Human papillomavirus: what is it?

Human Papillomavirus or HPV (HPV for Human papillomavirus in English) is a virus DNA double-strandedcircular of the family of Papillomaviridae. Very resistant in the environment, it is transmitted through the skin and is responsible forsexually transmitted infections.

The different types of human papillomavirus infection

There are 200 genotypes known. Most often the infection is asymptomatic and resolves spontaneously. “Low risk” HPV types (HPV6 and HPV11) cause mild illnesses such as condylomasmall warts very contagious and recurrent. In the form of growths, isolated or in clusters, these lesions are located on the anal margins and the genitals (foreskin and glans in men, vulva and neck of theuterus in women). No oral treatment currently exists but some techniques application local (chemical, laser) allow their destruction.

The “high risk” HPV types (HPV16 and HPV18) are viruses oncogenes and represent 70% of cancer of the cervix. In this case, the persistent presence of the virus modifies the cells of the cervix causing anomalies which can evolve into precancerous lesions or even cancer in the absence of treatment.

Characteristics of Human Papillomavirus

Structurally, they are small virus (52 to 55 nm in diameter) with a capsid icosahedral (geometric shape consisting of 20 sides, each consisting of an equilateral triangle). They are non-enveloped viruses that are very resistant to the environment. All Papillomaviruses contain a genome at DNA double-stranded (8,000 bases) coding for proteins early proteins with a regulatory (E1 and E2) and transforming (E6 and E7) function and for late proteins (L1 and L2) involved in the formation of the capsid.

The target cells of HPV are the stem cells of squamous epithelial tissues (skin, mucosa). The stages of the viral multiplication cycle are closely linked to the differentiation of epithelial cells. Cell entry is through endocytosis. The maintenance and replication of the’DNA viral take place in the nucleus of basal cells of the’epithelium. Then the production of new viral DNA and the synthesis of capsid proteins take place in the upper layers of the infected epithelium. The assembly as the liberation of the virus mature is done in the squamous cells of keratin.

Mechanism of carcinogenesis

The production of HPV is linked to the program of differentiation of keratinocytes. In condyloma, papilloma and dysplasias mild to moderate, viral DNA remains as an episome (molecule of DNA that can replicate autonomously) and the production of virions is observed in the upper layers of the infected epithelium.

In cases of high-grade cancers and dysplasia, E6 and E7 are expressed throughout the infected epithelium and no virions are produced. The viral DNA is then randomly integrated into the chromosomes of the host cell. The E6 protein blocks theapoptosis cell and the E7 protein induces cell proliferation.

The development of a Cancer is a rare and slow process associated with “high risk” HPV infection involving multiple steps over a duration 15 years and over. Only the vaccination practiced before the start of the sex life provides protection. It has been recommended since January 2021 for all girls and boys aged 11 to 14.