Global Riverine Viruses: Abundance, Diversity, Potential Health Threats, and Research Prospects

Rivers are important freshwater resources and the cradle of human civilization, while also being a core area of global biogeochemical cycles, possessing crucial ecological value. Viruses, as the most abundant biological entities in river ecosystems, significantly influence the biogeochemical cycling processes by infecting host organisms such as bacteria and algae. At the same time, rivers serve as important pathways for the transmission and spread of pathogenic viruses, posing potential threats to the biological safety of watersheds. However, current global understanding of the structure and diversity of river virus communities remains insufficient. Systematically analyzing the species composition and diversity of river viruses, revealing their key influencing factors, and clarifying their virus-host relationships are critically important for comprehensively understanding the ecosystem functions of aquatic viruses, assessing their potential health risks, and predicting their response patterns in the context of climate change. This study first systematically reviews research literature on viruses in rivers over the past thirty years (since 1989), covering six continents and 33 rivers, and comprehensively analyzes the core biogeochemical parameters that influence river virus communities. The findings indicate that the variation range of viral abundance in global river waters is generally between 105 to 108 VLPs/mL, bacterial abundance ranges from 105 to 107 Cells/mL, and the virus-to-bacteria ratio varies from 0.4 to 55.4. Statistical analysis shows that bacterial abundance, nitrogen content in various forms in the water, total phosphorus, and dissolved oxygen are the main factors affecting virus abundance. Additionally, this study delves into the species composition, host associations, and potential pathogenic risks of river viruses based on the river virus data from the global virus database IMG-VR4 (including 574,815 viral genome sequences). It finds that bacteriophages dominate river virus communities, accounting for 88% of the total number of analyzed river viral genomes. Notably, up to 9,626 related viral genome records from animals (including humans) were detected from freshwater environments, comprising 1.7% of the total viral genomes. Among these viruses, high-risk categories with potential pathogenicity include coronaviruses, herpesviruses, and human papillomaviruses. Finally, this paper projects future directions for river virus research, suggesting that future studies should focus on the following areas: (1) seasonal dynamics and interannual variations of viral abundance and community composition in river waters; (2) community characteristics, functions, and ecological roles of RNA viruses in river waters; (3) mechanisms by which global changes (such as climate warming and land-use changes) affect river virus community structure and function; (4) efficient monitoring technologies and prevention strategies for potential pathogenic viruses in rivers.