Human papillomavirus infection

Human papillomaviruses (HPV) are a group of DNA viruses that are now classified into more than 100 different types. HPV are non-enveloped, double-stranded DNA viruses (dsDNA) and belong to the Papillomaviridae family and the genera Alphapapillomavirus, Betapapillomavirus and Gammapapillomavirus. They infect epithelial cells of the skin and various mucous membranes and can cause uncontrolled tumor-like growth in the infected cells. These tumors are usually benign and lead to the formation of warts on the affected area of skin or mucous membranes (the site of infection). If the infection occurs in the genital or anal area (usually through sexual intercourse), genital warts (e.g. genital warts) form.

However, some HPV types can also cause malignant changes, especially cervical cancer in women. A considerable proportion of vaginal, penile and anal carcinomas are probably also the result of such HPV infections. HPV infection also seems to be involved in the development of basal cell carcinoma ("white skin cancer"). HPV can also be transmitted to the oral mucosa through oral sex and trigger oral tumours there.

The gene products of these viruses, especially those of the E6 and E7 genes, prevent programmed cell death (apoptosis) and make repair of the DNA double strand impossible. The skin lesions caused by papillomaviruses are often not visible to the naked eye. The degenerations caused by the viruses pose particular problems in the case of uncontrolled growth, for example if the body's defences are weakened by another disease.

Human papillomaviruses were studied in particular in the laboratories of Harald zur Hausen (who was awarded the Nobel Prize for discovering the link with cervical cancer, among other things) and Gérard Orth of the Institut Pasteur.

Virus Groups

A distinction must be made between classification (based on the clinical picture and course of the disease) and taxonomy (based on genetic relationship).

Classification

To date, 124 HPV types have been fully described. About 30 of them almost exclusively infect the skin and mucosa in the anogenital region (anus and genitals). The genital HPV types can generally be divided into two groups, the low-risk and the high-risk types. The classification is based on the risk type: a few pathogens occur extremely frequently in connection with carcinomas.

• The high-risk types have been identified in 99.7 % of all cases of cervical carcinoma (cancerous tumours of the cervix). In turn, the majority of cervical carcinomas (about 70%) are caused by high-risk types 16 and 18, followed by genotypes 31 and 33.
• The low-risk types are almost never directly involved in the development of cervical carcinoma. In the case of multiple infections (infections with more than one HPV genotype), however, they can also be detected in cervical carcinomas, but then together with a clinically relevant high-risk type.

The guys are:

1. "low-risk viruses

HPV 6 and 11 are included in this group because, as the main causes of warts in the genital area (condylomata acuminata, also known as "genital warts"), they are not potentially life-threatening pathogens. Other low-risk types are 40, 42, 43, 44, 54, 61, 70, 72, 81 and CP6108.

2. "high-risk viruses

The second group mainly includes HPV 16, 18, 31 and 33, but also 35, 39, 45, 51, 52, 56, 58, 59, 68, 73 and 82. In almost every case of cervical carcinoma (cancer of the epithelial tissue of the cervix), at least one of the high-risk HPV groups is detectable in HPV screening. Some cancers of the anus and mouth are also considered HPV-associated.

3. possibly "high-risk" viruses

These include HPV 26, 53 and 66.

4. Viruses without clear risk assignment (HPV genotypes of undetermined risk)

In 2005, the IARC officially classified genotypes 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and 66 as carcinogenic. The dangerous virus subgroups have been shown to be involved not only in the development of cervical cancer, but are also found in cancers of the penis, vulva (external female genitalia), anus and throat.

System

The decision on different taxa (taxonomic, i.e. relationship groups) is deliberated and made by an international body, the International Committee on Taxonomy of Viruses (ICTV). As of November 2018, the taxonomy of the Papillomaviridae is as follows (for genera with only a single species, the species is numbered 1 and is not specifically listed):

·         Family Papillomaviridae

·         Subfamily Firstpapillomavirinae

·         Genus Alphapapillomavirus (with species Alphapapillomavirus 1 to 14)

·         Genus Betapapillomavirus (with species Betapapillomavirus 1 to 6)

·         Genus Gammapapillomavirus (with species Gammapapillomavirus 1 to 27)

·         Genus Deltapapillomavirus (with species Deltapapillomavirus 1 to 7)

·         Genus Epsilon papillomavirus (with species Epsilon papillomavirus 1 and 2)

·         Genus Zetapapillomavirus

·         Genus Etapapillomavirus

·         Genus Thetapapillomavirus

·         Genus Iotapapillomavirus (including species Iotapapillomavirus 1 and 2)

·         Genus Kappapapillomavirus (with species Kappapapillomavirus 1 and 2)

·         Genus Lambdapapillomavirus (with species Lambdapapillomavirus 1 to 5)

·         Genus Mupapillomavirus (with species Mupapillomavirus 1 to 3)

·         Genus Nupapillomavirus

·         Genus Xipapillomavirus (with species Xipapillomavirus 1 to 5)

·         Genus Omicron papillomavirus

·         Genus Chipapillomavirus (with species Chipapillomavirus 1 to 3)

·         Genus Pipapillomavirus (with species Pipapillomavirus 1 and 2)

·         Genus Rhopapillomavirus (with species Rhopapillomavirus 1 and 2)

·         Genus Sigmapapillomavirus

·         Genus Taupapillomavirus (with species Taupapillomavirus 1 to 3)

·         Genus Upsilon papillomavirus (with species Upsilon papillomavirus 1 to 3)

·         Genus Phipapillomavirus

·         Genus Psipapillomavirus (with species Psipapillomavirus 1 to 3)

·         Genus Omegapapillomavirus

·         Genus Dyodeltapapillomavirus

·         Genus Dyoepsilon papillomavirus

·         Genus Dyozetapapillomavirus

·         Genus Dyoetapapillomavirus

·         Genus Dyothetapapillomavirus

·         Genus Dyoiotapapillomavirus (including species Dyoiotapapillomavirus 1 and 2)

·         Genus Dyocappapillomavirus (with species Dyocappapillomavirus 1 to 5)

·         Genus Dyolambdapapillomavirus

·         Genus Dyomupapillomavirus

·         Genus Dyonupapillomavirus

·         Genus Dyoxipapillomavirus (with species Dyoxipapillomavirus 1 and 2)

·         Genus Dyoomicron papillomavirus

·         Genus Dyopipapillomavirus

·         Genus Dyorhopapillomavirus

·         Genus Dyosigmapapillomavirus

·         Genus Dyotaupapillomavirus

·         Genus Dyophipapillomavirus

·         Genus Dyoupsilon papillomavirus

·         Genus Dyopsipapillomavirus

·         Genus Dyoomegapillomavirus

·         Genus Treisdeltapapillomavirus

·         Genus Treisepsilon papillomavirus

·         Genus Treiszetapillomavirus

·         Genus Treisetapapillomavirus

·         Genus Treisthetapapillomavirus

·         Genus Treisiotapapillomavirus

·         Genus Treiskappapillomavirus

·         Subfamily Secondpapillomavirinae

·         Genus Alefpapillomavirus

Transmission

The infection occurs mainly through skin contact, and for certain virus types primarily through unprotected sexual intercourse (genital, anal or oral sex). The HPV infection is therefore one of the most common infections transmitted through sexual intercourse, but often the infection goes unnoticed. Condoms can halve the risk of infection. More rarely, the viruses are also transmitted through shared towels, drinking glasses or toothbrushes. In the context of an already existing infection, pubic hair removal by shaving can lead to infection of previously unaffected areas of the body.