There are over 100 species of papillomavirus recognised,[9] though the ICTV officially recognizes a smaller number, categorized into 53 genera, as of 2019.[10][11][12] All 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.