Human papillomavirus

Human papillomavirus
Name	Human papillomavirus
Synonyms	HPV
Caption	Transmission electron micrograph of HPV virions
Field	Infectious disease, Gynecology, Dermatology
Symptoms	None, warts, precancerous lesions
Complications	Cervical cancer, Oropharyngeal cancer, Anal cancer
Causes	Infection with human papillomavirus
Risks	Sexual activity, weakened immune system
Diagnosis	Pap test, HPV test, Biopsy
Prevention	HPV vaccines, Condoms
Treatment	Cryotherapy, Surgical excision, Laser surgery
Frequency	Very common

Human papillomavirus. It is one of the most common sexually transmitted infections globally, with a vast majority of sexually active individuals encountering it at some point. The virus comprises a large family of over 200 related types, which are classified by their associated disease risk, ranging from harmless to cancer-causing. While most infections are transient and asymptomatic, persistent infection with certain high-risk types is a necessary cause of several major cancers.

Types and classification

The numerous types are classified numerically based on genetic sequence differences identified through techniques like PCR. Clinically, they are categorized as either low-risk or high-risk based on their oncogenic potential. Low-risk types, such as HPV6 and HPV11, are primarily associated with benign anogenital warts and recurrent respiratory papillomatosis. High-risk, or oncogenic, types, including HPV16, HPV18, HPV31, and HPV45, are definitively linked to the development of malignancies. The International Agency for Research on Cancer, a branch of the World Health Organization, has classified several types as carcinogenic to humans. The E6 and E7 oncoproteins produced by high-risk types are key drivers of cellular transformation by inactivating host tumor suppressor proteins like P53 and pRb.

Transmission and risk factors

Primary transmission occurs through direct skin-to-skin or mucosal contact, most commonly via vaginal, anal, or oral sexual activity. The Centers for Disease Control and Prevention notes it is so common that nearly all sexually active people get it without vaccination. Non-sexual transmission routes, such as perinatal transmission from mother to infant during delivery, can lead to Juvenile-onset recurrent respiratory papillomatosis. Key risk factors include a high number of sexual partners, early age of first sexual intercourse, co-infection with other agents like HIV or Chlamydia trachomatis, and immunosuppressive conditions or medications. The use of Condoms reduces but does not eliminate transmission risk.

Diseases and symptoms

Most infections are subclinical and resolve spontaneously within two years. When disease occurs, manifestations depend on the viral type and infection site. Low-risk types cause genital warts and warts on other skin surfaces. High-risk types cause precancerous lesions, which can progress to invasive cancers if untreated. In women, persistent infection is the principal cause of Cervical cancer, as well as cancers of the vulva, vagina, and anus. In both men and women, it is increasingly implicated in Oropharyngeal cancer, particularly of the tonsils and base of the tongue, and Penile cancer. The Bethesda system is used to classify cervical cytology results from tests like the Pap smear.

Prevention and screening

Primary prevention is achieved through vaccination. Major prophylactic vaccines, such as Gardasil and Cervarix, target the most common high-risk and low-risk types. The Advisory Committee on Immunization Practices recommends routine vaccination for adolescents. Secondary prevention relies on organized screening programs. For cervical cancer, this involves regular Pap tests, which can detect abnormal cells, and standalone HPV DNA testing to identify high-risk infections. The introduction of the ThinPrep method improved cytology sample quality. Screening guidelines are established by bodies like the American Cancer Society and the U.S. Preventive Services Task Force.

Treatment and management

There is no antiviral treatment to eliminate the infection itself; therapy is directed at the diseases it causes. For visible warts, options include patient-applied therapies like Imiquimod or provider-administered Cryotherapy, chemical ablation, or laser ablation. Precancerous cervical lesions, known as Cervical intraepithelial neoplasia, are often treated with LEEP or Cold knife conization. Management of oropharyngeal cancers typically involves a combination of Radiation therapy, Chemotherapy, and surgery, with protocols guided by organizations like the National Comprehensive Cancer Network. The Prognosis for HPV-associated cancers is often better than for similar cancers not linked to the virus.

Epidemiology

It is considered the most prevalent sexually transmitted infection worldwide. The World Health Organization estimates that cervical cancer, caused by persistent infection, is the fourth most common cancer among women globally, with a disproportionate burden in lower-resource regions like Sub-Saharan Africa and Latin America. The prevalence of high-risk types varies geographically and demographically. Since the introduction of vaccination programs in countries like Australia, United Kingdom, and the United States, there has been a marked decrease in the prevalence of targeted types and associated precancerous lesions in vaccinated cohorts, as documented by surveillance systems like NHANES.

Category:Sexually transmitted diseases and infections Category:Infectious causes of cancer Category:Papillomaviruses