Virologists align system to classify viruses with that of cellular organisms

28 April 2020• NEWSITEM

A group of virus experts representing the International Committee on Taxonomy of Viruses (ICTV) has announced a fundamental change to the way viruses are systematically classified. The transformed taxonomy system allows scientists to classify viruses in a hierarchical structure similar to that used for cellular organisms, like animals, bacteria and plants. The ICTV describes their decision and its implications in a Consensus Statement in the scientific journal Nature Microbiology.

A comparison of the ICTV taxonomic rank hierarchy in 1991–2017 and 2019. Taxonomic ranks are shown in relation to the distribution pattern of taxa. The number of taxa assigned to each rank (December 2019, MSL34) are shown in white font on the 15-rank structure. When the ranks are described as a hierarchy, the species rank is often referred to as the lowest rank and the realm rank as the highest rank. However, when the ranks are used as phylogenetic terms, the realm rank can be described as basal and the species rank as apical or terminal. Both conventions are used in this Consensus Statement. Black arrows, ranks common to the five- and 15-rank structure; pink arrows, ranks introduced in the 15-rank structure.A taxonomy is a way to group organisms in clusters based on their shared characteristics, and name and assign clusters to hierarchical ranks. After multi-year deliberations, the  structure of virus taxonomy is expanded by ten ranks added to the existing five-rank taxonomy. The majority of new ranks were introduced to reveal connections between distantly related viruses which were not considered in the taxonomy used over almost 30 years.

“This revolutionary advancement was prompted by the on-going massive virus discovery using next generation sequencing in metagenomics. It effectively recognizes viruses as part of our biosphere. Now viruses could be classified using principles established for cellular organisms by Carolus Linnaeus and Charles Darwin and employing methods of comparative genomics”, explains first author Alexander Gorbalenya, LUMC Professor Emeritus and past ICTV Vice-President.

Virus origins and evolution

The authors believe that the new structure of virus taxonomy will stimulate further research on virus origins and evolution and could promote crosstalk with the taxonomies of cellular organisms. Also, they illustrate how the new system will benefit medical community and public by comparing taxonomies of human Ebola virus, severe acute respiratory syndrome coronavirus and herpes simplex virus 1. “This comparison shows that these viruses, although all capable infecting humans, are vastly different taxonomically on biological grounds. For instance, the human Ebola virus and SARS-CoV are as much distant to each other as would humans and yeast in the taxonomy of cellular life forms”, according to Gorbalenya.

More information? Read the paper 'The new scope of virus taxonomy: partitioning the virosphere into 15 hierarchical ranks'  in Nature Microbiology.

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