ICTV Master Species List (MSL)

The Master Species List (MSL) provides access to the official, current virus taxonomy approved by the ICTV. A new MSL will be uploaded whenever a new, revised taxonomy is ratified by the ICTV membership. These Master Species Lists (MSL) provide the complete ICTV taxonomy as a downloadable spreadsheet. MSL files are available for each release of the virus taxonomy since 2008. Classification of viruses is based on the collection and comparison of various characters that describe the virus, and can then be used to distinguish one virus from another. Characters can consist of any property or feature of the virus, and include the molecular composition of the genome; the structure of the virus capsid and whether or not it is enveloped; the gene expression program used to produce virus proteins; host range; pathogenicity; and sequence similarity. While all characters are important in determining taxonomic relationships, sequence comparisons using both pairwise sequence similarity and phylogenetic relationships have become one of the primary sets of characters used to define and distinguish virus taxa. Based on an assessment of characters, a hierarchical relationship is established that groups together viruses with similar properties. The properties that define higher-level taxa are shared with all lower-level taxa that belong to higher-level taxa. For example, viruses of the order Picornavirales are all non-enveloped, icosahedral particles containing one or two segments of positive-sense RNA. The family Picornaviridae is one of several families belonging to the order Picornavirales. Members of the family Picornaviridae contain a single monocistronic genome with conserved genome organization (arrangement of encoded polypeptides). Members of the genus Enterovirus (family Picornaviridae) share more than 42% amino acid identity across the length of their polyprotein. Finally, members of the species Enterovirus C, share a limited range of hosts and host receptors, have similar polyprotein processing programs, and share more than 70% amino acid identity in the polyprotein. Once these criteria for grouping similar viruses into common taxa are established, they are used as demarcation criteria to determine if newly discovered viruses are members of an existing species (and therefore also in existing higher-level taxa), or if the new viruses warrant creation of a new species (and potentially new higher-level taxa), if their properties are sufficiently distinct from the viruses in an existing species. The first internationally organized attempts to introduce order into the bewildering variety of viruses took place at the International Congress of Microbiology held in Moscow in 1966. A committee was created, later called the International Committee on Taxonomy of Viruses (ICTV), and was given the task of developing a single, universal taxonomic scheme for all the viruses infecting animals (vertebrates, invertebrates and protozoa), plants (higher plants and algae), fungi, bacteria and archaea. The ICTV was created as a committee of the Virology Division of the International Union of Microbiological Societies (IUMS) and is governed by Statutes approved by the Virology Division. The Statutes define the objectives of ICTV: (i) to develop an internationally agreed taxonomy for viruses (the term “viruses” for this purpose is taken to include viroids and some important groups of satellite viruses); (ii) to develop internationally agreed names for these taxa; (iii) to communicate taxonomic decisions to the international community of virologists; and (iv) to maintain an index of virus names. The Statutes also state that classification and nomenclature of viruses will be subject to rules set out in an International Code. Virus taxonomy differs from other types of biological classification because the ICTV not only regulates a Code of Nomenclature but also considers and approves the creation of virus taxa. Priority of publication is not the determining factor. The ICTV Executive Committee (EC) has established over 100 international Study Groups (SGs) covering all virus taxa. The Chair of each SG is appointed by the relevant Subcommittee Chair, who is a member of the EC. Each subcommittee is responsible for classes of viruses with different genome configurations infecting different hosts. The current subcommittees encompass Archaeal Viruses, Animal DNA Viruses and Retroviruses, Animal dsRNA and ssRNA- Viruses, Animal ssRNA+ Viruses, Bacterial Viruses, Fungal and Protist Viruses, and Plant Viruses. SG Chairs are responsible for (i) organizing discussions among SG members of emerging taxonomic issues in their field, (ii) overseeing the submission of proposals for new taxonomy, and (iii) preparing or revising relevant chapter(s) in ICTV Reports. The ICTV welcomes taxonomic proposals from any interested individual, although in practice, most are prepared by the relevant SG. A proposal template and guidance notes are available for downloading from https://ictv.global/taxonomy/templates. Proposals will be forwarded to the relevant SG and will also be made available on the ICTV website for public comment. Authors are then invited to respond to any comments made. Subcommittee Chairs then present taxonomic proposals to the EC for discussion and approval at the annual EC meeting. Straightforward proposals, such as those to create new species within existing genera for which species demarcation have been previously established, can normally be approved at a single meeting. More complex or controversial proposals are made available on the ICTV website for public comment before being re-considered by the EC. Proposals approved by the EC do not become accepted taxonomy until they have been ratified by the full ICTV membership. As specified in the Statutes, this includes members of the various Subcommittees (mostly SG Chairs), National Members and Life Members. Lists of members are provided at https://ictv.global/members. Ratification proceeds by an email vote, after which the approved taxonomy is updated at https://ictv.global/taxonomy/. In general, new taxonomy approved by the EC in the summer, is ratified by ICTV Members in March-April of the next year, at which time it becomes official. This site should always be consulted for the most up-to-date ICTV taxonomic information. Summaries of the voting decisions are also prepared and published annually in an article in Archives of Virology within the Virology Division News section, and approved taxonomic proposals are available from the ICTV web site.

