14<\/td>4<\/td>1<\/td>19<\/td>128<\/td>\n<\/tr>\n
August<\/td>17<\/td><\/td><\/td>19<\/td>167<\/td>\n<\/tr>\n
September<\/td>12<\/td><\/td>2<\/td>12<\/td>139<\/td>\n<\/tr>\n
October<\/td>12<\/td>1<\/td><\/td>13<\/td>99<\/td>\n<\/tr>\n
November<\/td>7<\/td><\/td><\/td>7<\/td>31<\/td>\n<\/tr>\n
December<\/td>1<\/td><\/td><\/td>1<\/td>5<\/td>\n<\/tr>\n
Total 2025<\/td>80<\/td>10<\/td>4<\/td>97<\/td>692<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n
\n Appendix<\/span>
\n Source data: Figure 1<\/span>\n <\/div>\n<\/div>\n
\n\n\n\n

Acknowledgments<\/h3>\n\n\n\n

We thank Trude Marie Lyngstad for making Figure 3.<\/p>\n\n\n\n

Contact<\/strong><\/h3>\n\n\n\nAshildKristine.Andreassen@fhi.no<\/a>;\nandrea.perdomo@usn.no<\/a>;\nArnulf.soleng@Hdir.no<\/a>;\nurushamaharjan111@gmail.com<\/a>;\nHeidi.Lindstedt@Hdir.no<\/a>;\nKristian.alfsnes@fhi.no<\/a>;\nRikard.Rykkvin@fhi.no<\/a>\n\n\n\n

Authors and Affiliation <\/h3>\n\n\n\n

\u00c5shild K. Andreassen<\/a>, Andrea P. Cotes-Perdomo<\/a>, Arnulf Soleng<\/a>, Urusha Maharjan<\/a>, Heidi H. Lindstedt<\/a>, Kristian Alfsnes<\/a>, and Kristian Alfsnes<\/a>
Norwegian Institute of Public Health, Department of Virology<\/p>\n\n\n\n

Kristian Alfsnes<\/a>
Norwegian Institute of Public Health, Department of Bacteriology<\/p>\n\n\n\n

Citation<\/strong><\/h3>\n\n\n\n

Andreassen KA, Cotes-Perdomo AP, Soleng A, Maharjan U, Lindstedt HH, Alfsnes K, Rykkvin R. TBE in Norway. In: Dobler G, Erber W, Br\u00f6ker M, Chitimia-Dobler L, Schmitt HJ, eds. The TBE Book. 9th ed. Singapore: Global Health Press; 2026. doi:10.33442\/26613980_13-24-9<\/p>\n\n\n\n

References<\/strong><\/h3>\n\n\n\n
    \n
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  4. <\/a>Soleng A, Paulsen KM, Pedersen BN, et al. Distribution of Ixodes ricinus ticks and prevalence of tick-borne encephalitis virus among questing ticks in the Arctic Circle region of northern Norway. Ticks Tick Borne Dis<\/em>. 2018;9(1):97-103. doi:10.1016\/j.ttbdis.2017.10.002<\/li>\n\n
  5. <\/a>Hvidsten D, Frafjord K, Gray JS, et al. The distribution limit of the common tick, Ixodes ricinus, and some associated pathogens in northwestern Europe. Ticks Tick Borne Dis<\/em>. 2020;11(3):101388. doi:10.1016\/j.ttbdis.2020.101388<\/li>\n\n
  6. <\/a>Hvidsten D, Stuen S, Jenkins A, Dienus O, Olsen RS, Kristiansen BE, Mehl R, Matussek A. Ixodes ricinus and Borrelia prevalence at the Arctic Circle in Norway. Ticks Tick Borne Dis<\/em>. 2014;5(2):107-112. doi:10.1016\/j.ttbdis.2013.09.003<\/li>\n\n
  7. <\/a>Jore S, Viljugrein H, Hofshagen M, et al. Multi-source analysis reveals latitudinal and altitudinal shifts in range of Ixodes ricinus at its northern distribution limit. Parasit Vectors<\/em>. 2011;4:84.<\/li>\n\n
  8. <\/a>Jenkins A, Hvidsten D, Matussek A, Lindgren PE, Stuen S, Kristiansen BE. Borrelia burgdorferi sensu lato in Ixodes ricinus ticks from Norway: evaluation of a PCR test targeting the chromosomal flaB gene. Exp Appl Acarol<\/em>. 2012;58(4):431-439. doi:10.1007\/s10493-012-9585-2<\/li>\n\n
  9. <\/a>Paulsen KM, Pedersen BN, Soleng A, et al. Prevalence of tick-borne encephalitis virus in Ixodes ricinus ticks from three islands in north-western Norway. APMIS<\/em>. 2015;123(9):759-764. doi:10.1111\/apm.12412<\/li>\n\n
  10. <\/a>Paulsen KM, Stuen S, das Neves CG, et al. Tick-borne encephalitis virus in cows and unpasteurized cow milk from Norway. Zoonoses Public Health<\/em>. 2019;66(2):216-222. doi:10.1111\/zph.12554<\/li>\n\n
  11. <\/a>Paulsen KM, das Neves CG, Granquist EG, Madslien K, Stuen S, Pedersen BN, Vikse R, Rocchi M, Laming E, Stiasny K, Andreassen AK. Cervids as sentinel species for tick-borne encephalitis virus in Norway: a serological study. Zoonoses Public Health<\/em>. 2019;66(8):849-857. doi:10.1111\/zph.12675<\/li>\n\n
  12. <\/a>Vikse R, Paulsen KM, Edgar KS, et al. Geographical distribution and prevalence of tick-borne encephalitis virus in questing Ixodes ricinus ticks and phylogeographic structure of the Ixodes ricinus vector in Norway. Zoonoses Public Health<\/em>. 2020;67(4):370-381. doi:10.1111\/zph.12696<\/li>\n\n
