Our dating locates the tRE after LIV's colonization of the British Isles. Little is known about the modes of Tick-borne encephalitis virus dispersal over long distance. Birds on a longitudinal migrating route have been found to carry infected ticks through Scandinavia [59] . However, phylogenetic analyses have not shown any clear admixture of Northern and Southern strains that would point towards bird distribution. Therefore, livestock importation from central Europe to the UK seems a more likely explanation for the footprint of past W-TBEV presence observed in the LIV genome. It is not clear why W-TBEV strains did not form stable foci in the British Isles; possibly the number of continental strains was too small to find its way from infected sheep to the small rodents that are their natural vertebrate hosts.