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The human papillomavirus (HPV) is the most common sexually transmitted infection amongst sexually active adults and adolescents in the world (Shors, 262). Not only the high prevalence of the virus makes it important, but also the wide range of infections that occur from it. As many as an100 HPVs have been completely described (Shors, 263). Many of the papillomaviruses cause benign papillomas or warts in the skin, such as on the hands, soles of the feet, and genitals or mucous membranes. HPV types 16 and 18 have been identified to be a cause of carcinomas of the cervix, vulva, vagina, anus, and penis (Shors, 263). Human papillomaviruses are non-enveloped, small double-stranded DNA viruses that are only epitheliotropic (Brown et al., 2008). The paper will describe in detail the structure, classification, the life cycle of the virus as well as the diseases it causes, the treatments of the diseases, and how the virus impacts public health.
Papillomaviruses are small, non-enveloped viruses with an icosahedral capsid with double-stranded, supercoiled, circular DNA as its genome (Willey, 938). Under Baltimore classification the papillomaviruses are classified as class I double-stranded DNA viruses (dsDNA). The papillomaviruses are placed in the family Papillomaviridae (Willey, 938). HPV is 8000 base pairs in length (Shors, 263). The HPV genome contains open reading frames (ORF) that encode for the non-structural proteins that are required for viral replication and the structural proteins that help form the viral coat (Brown et al., 2008). The ORFs are designated as early proteins E1-E7, and the late proteins L1 and L2 (Shors, 265). The non-coding long control region (LCR) controls the expression of the ORFs and contains a complex variety of transcription factor binding sites and is the viral origin of replication (Brown et al., 2008) The ORFs E6 and E7 encode oncoproteins that make contact with multiple regulatory pathways in the host cell to facilitate completion of the viral life cycle. The E6 and E7 ORFs interact with the tumor suppressor proteins p53 and pRb, as well as other cellular proteins in humans (Shors, 265). The L1 and L2 proteins encode the genes for the capsid or structural proteins of the virus (Shors, 265). The E2 protein in HPVs is in involved in virus replication and in the regulation of their gene expression (Brown et al., 2008).
HPVs only infect stratifying basal epithelial cells and this is where their life cycle occurs (Shors, 262). HPVs cannot infect the dermis of the skin because these cells are not metabolically active (Shores, 2009). A papillomavirus is able to infect the host by entering the basal epithelial cells through a break in the hostâ€™s skin (Shors, 2009). Once the virus has entered the cell, the virus uncoats and goes to the nucleus, where is releases its DNA (WHO, 2010). Once the virus is in the nucleus the activation of an upstream regulatory region that initiates expression of E1 and E2 occurs. These early proteins direct the host cell replication machinery to the viral origin of replication. This results in a quick rise of the viral genome. E1 acts as an ATP-dependent helicase that unwinds the double-stranded viral DNA and help recruit cellular factors to allow replication to proceed (Brown et al., 2008). E1 and E2 build mRNA molecules. The early genes, E4 and E5 assist in the virus genome production and control the epidermal growth factor. E2 helps control cell proliferation by regulating the expression of E6 and E7. E6 and E7 interfere with the host cells control of transcription and the cell cycle. E6 and E7 genes, respectively, interfere with the genes p53 and pRb. The late genes L1 and L2 encode for the viral capsid proteins for new viruses. The virion is assembled and matures to be shed by the sloughing of the stratum corneum (Shors, 266).
