The 20th meeting of the executive committee of the international committee on virus taxonomy
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The 20th meeting of the executive committee of the international committee on virus taxonomy Virus species, higher taxa, a Universal Virus Database, and other matters The Executive Committee of the International Committee on Taxonomy of Viruses (ICTV), comprising four office-bearers, six Sub-committee chairmen and eight other members, normally meets once in the interval between Virology Congresses to consider taxonomic proposals coming from 39 Study Groups covering the whole of virology, and to prepare these proposals for presentation of the full ICTV which assembles every three years concurrently with the International Virology Congresses. The 20th meeting of' the Executive Committee of the ICTV was held at the Centers for Disease Control, Atlanta, Georgia, U.S.A. from 22nd to 24th April 1991. This meeting differed from the normal pattern of midterm meetings in that it was convened for the specific purpose of considering in depth some of the broader aspects of viral taxonomy, and several coopted guest speakers were invited to lead the discussion. The topics discussed were "The Issue of Higher Taxa", "The Species Concept in Virology", and "The Establishment of a Universal Virus Database". These topics will be the subject of more detailed articles in subsequent editions of VIROLO~'Z D]vJsloN N~ws, and only a brief summary of the proceedings is presented here. Perhaps the most significant outcome of the meeting was the acceptance of virus species as an entity in virus taxonomy, and the adoption of a new definition of virus species put forward by Marc Van Regenmortel. Definitions of virus species based on biological (gene pools), ecological (niches), evolutionary (lineages), or phenetic (morphology) criteria were considered and rejected. The concept of the polythetic species, on the other hand, found general favour since it can accomodate the inherent variability of viruses and it does not depend on tlhe existence of a unique diagnostic feature. A polythetic class is distinguished from an ordinary class in that members of the former need not have any single property in common. Each member of a polythetic class is defined by more than one property, and no single property is necessary or sufficient for membership of a polythetic class. The strength of the polythetic species concept is that it does not depend on strict definition of boundaries, and the following definition of virus species was adopted: "A virus species is a polythetic class of viruses that constitutes a replicating lineage and occupies a particular ecological niche." The chairmen of the Sub-committees now have the responsibility of implementing this decision with the assistance of a guidance document from the Executive Committee, and of coordinating the activities of their Study Groups in this task. The chairmen of the Study Groups will be required to produce working definitions for delineation of species within existing families or virus groups, and to establish the criteria for differentiating species and strains. The polythetic species concept implies
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