Genome Diversity and Evolution of Papillomaviruses

Papillomaviruses are small DNA viruses that infect cutaneous and mucosal epithelia of humans, other mammals, and of at least some birds. Due to their important role in human neoplastic disease, a huge nucleotide sequence database with hundreds of complete or partial genome sequences has become established. The analysis of these sequences led to the notion that papillomaviruses genomes evolve very slowly, and nucleotide changes accumulate at a rate of about 1% per 100000 years, only slightly faster than the genomic changes of the hosts. The viruses form clades restricted to specific host species, although ancient diversification also gave rise to remotely related clades within individual host species. As phylogenetic trees of mammalian and bird papillomaviruses have semblance to phylogenetic trees of the infected animal species, host-linked evolution suggests that the papillomavirus genome organization is at least as old as the phylogeny of mammals and birds themselves, i.e. about 150 million years. While papillomaviruses are thought to be unrelated to other DNA viruses, a major homology between replication initiation proteins points to a common ancestor that papillomaviruses share with several other viruses and virus-like elements. The mechanisms of papillomavirus evolution are still largely unclear due to the very similar genetic composition and biology of all papillomaviruses.