Virus taxonomy and megataxonomy (Vira domain) – current status
L'vov Dk, V. G. Akimkin, Zaberezhnyĭ Ad, С. В. Борисевич, Sergey V. Alkhovsky
Abstract
For nearly 80 years since the discovery of the first virus by the Russian scientist D.I. Ivanovsky, it has been recognized that all organisms of Earth’s biosphere serve as natural hosts for viruses. Viruses, grouped within the informal domain Vira, infect all three domains of cellular life: archaea – Archaea, bacteria – Bacteria, and eukaryotes – Eucarya (algae, fungi, protozoa, plants, invertebrates, and vertebrates). The formation of viral population gene pools through interactions with the gene pools of their hosts has taken place under changing environmental conditions over 3.5 billion years, giving rise to the vast diversity of the virosphere. The accumulation of data on the Earth’s virosphere, facilitated by the advent of high-throughput sequencing technologies (NGS), has necessitated a reassessment of approaches to virus classification and, since 2018, has led to a reform of viral taxonomy through the introduction of higher taxonomic ranks (megataxonomy). As of September 2025, the International Committee on Taxonomy of Viruses (ICTV) recognizes 15 taxonomic ranks for viruses, the most significant being: realm – 7, kingdom – 11, phylum – 23, class – 49, order – 93, family – 368, genus – 3769, and species – 16,215. Ongoing advances in metagenomics, metatranscriptomics, and the global ecology of the virosphere will inevitably drive further changes in viral taxonomy and megataxonomy. These developments are of fundamental importance for understanding the evolution of the biosphere and of practical relevance for developing new strategies to strengthen biological security and to mitigate the consequences of epidemic emergencies associated with emerging and reemerging infections.