Papillomaviridae
Papillomaviridae is a family of viruses known as papillomaviruses, with several hundred types that can infect a wide range of hosts, including mammals, birds, amphibians, and reptiles. These viruses are non-enveloped and possess circular double-stranded DNA genomes. While many types are harmless and may not produce symptoms, certain strains can lead to the formation of tumors and papillomas (warts), and some are associated with various cancers. Human papillomavirus (HPV) is the most notable type affecting humans, with approximately two hundred strains, forty of which are known to be sexually transmitted.
HPV infection is common, affecting about half of sexually active individuals, often without obvious symptoms, making it easy for the virus to spread unknowingly. Different strains are responsible for different health outcomes; low-risk types typically lead to genital warts, while high-risk types can result in several cancers, including cervical and oropharyngeal cancer. Vaccines such as Gardasil and Cervarix have been approved to prevent HPV infections, particularly among adolescents, although they do not treat existing infections or prevent all types of HPV. Overall, Papillomaviridae represents a significant area of study in virology and public health due to its implications for human health and disease prevention.
Papillomaviridae
Papillomaviridae is a family of viruses known as papillomaviruses. Several hundred types of papillomaviruses exist. They can infect mammals, birds, amphibians, and reptiles. The infections cause tumors and papillomas (warts). Several types of papillomaviruses can cause cancer. Human papillomavirus (HPV) is the most common type that infects humans.
Origins
Papillomaviridae are non-enveloped, double-stranded deoxyribonucleic acid (DNA) viruses. They have circular genomes and are very small. Papillomaviridae used to be classified with the Polyomaviridae family of viruses in the Papovaviridae family. The two groups share similarities. They are both non-enveloped, double-stranded DNA viruses with circular genomes. They both cause similar viruses that produce tumors. However, the two groups were found to have distinct differences. They are not the same genome sizes and are organized differently. Eventually, they were split into their own respective families.
Papillomaviruses coevolved with their hosts. The viruses are host specific, meaning nearly all the viruses are specific to their natural host and typically do not infect other species—not even closely related species. However, multiple strains of papillomavirus can infect a particular species. An example is HPV, which has about two hundred different strains that affect humans.
Some types of papillomaviruses do not cause any symptoms. Some cause tumors, which can be cancerous. Others cause papillomas. The viruses go through active and latent (dormant) phases in the body, causing symptoms such as warts during active times and causing no symptoms during latent times.
Papillomaviruses can be transmitted by direct contact, sexual contact, and during birth. They infect the skin surfaces such as the hands and feet and mucosal cells of the genitals, anus, mouth, or airways. Different types of papillomas (such as flat or raised warts) are associated with different strains of papillomaviruses. The different strains also cause infection to particular parts of the body such as the genitals versus the feet.
Human Papillomavirus (HPV)
Human papillomavirus (HPV) is the most common type of papillomavirus that infects humans. It is different from the herpes simplex virus (HSV) that causes cold sores and genital sores and is from the family Herpesviridae. Nearly two hundred strains of HPV exist. Of these, about forty are sexually transmitted and cause warts on the mucous membranes such as the genital areas. HPV is found in the epithelial cells, which are the thin, flat cells on the surface of the skin as well as the surface of the anus, cervix, mouth, penis, throat, vagina, and vulva.
HPV is a sexually transmitted infection (STI) spread through sexual contact (anal or vaginal intercourse and oral sex) with infected persons. The virus infects the genital skin, mucous membranes, and bodily fluids. Condoms do not fully protect against the infection because the virus infects the skin surfaces not covered by the condom.
HPV affects about half of all sexually active people. Some types of HPV infections do not cause any symptoms and go away on their own; therefore, many people do not realize they are infected with HPV and unknowingly spread the virus to others. In addition, it can take years for symptoms to develop, making it difficult to know when or where a person contracted the infection.
Low-risk HPVs are the types that cause painful warts. These warts look like a cluster of small bumps usually in the genital area. The warts can be raised or flat or look like a head of cauliflower. Types 6 and 11 cause nearly 90 percent of all genital warts cases. These types also can cause respiratory papillomatosis, a condition in which tumors grow in the air passages from the nose and mouth into the lungs.
The types of HPV that cause cancer are not the same as the ones that cause warts. High-risk HPVs can cause cervical cancer; cancers of the anus, penis, vagina, or vulva; and oropharyngeal cancer (cancer of the back of the throat that also affects the base of the tongue and tonsils). Types 16 and 18 are responsible for causing many HPV-related cancers. High-risk HPV infections can be asymptomatic.
No test is available to detect HPV in men. Women can receive Pap tests, which screen for cervical cancer and HPV. HPV is diagnosed by the appearance of warts or by an abnormal Pap test result for women.
HPV Vaccines
The U.S. Food and Drug Administration (FDA) has approved three vaccines (Gardasil, Gardasil 9, and Cervarix) to protect against HPV. While these can prevent a person from acquiring most HPV infections, they cannot treat already existing cases. The vaccines do not protect against all types of HPV, meaning they cannot prevent all cases of warts or cancer. Women who receive the vaccines should still continue to be screened for cervical cancer. The vaccines also do not prevent STIs.
The vaccines can protect both males and females against HPV before they become sexually active and are potentially exposed to HPV infections. All adolescents aged eleven or twelve should receive the vaccines, which are given in three doses over six months. Males and females over this age and under age twenty-six can receive catch-up vaccines. Pregnant women should not receive the vaccines.
Bibliography
Chow, Louise T., Thomas R. Broker, and Bettie M. Steinberg. "The Natural History of Human Papillomavirus Infections of the Mucosal Epithelia." APMIS 118.6–7 (2010): 422–449. PDF. Web. 11 Mar. 2016. http://www.hu.ufsc.br/projeto‗hpv/The%20natural%20history%20of%20human%20papillomavirus%20infections%20of.pdf
De Villiers, Ethel-Michele, Claude Fauquet, Thomas R. Broker, and Hans-Ulrich Bernard. "Classification of Papillomaviruses." Virology 324.1 (June 2004): 17–27. ScienceDirect. Web. 11 Mar. 2016. http://www.sciencedirect.com/science/article/pii/S004268220400220X
"Human Papillomavirus (HPV)." Centers for Disease Control and Prevention. U.S. Department of Health and Human Services. Web. 11 Mar. 2016. http://www.cdc.gov/std/hpv/stdfact-hpv.htm
"Human Papillomavirus (HPV) Vaccines." National Cancer Institute. U.S. Department of Health and Human Services. Web. 11 Mar. 2016. http://www.cancer.gov/about-cancer/causes-prevention/risk/infectious-agents/hpv-vaccine-fact-sheet
Smith, Lauren. "Papillomaviridae." Stanford University. Stanford University. Web. 11 Mar. 2016. http://web.stanford.edu/~lsmith36/
Van Doorslaer, Koenraad. "Evolution of the Papillomaviridae." Virology 445.1–2 (Oct. 2013): 11–20. ScienceDirect. Web. 11 Mar. 2016. http://www.sciencedirect.com/science/article/pii/S0042682213002924