  13. <\/a>Skarpaas T, Lj\u00f8stad U, Sund\u00f8y A. First human cases of tick-borne encephalitis, Norway. Emerg Infect Dis<\/em>. 2004;10(12):2241-2243. doi:10.3201\/eid1012.040598<\/li>\n\n
  14. <\/a>Skarpaas T, Golovljova I, Vene S, Lj\u00f8stad U, Sjursen H, Plyusnin A, Lundkvist A. Tick-borne encephalitis virus, Norway and Denmark. Emerg Infect Dis<\/em>. 2006;12(7):1136-1138. doi:10.3201\/eid1207.051567<\/li>\n\n
  15. <\/a>Cs\u00e1ng\u00f3 PA, Blakstad E, Kirtz GC, Pedersen JE, Czettel B. Tick-borne encephalitis in southern Norway. Emerg Infect Dis<\/em>. 2004;10(3):533-534. doi:10.3201\/eid1003.020734<\/li>\n\n
  16. <\/a>Andreassen A, Jore S, Cuber P, et al. Prevalence of tick-borne encephalitis virus in tick nymphs in relation to climatic factors on the southern coast of Norway. Parasit Vectors<\/em>. 2012;5:177. doi:10.1186\/1756-3305-5-177<\/li>\n\n
  17. <\/a>Norwegian Surveillance System for Communicable Diseases (MSIS). Norwegian Institute of Public Health. Accessed October 31, 2019. https:\/\/www.msis.no<\/li>\n\n
  18. <\/a>Radzisauskiene D, Zagminas K, Asokliene L, et al. Epidemiological patterns of tick-borne encephalitis in Lithuania and clinical features in adults in light of the high incidence in recent years: a retrospective study. Eur J Neurol<\/em>. 2018;25(2):268-274. doi:10.1111\/ene.13486<\/li>\n\n
  19. <\/a>Kaminski M, Grummel V, Hoffmann D, Berthele A, Hemmer B. The spectrum of aseptic central nervous system infections in southern Germany: demographic, clinical and laboratory findings. Eur J Neurol<\/em>. 2017;24(8):1062-1070. doi:10.1111\/ene.13335<\/li>\n\n
  20. <\/a>Asghar N, Lindblom P, Melik W, et al. Tick-borne encephalitis virus sequenced directly from questing and blood-feeding ticks reveals quasispecies variance. PLoS One<\/em>. 2014;9(7):e103264. doi:10.1371\/journal.pone.0103264<\/li>\n\n
  21. <\/a>Ytrehus B, Vainio K, Dudman SG, Gilray J, Willoughby K. Tick-borne encephalitis virus and louping-ill virus may co-circulate in southern Norway. Vector Borne Zoonotic Dis<\/em>. 2013;13(10):762-768. doi:10.1089\/vbz.2012.1023<\/li>\n\n
  22. <\/a>Traavik T. Serological investigations indicating the existence of tick-borne encephalitis virus foci along the Norwegian coast. Acta Pathol Microbiol Scand B<\/em>. 1973;81(1):138-142. doi:10.1111\/j.1699-0463.1973.tb02197.x<\/li>\n\n
  23. <\/a>Larsen AL, Kanestr\u00f8m A, Bjorland M, Andreassen A, Soleng A, Vene S, Dudman SG. Detection of specific IgG antibodies in blood donors and tick-borne encephalitis virus in ticks within a non-endemic area in southeast Norway. Scand J Infect Dis<\/em>. 2014;46(3):181-184. doi:10.3109\/00365548.2013.865140<\/li>\n\n
  24. <\/a>Hjetland R, Henningsson AJ, Vainio K, Dudman SG, Grude N, Ulvestad E. Seroprevalence of antibodies to tick-borne encephalitis virus and Anaplasma phagocytophilum in healthy adults from western Norway. Infect Dis (Lond)<\/em>. 2015;47(1):52-56. doi:10.3109\/00365548.2014.959044<\/li>\n\n
  25. <\/a>Traavik T, Mehl R, Wiger R. The first tick-borne encephalitis virus isolates from Norway. Acta Pathol Microbiol Scand B<\/em>. 1978;86(4):253-255. doi:10.1111\/j.1699-0463.1978.tb00040.x<\/li>\n\n
  26. <\/a>Traavik T. Antibodies to tick-borne encephalitis virus in human sera from the western coast of Norway. Acta Pathol Microbiol Scand B<\/em>. 1979;87B(1):9-13. doi:10.1111\/j.1699-0463.1979.tb02396.x<\/li>\n\n
  27. <\/a>Kjelland V, Paulsen KM, Rollum R, et al. Tick-borne encephalitis virus, Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Anaplasma phagocytophilum and Candidatus Neoehrlichia mikurensis in Ixodes ricinus ticks collected from recreational islands in southern Norway. Ticks Tick Borne Dis<\/em>. 2018;9(5):1098-1102.<\/li>\n\n
  28. <\/a>Jaenson TGT, Hjertqvist M, Bergstr\u00f6m T, Lundkvist \u00c5. Why is tick-borne encephalitis increasing? A review of the key factors causing the increasing incidence of human TBE in Sweden. Parasit Vectors<\/em>. 2012;5:184. doi:10.1186\/1756-3305-5-184<\/li>\n\n
