Abstract
This review provides a summary of the recently ratified changes to genus and species nomenclature within the virus family Flaviviridae along with reasons for these changes. First, it was considered that the vernacular terms “flaviviral”, “flavivirus”, and “flaviviruses” could under certain circumstances be ambiguous due to the same word stem “flavi” in the taxon names Flaviviridae and Flavivirus; these terms could either have referred to all viruses classified in the family Flaviviridae or only to viruses classified in the included genus Flavivirus. To remove this ambiguity, the genus name Flavivirus was changed to Orthoflavivirus by the International Committee on Taxonomy of Viruses (ICTV). Second, all species names in the family were changed to adhere to a newly ICTV-mandated binomial format (e.g., Orthoflavivirus zikaense, Hepacivirus hominis) similar to nomenclature conventions used for species elsewhere in biology. It is important to note, however, that virus names remain unchanged. Here we outline the revised taxonomy of the family Flaviviridae as approved by the ICTV in April 2023.
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Introduction
The family Flaviviridae encompasses four genera and 89 species [1]. The International Committee on Taxonomy of Viruses (ICTV) [5] recently made a number of changes to the names of genera and species in the family. This review describes these changes and the reasons for them. As a guide for those working in the flavivirus field, we also provide a comprehensive list of the previous and new nomenclature for each species and their viruses.
New genus name Orthoflavivirus
The genus Flavivirus within the family Flaviviridae was established for a large number of arthropod-borne viruses (e.g., dengue viruses and Zika virus) that are high-consequence human and veterinary pathogens [6]. The genus name Flavivirus contained the word stem “flavi”, which is also used for the family name. Therefore, the vernacular terms “flaviviral”, “flavivirus”, and “flaviviruses” were ambiguous, as these words might have referred to all members of the family (viruses of the genera Flavivirus, Hepacivirus, Pegivirus, and Pestivirus) or only to those of the genus Flavivirus.
To preclude this potential confusion, a taxonomic proposal (TaxoProp 2022.007S.A.Flaviviridae_1genren_sprenamed) was submitted to the ICTV in 2022. It proposed that the genus Flavivirus be renamed Orthoflavivirus, which roughly translates to “true flaviviruses” or “flaviviruses sensu stricto”. This proposal was approved by the ICTV Executive Committee in late 2022 and ratified by the ICTV in April 2023 [2, 9]. Consequently, the terms “flaviviral”, “flavivirus”, and “flaviviruses” should be used to refer to the collective members of the family Flaviviridae, whereas the terms “orthoflaviviral”, “orthoflavivirus”, and “orthoflaviviruses” should be used for viruses of the genus Orthoflavivirus (all orthoflaviviruses are flaviviruses, but not all flaviviruses are orthoflaviviruses).
Change to species names in the family Flaviviridae
In March 2021, the ICTV ratified TaxoProp 2018.001G.R.binomial_species, which requires all species names to follow a new codified rule:
"A species name shall consist of only two distinct word components separated by a space. The first word component shall begin with a capital letter and be identical in spelling to the name of the genus to which the species belongs. The second word component shall not contain any suffixes specific for taxa of higher ranks. The entire species name (both word components) shall be italicized" [3, 7].
The purpose of this rule is to differentiate more clearly the name of a virus from the name of the species (taxon) to which it is assigned by using the standardized genus + species epithet format found elsewhere in biological taxonomy nomenclature [8]. For orthoflaviviruses, this change was particularly relevant because most species names were the same as the virus names, apart from the orthography; e.g., yellow fever virus was a member of the species Yellow fever virus, a situation that created confusion.
The new binomial rule required all names of species previously included in the genus Flavivirus to adhere to the format “Orthoflavivirus xxxxxx”, in which “xxxxxx” represents a single word. At the same time, the opportunity was taken to abandon the single-letter species epithets used for names of species included in the genera Hepacivirus, Pegivirus, and Pestivirus and instead establish a consistent naming format within the family Flaviviridae. New species names were proposed according to guidance outlined by Postler et al. [4] in the same proposal that addressed the genus name issue (TaxoProp 2022.007S.A.Flaviviridae_1genren_sprenamed). Tables 1, 2, 3 and 4 list the current taxonomy of the family Flaviviridae, including the prior species names as a reference; Table 5 provides guidance for applying the updated nomenclature in manuscripts.
As with species-renaming proposals elsewhere in virus taxonomy, it should be stressed that these changes to the names of virus species have no influence on the names of the viruses classified within them. Thus, for instance, the virus name “Zika virus” and its abbreviation “ZIKV” remain unchanged even though the species, Zika virus, was renamed Orthoflavivirus zikaense. Similarly, hepatitis C virus (HCV) remains the same, whereas the species was renamed Hepacivirus hominis.
Conclusion
We hope this description of the modifications and replacements of genus and species names is of value by both explaining the reasons for the nomenclature changes and providing a useful reference list for those working in the field. The ICTV Online Report chapter on the family Flaviviridae has also been updated with the new genus and species names [6].
Data availability
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References
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International Committee on Taxonomy of Viruses (ICTV) (2023) Approved proposals. https://ictv.global/files/proposals/approved. Accessed 17 July 2023
International Committee on Taxonomy of Viruses (ICTV) (2023) ICTV Code. The International Code of Virus Classification and Nomenclature (ICVCN). March 2021. https://ictv.global/about/code. Accessed 17 July 2023
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Acknowledgements
We thank Anya Crane (NIH NIAID DCR IRF-Frederick) for critically editing the manuscript.
Funding
This work was supported in part through Laulima Government Solutions, LLC, prime Contract No. HHSN272201800013C with the U.S. National Institute of Allergy and Infectious Diseases (NIAID). J.H.K. performed this work as an employee of Tunnell Government Services (TGS), a subcontractor of Laulima Government Solutions, LLC, under Contract No. HHSN272201800013C. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Department of Health and Human Services or of the institutions and companies affiliated with the authors.
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Martin Beer, Bradley J. Blitvich, Jens Bukh, Xavier de Lamballerie, J. Felix Drexler, Allison Imrie, Amit Kapoor, Galina G. Karganova, Philippe Lemey, Volker Lohmann, Peter Simmonds, Donald B. Smith, Jack T. Stapleton: The members of the 2020–2023 International Committee on Taxonomy of Viruses (ICTV) Flaviviridae Study Group.
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Postler, T.S., Beer, M., Blitvich, B.J. et al. Renaming of the genus Flavivirus to Orthoflavivirus and extension of binomial species names within the family Flaviviridae. Arch Virol 168, 224 (2023). https://doi.org/10.1007/s00705-023-05835-1
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DOI: https://doi.org/10.1007/s00705-023-05835-1