主物种列表（Master Species List，MSL）可获取由国际病毒分类委员会（International Committee on Taxonomy of Viruses, ICTV）批准的官方现行病毒分类系统。每当ICTV全体成员表决通过新的修订版分类系统时，便会上传新版MSL。所有MSL均提供完整的ICTV病毒分类系统，支持以可下载电子表格的形式获取；自2008年起，每一次病毒分类系统更新版本均配有对应的MSL文件。

病毒分类基于对描述病毒的各类分类性状的收集与比较，以此实现不同病毒间的区分。分类性状可涵盖病毒的任意属性或特征，具体包括基因组分子组成、病毒衣壳结构与是否具有包膜、用于合成病毒蛋白的基因表达程序、宿主范围、致病性以及序列相似性。尽管所有分类性状在确定分类亲缘关系时均具有重要价值，但基于两两序列相似性与系统发育关系的序列比对，已成为定义和区分病毒分类单元的核心性状之一。

基于对各类性状的评估，可构建层级化的分类关系，将具有相似属性的病毒归为一类。定义高级分类单元的属性，为隶属于该高级单元的所有低级分类单元所共有。例如，小RNA病毒目（Picornavirales）的所有病毒均为无包膜的二十面体颗粒，其基因组包含1或2条正链RNA片段。小RNA病毒科（Picornaviridae）是小RNA病毒目下的多个科之一；小RNA病毒科的成员病毒均拥有单个单顺反子基因组，且具有保守的基因组组织结构（即编码多肽的排列方式）。肠道病毒属（Enterovirus，隶属于小RNA病毒科）的成员病毒，其多聚蛋白全长的氨基酸序列一致性超过42%；而C型肠道病毒（Enterovirus C）的成员病毒，则共享有限的宿主与宿主受体范围，具有相似的多聚蛋白加工程序，且其多聚蛋白的氨基酸序列一致性超过70%。

一旦将相似病毒归为同一分类单元的标准得以确立，这些标准便会作为划分依据，用于判定新发现的病毒究竟属于现有物种（因此也隶属于对应的高级分类单元），还是因与现有物种的病毒属性差异显著，需要创建新的物种（乃至潜在的新高级分类单元）。

首次在全球范围内对纷繁复杂的病毒进行系统性分类的尝试，始于1966年在莫斯科举办的国际微生物学大会。大会成立了一个委员会，后更名为国际病毒分类委员会（ICTV），其任务是为所有感染动物（脊椎动物、无脊椎动物与原生动物）、植物（高等植物与藻类）、真菌、细菌及古菌的病毒制定一套统一的全球性分类体系。ICTV作为国际微生物学联合会（International Union of Microbiological Societies, IUMS）病毒学分会的委员会成立，并受该分会批准的章程约束。

该章程明确了ICTV的四项宗旨：（i）制定全球统一认可的病毒分类系统（本条款中"病毒"一词涵盖类病毒与部分重要的卫星病毒类群）；（ii）为这些分类单元制定全球统一认可的名称；（iii）向全球病毒学界通报分类学决议；（iv）维护病毒名称索引。章程同时规定，病毒的分类与命名需遵循《国际病毒分类与命名法规》中的相关规则。

病毒分类与其他生物分类方式不同，因为ICTV不仅负责监管命名法规，还需审议并批准病毒分类单元的设立，且发表优先级并非决定性因素。ICTV执行委员会（Executive Committee, EC）已设立100余个国际研究组（Study Groups, SGs），覆盖所有病毒分类单元。每个研究组的组长由相应的亚委员会主席任命，而亚委员会主席均为执行委员会成员。每个亚委员会负责管辖感染不同宿主、具有不同基因组结构的病毒类群；当前的亚委员会包括：古菌病毒、动物DNA病毒与逆转录病毒、动物双链RNA（dsRNA）及负链单链RNA（ssRNA-）病毒、动物正链单链RNA（ssRNA+）病毒、细菌病毒、真菌与原生生物病毒以及植物病毒。

研究组组长的职责包括：（i）组织研究组成员讨论其研究领域内新兴的分类学议题；（ii）监督新分类学提案的提交工作；（iii）编写或修订ICTV报告中的相关章节。ICTV欢迎所有感兴趣的个人提交分类学提案，但在实际操作中，多数提案由相应的研究组起草。提案模板与指南说明可从"https://ictv.global/taxonomy/templates"下载获取。提案将被提交至相应的研究组，同时也会在ICTV官网发布以征求公众意见；随后将邀请提案作者对收到的意见作出回应。亚委员会主席随后会在执行委员会年度会议上，将分类学提案提交至执行委员会进行讨论与表决。

简单直接的提案（如在已确立物种划分标准的现有属内创建新物种）通常可在单次会议上获得通过。更为复杂或存在争议的提案，则会先在ICTV官网发布并征求公众意见，之后再由执行委员会重新审议。经执行委员会批准的提案，需获得ICTV全体成员的表决通过，才能成为正式的分类系统。如章程所规定，ICTV全体成员包括各亚委员会成员（多数为研究组组长）、国家成员与终身成员。成员名单可在"https://ictv.global/members"查询。表决通过电子邮件投票进行，投票结束后，更新后的官方分类系统将发布于"https://ictv.global/taxonomy/"。通常情况下，执行委员会在夏季批准的新分类系统，会于次年3-4月由ICTV全体成员表决通过，正式成为官方分类系统。如需获取ICTV最新的分类学信息，请始终查阅该网站。

投票决议的年度总结会每年发表于《病毒学档案》（Archives of Virology）的病毒学分部新闻板块，而经批准的分类学提案可从ICTV官网获取。