  29. <\/a>Cotes-Perdomo A, Soleng A, Alfsnes K, Andreassen \u00c5. First report of the taiga tick Ixodes persulcatus in Norway. Ticks Tick Borne Dis<\/em>. 2025;16(4):102508. doi:10.1016\/j.ttbdis.2025.102508<\/li>\n\n
  30. <\/a>Maharjan U, Skudal HK, Asghar N, et al. Novel variants of tick-borne encephalitis virus from patient and tick samples in Norway. Ticks Tick Borne Dis<\/em>. 2025;16(4):102501. doi:10.1016\/j.ttbdis.2025.102501<\/li>\n\n
  31. <\/a>Holten AR, Bjerkhaug AW, Maharjan U, et al. A case of fatal hemorrhagic fever associated with tick-borne encephalitis virus infection. Int J Infect Dis<\/em>. 2025;159:107989. doi:10.1016\/j.ijid.2025.107989<\/li>\n\n
  32. <\/a>Thortveit ET, Aase A, Petersen LB, Lorentzen \u00c5R, Mygland \u00c5, Lj\u00f8stad U. Human seroprevalence of antibodies to tick-borne microbes in southern Norway. Ticks Tick Borne Dis<\/em>. 2020;11(4):101410. doi:10.1016\/j.ttbdis.2020.101410<\/li>\n\n
  33. <\/a>Ytrehus B, Rocchi M, Brandsegg H, Turnbull D, Miller A, Pedersen HC, K\u00e5l\u00e5s JA, Nilsen EB. Louping-ill virus serosurvey of willow ptarmigan (Lagopus lagopus lagopus) in Norway. J Wildl Dis<\/em>. 2021;57(2):282-291. doi:10.7589\/JWD-D-20-00068<\/li>\n<\/ol>\n<\/span>","protected":false},"excerpt":{"rendered":"

    TBE in Norway \u00c5shild K. Andreassen, Andrea P. Cotes-Perdomo, Arnulf Soleng,Urusha Maharjan, Heidi H. Lindstedt, Kristian Alfsnes, and Rikard Rykkvin (last edited in June 2026, update for 2024: 78 reported cases; update for 2025: 97 reported cases) History and current situation In Norway, tick-borne encephalitis (TBE) has been a mandatory notifiable disease since 1975 (Norwegian Surveillance System for Communicable Diseases, MSIS).1 According to ECDC’s classification, coastal areas in southern Norway (counties of Agder, Vestfold and Telemark) are endemic for TBE. Further, the counties of \u00d8stfold, Akershus, and Buskerud, and western and northern Norway to Br\u00f8nn\u00f8y municipality are imperiled.2-12 The first reported case of TBE occurred in 1997 at Trom\u00f8y in Agder County.13 This is a region with holiday cabins and outdoor recreation areas for both local inhabitants and tourists, and it is known for high temperatures during spring and summer. In addition, TBE antibodies in dogs and tick-borne encephalitis virus (TBEV) in ticks have been detected in this area.10,12-15 A total number of TBE cases have been reported to MSIS as of February 2025 (Fig. 1). Of these, the majority are autochthonous infections, while the remainder were infected abroad or have an unknown infection history. The number of cases varies annually between 1 and 97 (Table 1 and Fig. 1). Data from 2018 to 2025 show an increase in the number of reported cases, especially in the counties of Vestfold and Telemark (Fig. 5). In 2023, the first case from Vestland County was reported to MSIS. The TBE patients\u2019 age distribution is in accordance with other European studies, with a higher infection rate among those older than 30 years (Table 2 and Fig. 2).16\u201317 According to MSIS, the reported cases in Norway are represented mainly by the counties of Agder, Vestfold and Telemark, and Viken, all located in the southern part of the country (Fig. 3). No cases are reported from the northern coastal areas, although a few cases are reported from the western areas and the area east of the Oslofjord, despite outdoor recreational activities being common throughout the country. Ticks and TBEV in Norway The castor bean tick (Ixodes ricinus) is the most common tick species in Europe,18 and considered to be the major vector of the European TBE-virus.19-20 The geographical distribution of I. ricinus in Norway has been investigated in several studies.2-4,10,21-25 Both Tambs-Lyche (1943) and Mehl (1983) found I. ricinus to be mainly distributed in the coastal areas of Norway, from the southeastern border to Sweden, along the southern and western coastline, up to Nordland County at ~65.1\u00b0N.2,3,21-25 The density of