Molecular detection and characterization of tick-borne encephalitis virus in ixodid ticks in Lithuania

Tick-borne encephalitis (TBE), which is one of the most dangerous human infections, affects the central nervous system and can occur in people of all ages. During the last few decades the incidence of the disease has been increasing and it is a growing health problem in almost all European and Asian countries where it is endemic. Lithuania is one of the countries with the highest number of reported TBE cases, with an average of 450 cases of TBE reported yearly. The main vectors of the TBE virus (TBEV) in Euro-Asia region are ticks from the Ixodidae family, mainly Ixodes ricinus and Ixodes persulcatus. The aim of this study was to investigate the current prevalence of TBE virus in different species of ticks and genetically characterize the strains of virus distributed in Lithuania. In March-September 2017, 1,884 ticks were collected from eight Lithuanian counties in 18 regions. The collected ticks were identified as I. ricinus (n=1,351) and D. reticulatus (n=533). For RNA extraction, the ticks were grouped in 267 pools according to species, sampling site, development stage and sex. For the detection of TBEV, quantitative realtime reverse transcription-PCR (RT-PCR) was performed. Samples found positive by real-time PCR were used for one step RT-PCR and for nested PCR for future sequencing of the partial E protein and NS3 genes. The minimum infection rate (MIR) of TBEV in the analyzed ticks was 1.52% (8/524) (1.86% I. ricinus and 5.6% D. reticulatus). TBEV was detected in adult ticks. The TBEV prevalence in males and females of each species was not significantly different. The phylogenetic analysis of NS3 and E gene sequences showed that the detected strains belong to the European subtype and are specific to Lithuania. In addition, this is the first detection of TBEV in D. reticulatus ticks in LithuaniaBiologijos katedraVytauto Didžiojo universiteta