Metaviromic analysis of Ixodes ticks in Northwestern Russia reveals high viral diversity and novel RNA virus lineages.

Ticks of the genus Ixodes are recognized as important vectors of a wide range of viral pathogens with potential implications for public and veterinary health. Recent advances in metagenomic sequencing have uncovered an unprecedented diversity within tick-associated viromes, yet much of the global tick metavirome remains unexplored, particularly in vast and ecologically diverse regions such as Northwestern Russia. In this study, we present a comprehensive metaviromic and phylogenetic characterization of viruses detected in Ixodes persulcatus and Ixodes ricinus ticks collected from five regions in Northwestern Russia between 2021 and 2023. Using high-throughput RNA sequencing, we identified viral sequences representing families Nairoviridae, Partitiviridae, Phenuiviridae, Flaviviridae, Chuviridae, and Narnaviridae, Orthototiviridae. Putative novel viral lineages were identified. Phylogenetic analyses revealed strong geographic structuring of some viral lineages. This suggests either the presence of local genotypes, or underrepresentation of Eurasian tick-associated viromes, in current databases. In addition to TBEV, other viruses previously associated with human illness were detected in ticks in Northwestern Russia (Beiji nairovirus, Mukawa virus). Our findings provide the first high-resolution snapshot of the tick virome in Northwestern Russia. They emphasize the importance of continued viral surveillance in underrepresented biogeographic zones. These data contribute to the growing global virome map and may inform the development of region-specific vector-borne disease countermeasures.