Abstract
RNA viruses are abundant infectious agents and present in all domains of life. Arthropods, including ticks, are well known as vectors of many viruses of concern for human and animal health. Despite their obvious importance, the extent and structure of viral diversity in ticks is still poorly understood, particularly in Europe. Using a bulk RNA-sequencing approach that captures the complete transcriptome, we analysed the virome of the most common tick in Europe – Ixodes ricinus. In total, RNA sequencing was performed on six libraries consisting of 33 I. ricinus nymphs and adults sampled in Norway. Despite the small number of animals surveyed, our virus identification pipeline revealed nine diverse and novel viral species, phylogenetically positioned within four different viral groups – bunyaviruses, luteoviruses, mononegavirales and partitiviruses – and sometimes characterized by extensive genetic diversity including a potentially novel genus of bunyaviruses. This work sheds new light on the virus diversity in I. ricinus, expands our knowledge of potential host/vector-associations and tick-transmitted viruses within several viral groups, and pushes the latitudinal limit where it is likely to find tick-associated viruses. Notably, our phylogenetic analysis revealed the presence of tick-specific virus clades that span multiple continents, highlighting the role of ticks as important virus reservoirs.
Highlights
Viruses are present in all domains of life[1, 2]
It was previously demonstrated that phlebo- and nairoviruses are present in I. ricinus ticks sampled in France[17]
These two viruses were the most common viruses found in the data set analysed here: Norway nairovirus 1 was present in five of the six libraries and Norway phlebovirus 1 was present in all six libraries, both of which were abundant within the tick libraries, with relative frequencies of viral contigs ranging between 0.02–0.47%, and with mean sequence depths ranging from to ×105−x8,492
Summary
Far less is known about the biodiversity of viruses present in ixodid ticks in the absence of an association with a specific vertebrate disease To address this question we performed high-throughput RNA sequencing on I. ricinus ticks collected predominantly in southern Norway (Fig. 1). Norway nairovirus 1 was most closely related to South Bay virus while the closest relative of Norway phlebovirus 1 was Blacklegged tick phlebovirus 1, both of which were described in Ixodes scapularis ticks collected in North America[7] These two viruses were the most common viruses found in the data set analysed here: Norway nairovirus 1 was present in five of the six libraries and Norway phlebovirus 1 was present in all six libraries, both of which were abundant within the tick libraries, with relative frequencies of viral contigs ranging between 0.02–0.47%, and with mean sequence depths ranging from to ×105−x8,492
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