Metagenomic analysis of mosquitoes allows the genetic characterization of mosquito-associated viruses in different regions of the world. This study applied the metagenomic approach to search for novel viral sequences in seven species of mosquitoes collected from the Novosibirsk region of Western Siberia. Using NGS sequencing, we identified 15 coding-complete viral polyproteins (genomes) and 15 viral-like partial sequences in mosquitoes. The complete sequences for novel viruses or partial sequences of capsid proteins, hypothetical viral proteins, and RdRp were used to identify their taxonomy. The novel viral sequences were classified within the orders Tymovirales and Picornavirales, the families Partitiviridae, Totiviridae, Tombusviridae, Iflaviridae, Nodaviridae, Permutotetraviridae, Solemoviridae, with several attributed to four unclassified RNA-viruses. The main part of the novel putative viruses and viral sequences was associated with Coquillettidia richardii mosquito. This study is intended to increase our understanding of viral diversity in mosquitoes found in the natural habitats of Siberia, characterized by very long, snowy, and cold winters.

In this study, we investigated the features of co-infection with SARS-CoV-2 and nonpathogenic strain LEV8 of coxsackievirus A7 or enterovirus A71 for Vero E6 cells and Syrian hamsters. The investigation of co-infection with SARS-СoV-2 and LEV-8 or EV-A71 in the cell model was shown that a competitive inhibitory effect for these viruses were especially significant against SARS-CoV-2. Pre-infection with enteroviruses in animals caused more than a 100-fold decrease in the levels of SARS-CoV-2 virus replication in the respiratory tracts and more rapid clearance of the lower respiratory tract from infectious SARS-CoV-2. Co-infection with SARS-CoV-2 and LEV-8 or EV-A71 also reduced the severity of clinical manifestations of the SARS-CoV-2 infection for animals. Additionally, the histological data illustrated that co-infection with nonpathogenic coxsackievirus decreased the level of pathological changes by SARS-CoV-2 in the lungs. Research into the chemokine/cytokine profile demonstrated that the studied enteroviruses efficiently triggered this part of antiviral immune response, which can be associated with significant inhibition of SARS-CoV-2 infection. These results demonstrate that there exists a strong viral interference between the studied nonpathogenic strain of coxsackievirus A7 or enteroviruses A71 and SARS-CoV-2 pathogenic for humans in vitro and in vivo.