Geographical distribution and prevalence of tick‐borne encephalitis virus in questing Ixodes ricinus ticks and phylogeographic structure of the Ixodes ricinus vector in Norway

Abstract

The tick-borne encephalitis virus (TBEV), a zoonotic flaviviral infection, is endemic in large parts of Norway and Eurasia. Humans are mainly infected with TBEV via bites from infected ticks. In Norway, the main geographical distribution of ticks is along the Norwegian coastline from southeast (~59°N) and up to the southern parts of Nordland County (~65°N). In this study, we collected ticks by flagging along the coast from Østfold County to Nordland County. By whole-genome sequencing of the mitochondrial genome of Ixodes ricinus, the phylogenetic tree suggests that there is limited phylogeographic structure both in Norway and in Europe. The overall TBEV prevalence is 0.3% for nymphs and 4.3% for adults. The highest estimated TBEV prevalence in adult ticks was detected in Rogaland and Vestfold County, while for nymphs it is highest in Vestfold, Vest-Agder and Rogaland. The present work is one of the largest studies on distribution and prevalence of TBEV in ticks in Scandinavia, showing that the virus is wider distributed in Norway than previously anticipated. K E Y W O R D Sgeographical distribution, Ixodes ricinus, phylogeography, prevalence, TBEV, WGS | 371 VIKSE Et al.

Prevalence of tick‐borne encephalitis virus in questing Ixodes ricinus nymphs in southern Scandinavia and the possible influence of meteorological factors

“…in Viken County from the former counties of Østfold, Akershus and Vestfold (Vikse et al, 2020) and the present study reports higher TBEV EPP along the Oslofjord in Norway than previously detected.…”

“…In Southern Scandinavia, the spatial distribution of TBE cases does not fully coincide with the known distribution of TBEV in ticks. TBEV has been detected in ticks from coastal counties in Norway, from Viken in the southeast to Nordland in the north (Andreassen et al, 2012; Paulsen et al, 2015; Soleng et al, 2018; Vikse et al, 2020). However, all human TBE cases from Norway are reported from the southernmost parts of the country, specifically from the counties Agder, Vestfold and Telemark, and Viken (former Buskerud) (MSIS, 2022).…”

Low prevalence of tick-borne encephalitis virus antibodies in Norwegian blood donors

“…Vestfold and Telemark county is located in the southern part of Norway. TBEV is confirmed to be present in ticks collected along the coastline within the county, and seven of the 23 municipalities have reported at least one case of assumed locally acquired TBE [30,35]. However, the majority of cases are infected in the two neighbouring municipalities Porsgrunn and Larvik.…”

Tick-Borne Encephalitis Virus RNA Found in Frozen Goat’s Milk in a Family Outbreak

“…Due to climate change, TBE is causing increasing concern in Europe [ 1 , 9 , 10 ]. Over the last 30 years the endemic regions in Europe have expanded, covering many countries in central, northern and eastern Europe, with isolated cases reported from Sicily [ 11 ], the Netherlands [ 12 ] and Norway [ 13 , 14 ]. The number of reported human cases in Europe has increased by almost 400% in the last 30 years according to data of the European Centre for Disease Prevention and Control (ECDC; (accessed on 9 August 2022)) [ 10 ].…”