Prevalence of tick borne-encephalitis virus (TBEV) and phylogeographic structure of its vector Ixodes ricinus

Abstract

Ixodes ricinus is the most common vector in Europe and it is the primary vector for tick-borne encephalitis virus (TBEV) in Norway. Tick-borne encephalitis (TBE) cases have been reported yearly from Norway since the first case occurred in 1997. The aim of present study was to investigate the prevalence of TBEV and the phylogeographic structure of its vector I. ricinus ticks from several parts of Norway. A total of 1595 ticks were screened for TBEV from two sites of Southern Norway. This region is known for one of the highest number of TBE cases in the country. Ticks were collected by flagging in May and June 2015. A subpopulation of 1480 nymphs and 115 adult ticks were investigated for TBEV by real time polymerase chain reaction (PCR) amplification of the envelope gene. Positive samples from real-time PCR were confirmed by pyrosequencing. The estimated prevalence of TBEV was 0.41% and 2.17% among nymphs and adults from Vanse in Vest-Agder County and 0.69% and 1.4% among nymphs and adults from Bjønnes in Telemark County. A total of 33 ticks including 30 nymphs (pools of ten) and 3 adults was collected in 2014 from different parts of Norway. Complete mitochondrial genome of six samples (three pools of nymphs and 3 adults) successfully sequenced from Next generation sequencing (NGS). Six sequences from this study and 724 previously published mitochondrial DNA sequences were used for reconstruction of phylogenetic trees with Maximum likelihood (ML) and Bayesian method. The phylogenetic trees showed partial or lack of phylogeographic structure in Norwegian I. ricinus ticks. This study confirmed prevalence of TBEV from two sites in southern part of Norway and there was low or lack of phylogeographic structure in its vector I. ricinus.