Traditionally, virus taxonomy relied on phenotypic properties; however, a sequence-based virus taxonomy has become essential since the recent requirement of a species to exhibit monophyly. The species Cowpox virus has failed to meet this requirement, necessitating a reexamination of this species. Here, we report the genomic sequences of nine Cowpox viruses and, by combining them with the available data of 37 additional genomes, confirm polyphyly of Cowpox viruses and find statistical support based on genetic data for more than a dozen species. These results are discussed in light of the current International Committee on Taxonomy of Viruses species definition, as well as immediate and future implications for poxvirus taxonomic classification schemes. Data support the recognition of five monophyletic clades of Cowpox viruses as valid species.
