Meta-transcriptomic profiling of Ixodes ricinus and Ixodes persulcatus ticks from Finland reveals diverse RNA viromes, community structuring, and emerging viral lineages

Tick-borne viruses (TBVs) are a threat to human and animal health in northern Europe, where Ixodes ricinus and Ixodes persulcatus are undergoing range expansion. In Finland, the genetic diversity, population structure, and tick-associated RNA virome of these species remain insufficiently characterized. Characterizing tick-borne viruses in Finland is essential to detect emerging pathogens at the northern edge of tick expansion, where climate-driven ecological change may facilitate the spread of novel viruses with potential risks to human and animal health. We applied single-tick metatranscriptomic approach to profile and compare the RNA viromes of 92 adult I. ricinus and I. persulcatus collected from two locations in Finland. We identified 49 RNA viruses spanning 12 families, with Nairoviridae, Phenuiviridae, Partitiviridae, Flaviviridae, and Rhabdoviridae being the most represented. Viral community composition differed significantly between tick species, with I. persulcatus exhibiting more constrained but bunyaviridae-dominated viromes, whereas I. ricinus showed greater inter-individual variability and enrichment of partiti-like and iflavirus taxa. Phylogenetic reconstruction of conserved viral proteins supported the presence of several divergent viral lineages and confirmed first detection of multiple Eurasian tick-associated viruses in Finland, including Nuomin virus, Gakugsa tick virus, and Onega tick phlebovirus. Several detected viruses clustered within clades that include known or suspected zoonotic agents, highlighting the need for close monitoring of tick populations, especially in zones of sympatric occurrence where hybridization and associated close contact between the tick species has been observed. These findings reveal substantial, species-structured viral diversity in Finnish Ixodes ticks.