Papillomaviridae - Taxonomy of Papillomaviruses

Taxonomy of Papillomaviruses

Papillomaviruses (PVs) have similar genomic organizations, and any pair of PVs contains at least five homologous genes, although the nucleotide sequence may diverge by more than 50%. Phylogenetic algorithms that permit the comparison of homologies led to phylogenetic trees that have a similar topology, independent of the gene analyzed. Phylogenetic studies strongly suggest that PVs normally evolve together with their mammalian and bird host species, do not change host species, do not recombine, and have maintained their basic genomic organization for a period exceeding 100 million years. These sequence comparisons have laid the foundation for a PV taxonomy, which is now officially recognized by the International Committee on Taxonomy of Viruses. All PVs form the family Papillomaviridae, which is distinct from the Polyomaviridae thus eliminating the term Papovaviridae. Major branches of the phylogenetic tree of PVs are considered genera, which are identified by Greek letters. Minor branches are considered species and unite PV types that are genomically distinct without exhibiting known biological differences. This new taxonomic system does not affect the traditional identification and characterization of PV "types" and their independent isolates with minor genomic differences, referred to as "subtypes" and "variants", all of which are taxa below the level of "species". The family Papillomaviridae currently contains at least 29 genera.