Realm (virology)

While historically it was difficult to determine deep evolutionary relations between viruses, in the 21st century methods such as metagenomics and cryogenic electron microscopy have enabled such research to occur, which led to the establishment of Riboviria in 2018, three realms in 2019, and two in 2020.

[6] Duplodnaviria contains double-stranded DNA (dsDNA) viruses that encode a major capsid protein (MCP) that has the HK97 fold.

[11] Herpesviruses are known to cause a variety of epithelial diseases, including herpes simplex, chickenpox and shingles, and Kaposi's sarcoma.

[3] Eukaryotic monodnaviruses are associated with many diseases, and they include papillomaviruses and polyomaviruses, which cause many cancers,[15][16] and geminiviruses, which infect many economically important crops.

[6] Poxviruses have been highly prominent in the history of modern medicine, especially Variola virus, which caused smallpox.

[23] Many varidnaviruses are able to become endogenized, and a peculiar example of this are virophages, which confer protection for their hosts against giant viruses during infection.

[24] The realm currently includes viruses from three families, Lipothrixviridae, Rudiviridae, and Tristromaviridae, all infecting hyperthermophilic archaea.

[25][26] The MCPs of ligamenviral particles have a unique α-helical fold first found in the MCP of rudivirid Sulfolobus islandicus rod-shaped virus 2 (SIRV2).

[27] All members of the Adnaviria share a characteristic feature in that the interaction between the MCP dimer and the linear dsDNA genome maintains the DNA in the A form.

Additional common features include a rod-like structure and a RNA-binding "delta antigen" encoded in the genome.

[29] In two votes in 2018 and 2019, the ICTV agreed to adopt a 15-rank classification system for viruses, ranging from realm to species.