title: Prevalence and phylogenetic analysis of tick-borne encephalitis virus (TBEV) in field-collected ticks (Ixodes ricinus) in southern Switzerland.
abstract: BACKGROUND
  Tick-borne encephalitis is the most common tick-borne viral infection in Europe with 3,000 human cases reported each year. In Western Europe, the castor bean tick, Ixodes ricinus, is the principal vector of the tick-borne encephalitis virus (TBEV). TBEV appears to be spreading geographically and was recently detected for the first time in Canton Valais in the southern part of Switzerland. The purpose of the present study was to survey the I. ricinus tick populations of Canton Valais for TBEV.
  
  
  METHODS
  We collected a total of 19,331 I. ricinus ticks at 45 different sites in Canton Valais between 2010 and 2013. Ticks were processed in pools and tested for TBEV using reverse transcription quantitative PCR. The NS5 gene and the envelope gene of the TBEV isolates were partially sequenced for phylogenetic analysis.
  
  
  RESULTS
  TBEV was detected in tick populations at six of the 45 sites. These six sites were all located in a 33 km transect along the Rhône River. TBEV was detected in two sites for three of the four years of the study showing the temporal persistence of the pathogen. Prevalence of TBEV in the six positive sites ranged from 0.16% to 11.11%. Phylogenetic analysis found that all TBEV isolates from Canton Valais belonged to the European subtype. Genetic analysis found two distinct lineages of TBEV suggesting that Canton Valais experienced two independent colonization events.
  
  
  CONCLUSIONS
  TBEV appears to be well established at certain locations in Canton Valais.
authors.affiliation: Central Institute of Valais Hospitals, Infectious diseases, Av Grand Champsec 86, Sion, Switzerland. nadia.rieille@unine.ch.
authors.forename: Nadia
authors.initials: N
authors.lastname: Rieille
authors.forename: Stéphane
authors.initials: S
authors.lastname: Bressanelli
authors.forename: Caio C M
authors.initials: CC
authors.lastname: Freire
authors.forename: Séverine
authors.initials: S
authors.lastname: Arcioni
authors.forename: Lise
authors.initials: L
authors.lastname: Gern
authors.forename: Olivier
authors.initials: O
authors.lastname: Péter
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Voordouw
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA; D004669:Encephalitis Viruses, Tick-Borne / Q000235:genetics*; D015967:Gene Expression Regulation, Viral / Q000502:physiology; D014644:Genetic Variation; D018884:Ixodes / Q000821:virology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D011487:Protein Conformation; D013557:Switzerland; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D014759:Viral Envelope Proteins; D004247:DNA