Introduction

The International Committee on Taxonomy of Viruses (ICTV) is the body tasked by the International Union of Microbiological Societies (IUMS) to make decisions on matters of virus classification and nomenclature [1]. ICTV activities are governed by statutes (the Statutes) [2]. One of these Statutes states that classification and nomenclature will be subject to rules (the Rules) set out in an international code (the Code). The most recent version of this International Code of Virus Classification and Nomenclature (ICVCN) is available in the latest, 9th, ICTV Report, which was published in 2011 [3].

The ICVCN is organized in three major parts: Section 1 outlines the “Statutory basis for the International Committee on Taxonomy of Viruses (ICTV)”. Section 2 describes the “Principles of nomenclature”. Finally, section 3 outlines the “Rules of Classification and Nomenclature” [capitalization or lack thereof is identical to the headlines in the code] [3].

In contrast to the International Code of Zoological Nomenclature (ICZN Code; http://iczn.org), the International Code of Nomenclature of Bacteria (ICNB; http://www.ncbi.nlm.nih.gov/books/NBK8817/), and the International Code of Botanical Nomenclature (ICBN; http://ibot.sav.sk/icbn/main.htm), the ICVCN is rather short and still relatively imprecise. This article is the first of a series of manuscripts that outlines suggestions and proposals that would make the ICVCN a more precise instrument for virus taxonomy, while at the same time decreasing currently existing confusion among laboratory virologists regarding the use of the Rules put forth in the Code.

Proposal to delete Rule 3.41

ICVCN Rule 3.41 is the last Rule of the Code, located in Subsection IX (“Rules for Orthography”) of Section 3 (“Rules of Classification and Nomenclature”). It states

“In formal usage, the name of the taxon shall precede the term for the taxonomic unit”

and is followed by a comment that is not part of the official rule:

“Comments: For example, the correct formal descriptions of various taxa are … the family Herpesviridae, …the genus Morbillivirus, …. the genus Rhinovirus, …. the species Tobacco necrosis virus D, and so on”.

An official proposal (“TaxoProp”) to delete this Rule (TaxoProp No. 2012.001aG.U.v1.delete_Rule_3.41.pdf) was submitted on July 5, 2012, to the ICTV and provisionally approved (http://talk.ictvonline.org/files/proposals/taxonomy_proposals_general1/m/gen02/4333.aspx) for three reasons.

First, the Comment contradicts the Rule it is supposed to explain. The Rule states that the name of the taxon should precede the term for the taxonomic unit, but the comment suggests the opposite (Table 1).

Table 1 Usage of taxon names and taxonomic units
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Second, it is unnecessary in a set of taxonomic rules since it is purely stylistic. To the best of our knowledge, there is no difference in meaning between, for instance, “the Xyzviridae family”, “the family Xyzviridae” and “(the) Xyzviridae” (with Xyz being a placeholder for any ICTV-accepted family name). In fact, the term “family” in this context is redundant and therefore stylistically unpleasant because the formal suffix, -viridae, denotes family. The same is true at all taxonomic levels (Table 2). Formal taxon suffixes are widely accepted and well known among virologists. It is therefore self-evident that Xyzvirales refers to an order, Xyzviridae refers to a family, Xyzvirinae refers to a subfamily, Xyzvirinae refers to a genus and Xyz virus refers to a species.

Table 2 Taxon-specific suffixes accepted by the ICTV
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Third, the Rule is not observed in any consistent manner by the general virology community, including members of ICTV Study Groups and possibly even ICTV members. Sentence fragments such as “the Xyzvirales/Xyzviridae/Xyzvirinae/Xyzvirus/Xyz virus” (name of the taxonomic unit, “order/family/subfamily/genus/species,” is missing) and “the Xyzvirales/Xyzviridae/Xyzvirinae/Xyzvirus/Xyz virus order/family/subfamily/genus/species” and “the order/family/subfamily/genus/species Xyzvirales/Xyzviridae/Xyzvirinae/Xyzvirus/Xyz virus” are found in the published literature equally often. None of these three usages differ in information content from the others.

In conclusion, the deletion of Rule 3.41 will bring the Code into line with current practice without adversely affecting taxonomic precision. Deletion of the Rule is also straightforward, as other parts of the Code are not adversely affected by doing so. Since Rule 3.41 is the last Rule of the Code, its deletion would not require renumbering of other Rules and would only require deletion of a reference to it in the Comment to Rule 3.2 (“The universal virus classification system shall employ the hierarchical levels of Order, Family, Subfamily, Genus, and Species”). Once the Rule is deleted, numerous manuscripts will be retrospectively in compliance with the Code, and errors will be avoided prospectively.