ticks varies between locations, even when separated by short distances. This is probably caused by differences in microclimatic conditions, vegetation, and density of vertebrate hosts. However, locations with a high density of ticks are found all over the major distributional range. The density of ticks declines rapidly with both increasing distance from the coast and increasing altitude. In a multi-source study, Jore et al. (2011) suggested that tick populations in Norway had undergone recent shifts in latitudinal and altitudinal range.7 This result is, however, disputed in recent studies.4,5 Although ticks are reported far outside (i.e. northeast) of the hitherto established distribution limit of I. ricinus in Norway, the vast majority of these are engorged females.24-26 Migratory birds may deposit engorged larvae or nymphs in areas where temperatures permit development to the next stage but not completion of the life cycle. Thus, such records do not constitute evidence for established and sustainable tick populations as this requires the presence of all the active stages (larvae, nymphs, and adults) in a locality for at least two consecutive seasons.27,28 Using flagging and dragging, Soleng et al. (2018) found tick larvae, nymphs and adults to be abundant at 64.5 and 65.1\u00b0N. Only a few tick nymphs and adults, and no larvae, were found at locations close to 66\u00b0N. At several locations from 66.3\u00b0N up to 67.5\u00b0N no ticks were found.3 In a recent study by Hvidsten et al. (2020), the occurrence of ticks in northern Norway was examined by dragging in 109 separate locations between the latitudes of 64\u00b0N and 70\u00b0N. The northernmost location with a permanent I. ricinus population was at 66.2\u00b0N on the Island of D\u00f8nna (Fig. 4).5,6 It is noteworthy that the taiga tick (Ixodes persulcatus) and the meadow tick (Dermacentor reticulatus) were not detected in a large screening of ticks collected in the southern part of Norway in 2016.29 Studies of I. ricinus in Norway have detected TBEV in nymphs with a prevalence ranging from 0% to 1.1%. In adult ticks collected from the same areas, the prevalence ranges from 0% to 20.6%. TBEV positive ticks have been found in sampling areas along the Norwegian coastline from the east of \u00d8stfold County to Br\u00f8nn\u00f8y in Nordland County.12 The highest estimated TBEV prevalence in adult ticks has been found in the counties of Rogaland and Vestfold and Telemark. In nymphs, the highest prevalence has been found in Vestfold, Telemark, Agder, and Rogaland. 12 Historically, the first suggested TBEV isolate from Norway was collected in I. ricinus from Vestland County (former Sogn and Fjordane) in June 1976, as described by Traavik and co-workers. Five virus strains with a close serological relationship to the TBEV complex were detected in this study.25 One pool of ten nymphs collected from southern Norway has been whole-genome sequenced and phylogenetically characterized. This strain, \u201cMandal 2009\u201d, was found to belong to the Scandinavian group of the European TBEV subtype. Interestingly, \u201cMandal 2009\u201d revealed a shorter form of the TBEV genome within the 3\u2019 non-coding region, like the highly virulent \u201cHypr\u201d strain.20 Recent unpublished findings indicate the circulation of at least one new TBEV variant in Norway from two new areas. This variant in the TBEV sequence is detected in a tick and one patient sample, both different from the previous Mandal 2009 strain.31,32 Seroprevalence in animals In addition to tick studies, a seroprevalence study has detected TBE antibodies in specimens from cervids (deer) collected in Farsund (Agder County) and Molde (M\u00f8re and<\/p>\n","protected":false},"author":94681,"featured_media":12842,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[1],"tags":[],"coauthors":[1108],"class_list":["post-28360","post","type-post","status-publish","format-standard","has-post-thumbnail","category-uncategorized"],"yoast_head":"\nNorway - TBE