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Papillomaviridae is an ancient taxonomic family of non-enveloped DNA viruses, collectively known as ''papillomaviruses''. Several hundred species of papillomaviruses, traditionally referred to as "types", have been identified infecting all carefully inspected mammals,〔 but also other amniotes such as birds, snakes and turtles. Infection by most papillomavirus types, depending on the type, is either asymptomatic (e.g. most Beta-PVs) or causes small benign tumors, known as papillomas or warts (e.g. human papillomavirus1, HPV6 or HPV11). Papillomas caused by some types, however, such as human papillomaviruses 16 and 18, carry a risk of becoming cancerous. Papillomaviruses are usually considered as highly host- and tissue-tropic, and are thought to rarely be transmitted between species. Papillomaviruses replicate exclusively in the basal layer of the body surface tissues. All known papillomavirus types infect a particular body surface,〔 typically the skin or mucosal epithelium of the genitals, anus, mouth, or airways. For example, human papillomavirus (HPV) type 1 tends to infect the soles of the feet, and HPV type 2 the palms of the hands, where they may cause warts. Additionally, there are descriptions of the presence papillomavirus DNA in the blood and in the peripheral blood mononuclear cells. Papillomaviruses were first identified in the early 20th century, when it was shown that skin warts, or papillomas, could be transmitted between individuals by a filterable infectious agent. In 1935 Francis Peyton Rous, who had previously demonstrated the existence of a cancer-causing sarcoma virus in chickens, went on to show that a papillomavirus could cause skin cancer in infected rabbits. This was the first demonstration that a virus could cause cancer in mammals. ==Taxonomy of papillomaviruses== There are over 100 species of papilomavirus recognised,〔Kocjan BJ, Hosnjak L, Seme K, Poljak M (2013) Complete genome sequence of a novel human betapapillomavirus, HPV-159. Genome Announc. 2013 May 30;1(3). pii: e00298-13. doi: 10.1128/genomeA.00298-13.〕 though the ICTV officially recognizes 95 of them, arranged into 39 genera.〔(【引用サイトリンク】title=Virus Taxonomy: 2014 Release )〕 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. 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 30 genera.〔Bernard HU, Burk RD, Chen Z, van Doorslaer K, Hausen Hz, de Villiers EM (2012) Classification of papillomaviruses (PVs) based on 189 PV types and proposal of taxonomic amendments. Virology 401(1):70-79〕 This classification may need revision in the light of the existence of papilloma-polyoma virus recombinants.〔Rector A, Van Ranst M (2013) Animal papillomaviruses. Virology 445(1-2):213-23. doi: 10.1016/j.virol.2013.05.007 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「papillomaviridae」の詳細全文を読む スポンサード リンク
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