HPVs cause a wide range of infections from benign warts on the skin and in the throat to carcinomas of the cervix, vulva, vagina, anus, penis, as well as to the head and neck (Shors, 263). A person will develop genital warts after HPV has entered the body during vaginal and anal sex (CDC, 2009). HPV may also be passed on during oral sex (CDC, 2009). HPV can be passed between straight and same-partners, even when the infected partner has no signs or symptoms (CDC, 2009). An individual can be infected with HPV for years and not know that they are infected or that they are passing the virus on to their sexual partners (CDC, 2009). The symptoms of genital warts are the appearance of a small bump or group of bumps in the genital area. The bumps can be small or large, raised or flat, or shaped like a cauliflower (CDC, 2009). More than one type of HPV can infect a person at one time (CDC, 2009). Rarely does a pregnant woman pass on HPV to a baby during delivery (CDC, 2009). HPV is of such medical importance since it causes carcinomas. Products of the immune system such as interferons, apoptosis, and phagocytosis clear most HPV infections within two years (CDC, 2009). A personâ€™s immune system that is not able to fight off HPV will likely lead to cancer. The high-risk cancer causing HPV types are 16, 18, 45 and 31 (Shors, 265). These HPVs cause cancer by having their proteins E6 and E7 bind and inactivate the tumor suppressing genes p53 and pRb (Meelis et al., 2009). The inactivation of these suppressor genes leads to the disruption of the normal cell cycle and chromosomal abnormalities (Shors, 265). It often takes years for an HPV infection to cause cancer and there are no obvious symptoms that can be used for diagnosis. In contrast warts can develop within a few weeks or months (CDC, 2009).
Treatment for warts includes the following: waiting to see if the wart goes away on its own, freezing the abnormal cells with liquid nitrogen, conization, and loop electrosurgical excision procedure are used to remove the abnormal cells (CDC, 2009). Also, people who suffer from genital warts may use medications prescribed from doctors (CDC, 2009). Women that are diagnosed with cervical cancer by use of a Pap test can be treated with removal of the abnormal cells. When the cancer is in a progressed stage more intense treatments such a chemotherapy, radiation, and radical hysterectomy may have to be used (CDC, 2009). Genital warts and cervical can be prevented by the use of the vaccines Gardasil and Cervarix (CDC, 2009). Females ages 26 years old and under should receive the 3 doses of the HPV vaccines. Men and young boys are also eligible to receive the vaccine. The vaccines do not cure HPV, but are preventative measures.
Human papillomaviruses infects both heterosexual and homosexual men and women from all ethnic and racial groups, as well as social economic groups (CDC, 2009). HPV is not a discriminatory virus. HPV can infect every single person on earth hence, to why it is the most common sexually transmitted infection in world. HPV currently infects approximately 20 million Americans (CDC, 2009). An estimated 6 million people become infected each year (CDC, 2009). The commonality of HPV makes it so that at least 50% of sexually active men and women will acquire it at some point in their lives (CDC, 2009). Only about 1% of sexually active adults in the U.S. will develop genital warts (CDC, 2009). About 12,000 women will be diagnosed in the U.S. with cervical cancer each year (CDC, 2009). A disease termed recurrent respiratory papillomatosis infects less than 2,000 children in the U.S. Most men that become infected with HPV do not develop any severe health issues. The main health problem that develops in men is genital warts. Gay and bisexual men are more likely to develop anal cancer than heterosexual men (CDC, 2009). Also, men with weak immune systems, including those that immunocompromised from HIV or other autoimmune diseases have a higher chance to develop anal cancer. Men and women that engage in sexual activity at an early age, have multiple sex partners, or have a sex partner who has had multiple sexual partners are at higher risk of getting genital HPV (CDC, 2009).
Overall, HPV is a virus that has a huge impact medically for people all over the world. HPV is such a common infection that we ourselves may be infected or know someone that is infected. The cause for HPV infecting so many men and women are the unsafe sexual practices, and lack of knowledge of the virus. This lack of safe practices and knowledge leads to HPV infections that can cause warts on the skin and a variety of carcinomas. As the years pass by hopefully more people become educated in the infections that HPVs cause and how to protect themselves and get the vaccines to ensure their health. These vaccines will protect individuals from genital warts and females from cervical cancer. More education about HPV and how it is the cause of cervical cancer should be more prevalent in developing countries, because it is one of the leading killing cancers of these women.