HPVs

Human papillomaviruses (HPVs) are a diverse group of nonenveloped, double-stranded DNA viruses in the Papillomaviridae family that infect keratinocytes of the skin and mucous membranes. There are more than 200 HPV types, broadly categorized as low-risk and high-risk based on disease association. The viral genome is about 8 kilobases in length and encodes early (E) and late (L) proteins; high-risk types produce E6 and E7 oncoproteins that can disrupt p53 and RB pathways, contributing to malignant transformation in persistent infections.

HPV infection typically occurs in basal epithelial cells through microabrasions. Most infections are asymptomatic and cleared by the immune system within months to a couple of years. However, persistent infection with certain high-risk types, especially HPV16 and HPV18, is associated with cancers of the cervix, anus, oropharynx, vulva, vagina, and penis. Low-risk types, such as HPV6 and HPV11, commonly cause benign warts on the genitals or hands and feet and may cause respiratory papillomatosis in the larynx.

Transmission is mainly via sexual contact but nonsexual routes can occur for skin warts. Condoms reduce risk but do not fully prevent HPV transmission. Prevention relies on vaccination and screening. Prophylactic vaccines (for example, Gardasil 9 and Cervarix) protect against the most common high-risk types and, in the case of Gardasil 9, additional low- and high-risk types. Vaccination is recommended for preteens and is often extended to older ages by public health guidelines. Screening programs include cervical cytology (Pap tests) and HPV DNA testing to detect precancerous lesions.

There is no licensed antiviral therapy to clear an established HPV infection; treatment focuses on managing warts or precancerous lesions. Ongoing surveillance and treatment of precancerous changes reduce cancer risk. HPV-related cancers remain a significant public health concern worldwide, though vaccination and screening have reduced incidence in many populations.