Investigation of the tick-borne encephalitis virus in Norway

Abstract

Expansion of the range of Ixodes ricinus ticks further north and to higher altitudes affects the spread of tick-borne encephalitis virus (TBEV) in new territories and increases the risk of human infections. Over the past decade, the number of tick-borne encephalitis (TBE) cases has increased in Norway and parts of the southern coast have been established as endemic. The aims of this study were to confirm the existence of TBEV endemic foci, determine the spread of TBE in different localities of Norway, review and compare relevant published records on the prevalence of TBEV in the different developmental stages and sex of the ticks. Ticks were collected from nine locations along the southern coast of Norway during June-July 2009. For the detection of TBEV-specific RNA, a real-time RT-PCR targeting a part of the 3’ non-coding region of the TBEV genome was used. A total of 1542 ticks grouped in 250 pools were examined and TBEV RNA was detected in 5 pools with overall prevalence of 0.32%.

Tick-Borne Encephalitis Virus: An Emerging Ancient Zoonosis?

“…Similarly, in the Krasnoyarsk region, an expansion of the tick area to the north was reported [28]. The increasing incidence of TBE was also observed in Poland [31], Norway [32], Sweden [33], Finland [34], and Mongolia [35]. In Central Europe [36], and in Italy [37], TBEV area was expanding to areas with higher elevation above sea level, which was also attributed to the warming climate.…”

New tick-borne encephalitis virus hot spot in Northern Zealand, Denmark, October 2019

“…Subsequent collection of I. ricinus ticks from a part of Tisvilde Hegn surrounding a well-visited forest playground, where Case 3 recalled a tick bite, identified a specific area adjacent to the playground to be an acute, new, high-risk TBEV micro-focus in Northern Zealand. The estimated high prevalence of TBEV is 8% at the centre of the focus which exceeds recent prevalence estimates of 0.6% from endemic Bornholm, as well as Denmark’s neighbouring countries and most European countries [4,5,8,10,11,13,15]. The presence of the virus in nymphs, but not adult ticks, and the molecular evolutionary analyses of the homogeneous TBEV sequences suggests a single TBEV introduction in 2019, probably by migrating birds from Norway.…”

“…The incidence of TBE has been increasing in Denmark, in its neighbouring countries as well and in the rest of Europe in recent years, which mirrors the increased abundance of ticks, the increased geographic spread and potentially climate changes [8-11]. The vector for the European virus subtype, TBEV-Eu, is Ixodes ricinus , which is prevalent in most of Europe and the dominant tick species in Denmark (> 90%) [12].…”

Field samplings of Ixodes ricinus ticks from a tick-borne encephalitis virus micro-focus in Northern Zealand, Denmark

“…Even though the micro-focus may have been temporary, continued surveillance of the site will be performed and TBE should still be considered in Denmark outside Bornholm if clinically relevant symptoms are present. There are indications that TBEVs geographical range is increasing in Sweden, Norway and Denmark (Jaenson et al, 2012;Sidorenko et al, 2018;Andersen et al, 2019). It is thus important to be aware of the establishment of new micro-foci in Denmark outside Bornholm.…”

“…TBE is a growing public health concern in Europe and the overall notification rate in EU/EEA rose from 0.4 cases per 100,000 population in 2015 to 0.6 cases per 100,000 population in 2016 (European Centre for Disease Prevention and Control (2018)). The incidence and geographical range of TBE is similarly increasing in Scandinavia (Jaenson et al, 2012;Sidorenko et al, 2018). In Denmark, TBE has been reported since the 1950s only from the Bornholm Island east of mainland Denmark in the Baltic Sea with an incidence of 3.8 cases per 100,000 persons per year (Ocias et al, 2017;Fomsgaard, 2018).…”