Book<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/tbenews.com\/tbe\/13-24-9\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Norway - TBE Book\" \/>\n<meta property=\"og:description\" content=\"TBE in Norway \u00c5shild K. Andreassen, Andrea P. Cotes-Perdomo, Arnulf Soleng,Urusha Maharjan, Heidi H. Lindstedt, Kristian Alfsnes, and Rikard Rykkvin (last edited in June 2026, update for 2024: 78 reported cases; update for 2025: 97 reported cases) History and current situation In Norway, tick-borne encephalitis (TBE) has been a mandatory notifiable disease since 1975 (Norwegian Surveillance System for Communicable Diseases, MSIS).1 According to ECDC’s classification, coastal areas in southern Norway (counties of Agder, Vestfold and Telemark) are endemic for TBE. Further, the counties of \u00d8stfold, Akershus, and Buskerud, and western and northern Norway to Br\u00f8nn\u00f8y municipality are imperiled.2-12 The first reported case of TBE occurred in 1997 at Trom\u00f8y in Agder County.13 This is a region with holiday cabins and outdoor recreation areas for both local inhabitants and tourists, and it is known for high temperatures during spring and summer. In addition, TBE antibodies in dogs and tick-borne encephalitis virus (TBEV) in ticks have been detected in this area.10,12-15 A total number of TBE cases have been reported to MSIS as of February 2025 (Fig. 1). Of these, the majority are autochthonous infections, while the remainder were infected abroad or have an unknown infection history. The number of cases varies annually between 1 and 97 (Table 1 and Fig. 1). Data from 2018 to 2025 show an increase in the number of reported cases, especially in the counties of Vestfold and Telemark (Fig. 5). In 2023, the first case from Vestland County was reported to MSIS. The TBE patients\u2019 age distribution is in accordance with other European studies, with a higher infection rate among those older than 30 years (Table 2 and Fig. 2).16\u201317 According to MSIS, the reported cases in Norway are represented mainly by the counties of Agder, Vestfold and Telemark, and Viken, all located in the southern part of the country (Fig. 3). No cases are reported from the northern coastal areas, although a few cases are reported from the western areas and the area east of the Oslofjord, despite outdoor recreational activities being common throughout the country. Ticks and TBEV in Norway The castor bean tick (Ixodes ricinus) is the most common tick species in Europe,18 and considered to be the major vector of the European TBE-virus.19-20 The geographical distribution of I. ricinus in Norway has been investigated in several studies.2-4,10,21-25 Both Tambs-Lyche (1943) and Mehl (1983) found I. ricinus to be mainly distributed in the coastal areas of Norway, from the southeastern border to Sweden, along the southern and western coastline, up to Nordland County at ~65.1\u00b0N.2,3,21-25 The density of ticks varies between locations, even when separated by short distances. This is probably caused by differences in microclimatic conditions, vegetation, and density of vertebrate hosts. However, locations with a high density of ticks are found all over the major distributional range. The density of ticks declines rapidly with both increasing distance from the coast and increasing altitude. In a multi-source study, Jore et al. (2011) suggested that tick populations in Norway had undergone recent shifts in latitudinal and altitudinal range.7 This result is, however, disputed in recent studies.4,5 Although ticks are reported far outside (i.e. northeast) of the hitherto established distribution limit of I. ricinus in Norway, the vast majority of these are engorged females.24-26 Migratory birds may deposit engorged larvae or nymphs in areas where temperatures permit development to the next stage but not completion of the life cycle. Thus, such records do not constitute evidence for established and sustainable tick populations as this requires the presence of all the active stages (larvae, nymphs, and adults) in a