The host spectrum of viruses is quite diverse, as they can sustainedly infect a few species to several phyla. When confronted with a new host, a virus may even infect it and transmit sustainably in this new host, a process called ‘viral spillover’. However, the risk of such events is difficult to quantify. As climate change is rapidly transforming environments, it is becoming critical to quantify the potential for spillovers. To address this issue, we resorted to a metagenomics approach and focused on two environments, soil and lake sediments from Lake Hazen, the largest High Arctic freshwater lake in the world. We used DNA and RNA sequencing to reconstruct the lake’s virosphere in both its sediments and soils, as well as its range of eukaryotic hosts. We then estimated the spillover risk by measuring the congruence between the viral and the eukaryotic host phylogenetic trees, and show that spillover risk increases with runoff from glacier melt, a proxy for climate change. Should climate change also shift species range of potential viral vectors and reservoirs northwards, the High Arctic could become fertile ground for emerging pandemics.

While many viruses have a single natural host, host restriction can be incomplete, hereby leading to spillovers to other host species, potentially causing significant diseases as it is the case with the Influenza A, Ebola, or the SARS-CoV-2 viruses. However, such spillover risks are difficult to quantify. As climate change is rapidly transforming environments, it is becoming critical to quantify the potential for spillovers, in an unbiased manner. For this, we resorted to a metagenomics approach, and focused on two environments in the High Arctic, soil and lake sediments from Lake Hazen. We used DNA and RNA sequencing to reconstruct the lake's virosphere and its range of eukaryotic hosts, and show that spillover risk is higher in lake sediments than in soil and increased with runoff from glacier melt - a proxy for climate change. Should climate change also shift species range of potential vectors northwards, the High Arctic could become fertile ground for emerging pandemics.