Introduction

Changes to virus taxonomy (the universal scheme of virus classification of the International Committee on Taxonomy of Viruses [ICTV]) take place annually and are the result of a multi-stage process. In accordance with the ICTV Statutes (http://ictv.global/statutes.asp), proposals submitted to the ICTV Executive Committee (EC) undergo a review process that involves input from the ICTV Study Groups (SGs) and Subcommittees (SCs), other interested virologists, and the EC. After final approval by the EC, proposals are presented for ratification to the full ICTV membership by publication on the ICTV website (http://ictv.global) followed by an electronic vote.

The latest set of proposals approved by the EC was made available on the ICTV website in February 2020 (see https://ictv.global/proposals-2019/ for all proposals combined into a single zip file, and use the links provided in the References to access individual proposals). A list of proposals was then emailed on February 19, 2020 to the 164 members of the ICTV, namely the EC Members, Life Members, ICTV Subcommittee Members including the SG Chairs, and ICTV National Representatives. Members were then requested to vote on whether to ratify the taxonomic proposals; voting closed on March 21, 2020.

Changes to virus taxonomy and to the Statutes of the International Committee for Taxonomy of Viruses

All proposals [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206] were ratified by ICTV members, in every case receiving an absolute majority of votes, between 55% and 62% of eligible voters. A summary of the taxonomy changes enacted by the proposals is provided in Table 1. Each proposal is cited and listed in the References to acknowledge the authors’ efforts and to provide links to the specific proposals on the ICTV website. These documents remain available for those who wish to see the full details of the proposals.

Table 1 Summary of taxonomic changes approved in March 2020
Full size table

A notable taxonomic change approved in this ratification is the extension of the realm Riboviria, a clade of viruses that use cognate RNA-directed RNA polymerases (RdRps) for their replication, to include also the reverse-transcribing viruses that use a homologous replication enzyme [6, 207,208,209,210]. In the current taxonomy, all available primary taxonomic ranks for this realm are filled. Three novel realms for distinct subsets of viruses with DNA genomes were established as well, i.e., Monodnaviria, comprising viruses of prokaryotes and eukaryotes with single-strand DNA genomes that utilize the rolling-circle replication mechanism and encode replication initiation endonucleases of the HUH superfamily; Varidnaviria, comprising viruses of prokaryotes and eukaryotes with double-strand DNA genomes and single vertical jelly-roll or double jelly-roll capsid proteins; and Duplodnaviria, comprising viruses of prokaryotes and eukaryotes with double-strand DNA genomes and HK97-fold capsid proteins [3,4,5]. A detailed justification for the establishment of these realms has been published recently [211].

To ensure that the ICTV maintains the expertise and flexibility needed to meet the challenges of virus taxonomy in the future, and to clarify the procedures for electing the Executive Committee, a working group established by the Executive Committee of the ICTV has proposed amendments to the ICTV Statutes. The amended Statutes were also ratified in the ICTV-wide vote and then approved in April 2020 by the Virology Division of the International Union of Microbiological Societies, which is the parent organization of the ICTV. The new Statutes can be found at https://ictv.global/statutes.asp. The key effects of adopting the new Statutes include: enlargement of the Executive Committee from 19 to 23 Members representing the diversity of virologists in geography, demography and expertise; establishment of a single nomination procedure and timeframe for all positions on the Executive Committee except Virus Subcommittee Chairs; and increased participation by ICTV Members in elections to the EC by allowing ballots other than those cast in person at the Plenary Meeting.

Conclusion

All proposals submitted for ratification were ratified by an absolute majority of the ICTV, and the changes proposed are now part of official ICTV taxonomy. New ICTV Statutes are now in force as well. An up-to-date list of all approved taxa can be found on the ICTV online website: https://ictv.global/msl/.