**2. Classification and carcinogenicity of HPVs**

Papillomaviruses are from the *Papillomaviridae* family and all HPV genotypes share a common structure, L1 protein, that is highly conserved and consequently used for taxonomical pur‐ poses[1]. HPVs are classified into 16 genuses (Alpha, Beta, etc.), which are also divided into species. Genus of *Papillomaviridae* share less than 60% nucleotide sequence identity in the L1 protein whereas species within a genus share between 60% and 70% nucleotide identity. A

© 2013 Laprise and Trottier; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

new HPV isolate is recognized as a new genotype when the nucleotide sequence of the L1 gene differs by more than 10% from the genotype with which it has the greatest homology in DNA sequence. More than 100 HPV genotypes have been identified in humans from which over 40 genotypes infect mucosa of anogenital tract and other mucosal areas. As anogenital HPV infections is the interest of this chapter, focus is made on alpha-papillomavirus genus, which include mucosal HPVs (Table 1) [2].

Classification of Human Papillomavirus by carcinogenic potential

Possibly high-oncogenic risk 26, 53, 66, 67, 68, 70, 73, 82,

**Table 2.** Classification of HPV genotypes based on carcinogenic potential

High-oncogenic risk 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59

**3.1. Primary route of transmission: Sexual contact with an infected partner**

Low-oncogenic risk 6, 11, 13, 30, 32, 34, 42, 44, 54, 61, 62, 69, 71, 72, 74, 81, 83, 84, 85, 86, 87, 89, 90

Epidemiology of Anogenital Human Papillomavirus Infections

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\*Adapted from Bouvard et al, on behalf of the WHO International Agency for Research on Cancer Monograph Working

Epidemiologic data supports that the primary route of HPVs transmission is via sexual contacts. The most important risk factors for prevalent infection as well as for acquisition or incidence in adults, are related to sexual behaviour variables: age at sexual debut and number of sexual partners, new, recent or lifetime for example [5-7]. Transmission may occur through peno-vaginal intercourse, but also via other sexual practices. Anal intercourse is also associated with HPV infection. History of receptive anal sex has been identified as an important risk factor for anal HPV infection among men [8-12]. Oral sex is also a possible route of HPV transmission as it has been associated with HPV oral infection [13-15]. Furthermore, digital-genital trans‐ mission is possible, as genital HPV genotypes have been found on fingers[16]. Insertive sex toys are also a possible of route of transmission[17]. Studies on genital HPV infection between women who have sex with women also suggest that HPV transmission is possible among

HPV genital infections can also origin from non-sexual route of transmission. For example, HPV DNA can be detected in genital or oral tract of newborns and children through perinatal/ vertical transmission [19-23]. Vertical transmission of HPV from mother to child (perinatal infection) was first reported in 1956 in a case of juvenile laryngeal papillomatosis[24]. Confir‐ mation of the perinatal transmission of HPV in different mucosa (genital, oral) was subse‐ quently supported by several studies although the route of transmission is not well understood[19-23, 25]. Direct maternal transmission during vaginal delivery or at caesarean section following early membrane rupture is possible as well as in utero through semen or ascending infection from mother's genital tract. Transplacental transmission seems possible since HPV DNA has been detected by PCR in amniotic fluid, placenta and cord blood [25, 26].

**Oncogenic potential Genotypes of HPV**

Group 2009 [3]

**3. Routes of transmission**

lesbian partners[18].

**3.2. Non-sexual routes of transmission**

Mucosal HPVs are also classified according to their oncogenic potential: low-oncogenic risk genotypes (LR-HPVs) and high-oncogenic risk genotypes (HR-HPVs). LR-HPVs may cause benign lesions of the anogenital mucosa such as *condylomata acuminata* (genital warts) while HR-HPVs are linked to the development of pre- and malignant lesions. The latest classification published by the World Health Organization's International Agency for Research on Cancer referred genotypes 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58 and 59 as HR-HPVs[3, 4]. This classification also included many other genotypes as possibly carcinogenic, such as genotypes 26, 53, 66, 67, 68 70, 73 and 82 (Table 2). These genotypes are referred as possibly carcinogenic because the evidence about their carcinogenicity are more limited. Oncogenic potential classification of HPVs is updated frequently with the occurrence of new epidemiologic evidence[5].


Classification of Human Alpha-Papillomavirus

\*Adapted from De Villiers et al., 2004 [1]

**Table 1.** Classification of species and genotypes of HPVs among the Alpha genus


Classification of Human Papillomavirus by carcinogenic potential

\*Adapted from Bouvard et al, on behalf of the WHO International Agency for Research on Cancer Monograph Working Group 2009 [3]

**Table 2.** Classification of HPV genotypes based on carcinogenic potential
