# Interrelation of the spatial and genetic structure of tick‐borne encephalitis virus, its reservoir host (Myodes glareolus), and its vector (Ixodes ricinus) in a natural focus area

## TL;DR

This study explores how the genetics of ticks, rodents, and the tick-borne encephalitis virus interact in natural areas where the virus is maintained.

## Contribution

The study reveals that rodent genetics, not tick genetics, significantly influence the long-term maintenance of tick-borne encephalitis virus foci.

## Key findings

- Bank voles in long-term TBEV foci have unique genetic structures that influence virus maintenance.
- Ticks show a panmictic genetic structure, suggesting no significant role in sustaining TBEV foci.
- Landscape genetics suggest no physical barriers explain the genetic structure of bank voles.

## Abstract

Tick‐borne encephalitis (TBE) virus is considered the medically most important arthropod‐borne virus in Europe. Although TBE is endemic throughout central Europe, ticks and rodents determine its maintenance in small, difficult‐to‐assess, natural foci. We investigated the interrelation between the population genetics of the main TBE virus (TBEV) vector tick (Ixodes ricinus), the most important reservoir host (Myodes glareolus, syn. Clethrionomys glareolus), and TBEV. Rodents and ticks were sampled on 15 sites within an exploratory study area, which has been screened regularly for TBEV occurrence in ticks for more than 10 years. On all 15 sites, ticks and bank voles were sampled, screened for TBEV presence via serology and RT‐PCR, and genetically examined. Moreover, TBEV isolates derived from these analyses were sequenced. In long‐term TBEV foci bank vole populations show extraordinary genetic constitutions, leading to a particular population structure, whereas ticks revealed a panmictic genetic structure overall sampling sites. Landscape genetics and habitat connectivity modeling (analysis of isolation by resistance) showed no landscape‐related barriers explaining the genetic structure of the bank vole populations. The results suggest that bank voles do not simply serve as TBEV reservoirs, but their genetic composition appears to have a significant influence on establishing and maintaining long‐term natural TBEV foci, whereas the genetic structure of TBEV's main vector I. ricinus does not play an important role in the sustainability of long‐term TBEV foci. A thorough investigation of how and to which extent TBEV and M. glareolus genetics are associated is needed to further unravel the underlying mechanisms.

Tick‐borne encephalitis is endemic throughout central Europe, ticks and rodents determine its maintenance in small, difficult‐to‐assess, natural foci. In long‐term TBEV foci bank vole populations show extraordinary genetic constitutions, leading to a particular population structure, whereas ticks revealed a panmictic genetic structure over all sampling sites. The results suggest that bank voles do not simply serve as TBEV reservoirs, but their genetic composition has a significant influence on establishing and maintaining long‐term natural TBEV foci, whereas the genetic structure of TBEV's main vector Ixodes ricinus does not play an important role in the sustainability of long‐term TBEV foci.