A broader definition of 'the virus species'.

We propose that the formal definition of a virus species by the International Committee on Taxonomy of Viruses (ICTV) should be broadened by removing the restrictive word "polythetic" from the current definition, so that any characters can be used to define species. This change will bring the definition of virus species into line with the species definitions of cellular organisms and broaden the range of characters available for describing virus species.