locality for at least two consecutive seasons.27,28 Using flagging and dragging, Soleng et al. (2018) found tick larvae, nymphs and adults to be abundant at 64.5 and 65.1\u00b0N. Only a few tick nymphs and adults, and no larvae, were found at locations close to 66\u00b0N. At several locations from 66.3\u00b0N up to 67.5\u00b0N no ticks were found.3 In a recent study by Hvidsten et al. (2020), the occurrence of ticks in northern Norway was examined by dragging in 109 separate locations between the latitudes of 64\u00b0N and 70\u00b0N. The northernmost location with a permanent I. ricinus population was at 66.2\u00b0N on the Island of D\u00f8nna (Fig. 4).5,6 It is noteworthy that the taiga tick (Ixodes persulcatus) and the meadow tick (Dermacentor reticulatus) were not detected in a large screening of ticks collected in the southern part of Norway in 2016.29 Studies of I. ricinus in Norway have detected TBEV in nymphs with a prevalence ranging from 0% to 1.1%. In adult ticks collected from the same areas, the prevalence ranges from 0% to 20.6%. TBEV positive ticks have been found in sampling areas along the Norwegian coastline from the east of \u00d8stfold County to Br\u00f8nn\u00f8y in Nordland County.12 The highest estimated TBEV prevalence in adult ticks has been found in the counties of Rogaland and Vestfold and Telemark. In nymphs, the highest prevalence has been found in Vestfold, Telemark, Agder, and Rogaland. 12 Historically, the first suggested TBEV isolate from Norway was collected in I. ricinus from Vestland County (former Sogn and Fjordane) in June 1976, as described by Traavik and co-workers. Five virus strains with a close serological relationship to the TBEV complex were detected in this study.25 One pool of ten nymphs collected from southern Norway has been whole-genome sequenced and phylogenetically characterized. This strain, \u201cMandal 2009\u201d, was found to belong to the Scandinavian group of the European TBEV subtype. Interestingly, \u201cMandal 2009\u201d revealed a shorter form of the TBEV genome within the 3\u2019 non-coding region, like the highly virulent \u201cHypr\u201d strain.20 Recent unpublished findings indicate the circulation of at least one new TBEV variant in Norway from two new areas. This variant in the TBEV sequence is detected in a tick and one patient sample, both different from the previous Mandal 2009 strain.31,32 Seroprevalence in animals In addition to tick studies, a seroprevalence study has detected TBE antibodies in specimens from cervids (deer) collected in Farsund (Agder County) and Molde (M\u00f8re and\" \/>\n<meta property=\"og:url\" content=\"https:\/\/tbenews.com\/tbe\/13-24-9\/\" \/>\n<meta property=\"og:site_name\" content=\"TBE Book\" \/>\n<meta property=\"article:published_time\" content=\"2026-06-06T05:01:36+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-06-23T09:34:04+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/tbenews.com\/tbe\/wp-content\/uploads\/2017\/07\/Norway.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1180\" \/>\n\t<meta property=\"og:image:height\" content=\"250\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"logesan\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"logesan\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"17 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/13-24-9\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/13-24-9\\\/\"},\"author\":{\"name\":\"logesan\",\"@id\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/#\\\/schema\\\/person\\\/eea00490409f8d848a28485d0f68fac3\"},\"headline\":\"Norway\",\"datePublished\":\"2026-06-06T05:01:36+00:00\",\"dateModified\":\"2026-06-23T09:34:04+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/13-24-9\\\/\"},\"wordCount\":3296,\"publisher\":{\"@id\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/13-24-9\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/wp-content\\\/uploads\\\/2017\\\/07\\\/Norway.jpg\",\"inLanguage\":\"en-US\"},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/13-24-9\\\/\",\"url\":\"https:\\\/\\\/tbenews.com\\\/tbe\\\/13-24-9\\\/\",\"name\":\"Norway - 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TBE Book","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/tbenews.com\/tbe\/13-24-9\/","og_locale":"en_US","og_type":"article","og_title":"Norway - TBE Book","og_description":"TBE in Norway \u00c5shild K. Andreassen, Andrea P. Cotes-Perdomo, Arnulf Soleng,Urusha Maharjan, Heidi H. Lindstedt, Kristian Alfsnes, and Rikard Rykkvin (last edited in June 2026, update for 2024: 78 reported cases; update for 2025: 97 reported cases) History and current situation In Norway, tick-borne encephalitis (TBE) has been a mandatory notifiable disease since 1975 (Norwegian Surveillance System for Communicable Diseases, MSIS).1 According to ECDC’s classification, coastal areas in southern Norway (counties of Agder, Vestfold and Telemark) are endemic for TBE. Further, the counties of \u00d8stfold, Akershus, and Buskerud, and western and northern Norway to Br\u00f8nn\u00f8y municipality are imperiled.2-12 The first reported case of TBE occurred in 1997 at Trom\u00f8y in Agder County.13 This is a region with holiday cabins and outdoor recreation areas for both local inhabitants and tourists, and it is known for high temperatures during spring and summer. In addition, TBE antibodies in dogs and tick-borne encephalitis virus (TBEV) in ticks have been detected in this area.10,12-15 A total number of TBE cases have been reported to MSIS as of February 2025 (Fig. 1). Of these, the majority are autochthonous infections, while the remainder were infected abroad or have an unknown infection history. The number of cases varies annually between 1 and 97 (Table 1 and Fig. 1). Data from 2018 to 2025 show an increase in the number of reported cases, especially in the counties of Vestfold and Telemark (Fig. 5). In 2023, the first case from Vestland County was reported to MSIS. The TBE patients\u2019 age distribution is in accordance with other European studies, with a higher infection rate among those older than 30 years (Table 2 and Fig. 2).16\u201317 According to MSIS, the reported cases in Norway are represented mainly by the counties of Agder, Vestfold and Telemark, and Viken, all located in the southern part of the country (Fig. 3). No cases are reported from the northern coastal areas, although a few cases are reported from the western areas and the area east of the Oslofjord, despite outdoor recreational activities being common throughout the country. Ticks and TBEV in Norway The castor bean tick (Ixodes ricinus) is the most common tick species in Europe,18 and considered to be the major vector of the European TBE-virus.19-20 The geographical distribution of I. ricinus in Norway has been investigated in several studies.2-4,10,21-25 Both Tambs-Lyche (1943) and Mehl (1983) found I. ricinus to be mainly distributed in the coastal areas of Norway, from the southeastern border to Sweden, along the southern and western coastline, up to Nordland County at ~65.1\u00b0N.2,3,21-25 The density of ticks varies between locations, even when separated by short distances. This is probably caused by differences in microclimatic conditions, vegetation, and density of vertebrate hosts. However, locations with a high density of ticks are found all over the major distributional range. The density of ticks declines rapidly with both increasing distance from the coast and increasing altitude. In a multi-source study, Jore et al. (2011) suggested that tick populations in Norway had undergone recent shifts in latitudinal and altitudinal range.7 This result is, however, disputed in recent studies.4,5 Although ticks are reported far outside (i.e. northeast) of the hitherto established distribution limit of I. ricinus in Norway, the vast majority of these are engorged females.24-26 Migratory birds may deposit engorged larvae or nymphs in areas where temperatures permit development to the next stage but not completion of the life cycle. Thus, such records do not constitute evidence for