Reinbold-Wasson et al.
Tick-borne encephalitis virus in Dermacentor reticulatus ticks, Poland. PeerJ. 2026;14:e21588. doi:10.7717/peerj.21588
In Europe, tick-borne encephalitis virus (TBEV) has historically been associated primarily with Ixodes ricinus. However, the vector competence of Dermacentor reticulatus for TBEV has also been experimentally confirmed, and TBEV-positive D. reticulatus ticks have been detected in several European countries, including Germany and Poland (see Snapshot week 25/2024).
A tick surveillance study was conducted at military training areas across three regions of northeastern Poland. I. ricinus and D. reticulatus ticks were collected by flagging across diverse habitats. TBEV was detected in one of 106 pools comprising a total of 418 D. reticulatus ticks. The TBEV-positive pool contained three adult D. reticulatus ticks. Subsequent sequencing recovered approximately 99% of the viral genome, producing the first full-length TBEV genome sequence obtained from this tick species. Phylogenetic analysis classified the virus as belonging to the European subtype and showed that it was most closely related to a 2019 Hungarian isolate identified nearly 1,000 km away.
The identification of the European TBEV subtype is consistent with previous findings from other parts of Poland. The close phylogenetic relationship between the Polish and Hungarian sequences may indicate viral migration or shared ancestry across a considerable geographical distance.
The geographical range of D. reticulatus has expanded in several European countries and increases in its distribution and local population density have been documented over recent decades (TBE Book, Chapter 5). Although I. ricinus remains the principal vector of TBEV in Europe, experimental and field evidence indicates that D. reticulatus can contribute to TBEV transmission and circulation in endemic foci. The findings of this study therefore reinforce the importance of continued tick and pathogen surveillance in TBEV-endemic regions such as Poland.