established and sustainable tick populations as this requires the presence of all the active stages (larvae, nymphs, and adults) in a locality for at least two consecutive seasons.27,28 Using flagging and dragging, Soleng et al. (2018) found tick larvae, nymphs and adults to be abundant at 64.5 and 65.1\u00b0N. Only a few tick nymphs and adults, and no larvae, were found at locations close to 66\u00b0N. At several locations from 66.3\u00b0N up to 67.5\u00b0N no ticks were found.3 In a recent study by Hvidsten et al. (2020), the occurrence of ticks in northern Norway was examined by dragging in 109 separate locations between the latitudes of 64\u00b0N and 70\u00b0N. The northernmost location with a permanent I. ricinus population was at 66.2\u00b0N on the Island of D\u00f8nna (Fig. 4).5,6 It is noteworthy that the taiga tick (Ixodes persulcatus) and the meadow tick (Dermacentor reticulatus) were not detected in a large screening of ticks collected in the southern part of Norway in 2016.29 Studies of I. ricinus in Norway have detected TBEV in nymphs with a prevalence ranging from 0% to 1.1%. In adult ticks collected from the same areas, the prevalence ranges from 0% to 20.6%. TBEV positive ticks have been found in sampling areas along the Norwegian coastline from the east of \u00d8stfold County to Br\u00f8nn\u00f8y in Nordland County.12 The highest estimated TBEV prevalence in adult ticks has been found in the counties of Rogaland and Vestfold and Telemark. In nymphs, the highest prevalence has been found in Vestfold, Telemark, Agder, and Rogaland. 12 Historically, the first suggested TBEV isolate from Norway was collected in I. ricinus from Vestland County (former Sogn and Fjordane) in June 1976, as described by Traavik and co-workers. Five virus strains with a close serological relationship to the TBEV complex were detected in this study.25 One pool of ten nymphs collected from southern Norway has been whole-genome sequenced and phylogenetically characterized. This strain, \u201cMandal 2009\u201d, was found to belong to the Scandinavian group of the European TBEV subtype. Interestingly, \u201cMandal 2009\u201d revealed a shorter form of the TBEV genome within the 3\u2019 non-coding region, like the highly virulent \u201cHypr\u201d strain.20 Recent unpublished findings indicate the circulation of at least one new TBEV variant in Norway from two new areas. This variant in the TBEV sequence is detected in a tick and one patient sample, both different from the previous Mandal 2009 strain.31,32 Seroprevalence in animals In addition to tick studies, a seroprevalence study has detected TBE antibodies in specimens from cervids (deer) collected in Farsund (Agder County) and Molde (M\u00f8re and","og_url":"https:\/\/tbenews.com\/tbe\/13-24-9\/","og_site_name":"TBE Book","article_published_time":"2026-06-06T05:01:36+00:00","article_modified_time":"2026-06-23T09:34:04+00:00","og_image":[{"width":1180,"height":250,"url":"https:\/\/tbenews.com\/tbe\/wp-content\/uploads\/2017\/07\/Norway.jpg","type":"image\/jpeg"}],"author":"logesan","twitter_card":"summary_large_image","twitter_misc":{"Written by":"logesan","Est. reading time":"17 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/tbenews.com\/tbe\/13-24-9\/#article","isPartOf":{"@id":"https:\/\/tbenews.com\/tbe\/13-24-9\/"},"author":{"name":"logesan","@id":"https:\/\/tbenews.com\/tbe\/#\/schema\/person\/eea00490409f8d848a28485d0f68fac3"},"headline":"Norway","datePublished":"2026-06-06T05:01:36+00:00","dateModified":"2026-06-23T09:34:04+00:00","mainEntityOfPage":{"@id":"https:\/\/tbenews.com\/tbe\/13-24-9\/"},"wordCount":3296,"publisher":{"@id":"https:\/\/tbenews.com\/tbe\/#organization"},"image":{"@id":"https:\/\/tbenews.com\/tbe\/13-24-9\/#primaryimage"},"thumbnailUrl":"https:\/\/tbenews.com\/tbe\/wp-content\/uploads\/2017\/07\/Norway.jpg","inLanguage":"en-US"},{"@type":"WebPage","@id":"https:\/\/tbenews.com\/tbe\/13-24-9\/","url":"https:\/\/tbenews.com\/tbe\/13-24-9\/","name":"Norway - 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