Human Papillomavirus (HPV)

 

by Jennifer Ayars

Overview

Over 100 different types of HPV, or human papillomavirus, have been identified.  This group of DNA-based viruses is named papillomaviruses because certain types may cause papillomas, or benign epidermal tumors (warts).  HPVs may cause common warts on hands and feet or warts in the throat or genitals (9). 

 

HPV may cause genital warts, or condylomata acuminatum or venereal warts, around the genitals or anus.  Appearance of genital warts may occur within weeks, months or years following sexual contact with an infected HPV individual.  Genital HPV types are categorized into “low-risk” and “high-risk” viruses (15).  HPV-6 and HPV-11 cause approximately 90% of genital warts (13).  HPV types causing genital warts are considered “low-risk” viruses because cancer rarely develops (8).

 

“High-risk” oncogenic HPVs are associated with various forms of cancer.  Sexually transmitted, high-risk HPV strains include the following: 16, 18, 31, 35, 39, 45, 51, 52, 56, 58, 59, 68 and 69.  Such strains typically cause flat, abnormal growths.  Most high-risk HPV infections, however, go away without any treatment and therefore do not result in cancer (9).  HPV-16 and HPV-18 cause approximately 70% of cervical cancers (13).  High-risk types can lead to cancers of the “cervix, vulva, anus, or penis” (10).       

 

Discovery

In the early 1900s, epidemiologists noted that prostitutes commonly suffered from cervical cancer, but nuns (who were not sexually active prior to entry into the convent) were rarely afflicted.  In addition, scientists observed a high rate of cervical cancer among women who were married to men whose former spouses died from the disease.  Such population-based studies led scientists to conclude that a sexually transmitted agent caused cervical cancer.  In the late 1970s, German researchers discovered the agent to be HPV.  Global epidemiologic studies confirmed the causal relationship between cervical cancer and HPV infection (4).

 

Transmission

HPV is highly contagious.  Both men and women may acquire HPV.  Some types of HPV may be transmitted via skin-to-skin personal contact, while other types are sexually transmitted through genital contact (vaginal, oral and anal sex) with an infected partner (10).  Over 30 types of HPV are sexually transmitted (3).  In rare cases, a mother can pass HPV to her baby during vaginal delivery (7).   

 

Reservoir

Humans are the reservoir for HPV.  The virus lives in skin or mucous membranes (7).

 

Etiology

HPV is a small, non-enveloped DNA virus belonging to the Papovaviridae family.  The circular, double-stranded genome (approximately 8-kb long) contains an icosahedral protein capsid (15).  The HPV genome “encodes for 6 early proteins (E1-E7) responsible for virus replication and 2 late proteins, LI and L2, which are the viral structural proteins” (14). 

The course of HPV infection may be modified by the strain of virus; different physical, chemical and biological agents; and host genetic make-up and defense mechanisms.  The mechanism of the transforming proteins is highly complex and not fully understood (5). 

 

Signs and Symptoms

Like many sexually transmitted infections, HPV infections usually cause no symptoms.  Despite exhibiting no symptoms, if infected with the virus, one can still spread HPV and develop complications.  Genital warts and cervical cancer are two of the most common problems identified with HPV.  Genital warts may appear in “cauliflower-like” clusters and can be raised or flat, and small or large.  In women, genital warts may grow on the vulva and cervix, and inside and around the vagina and anus; in men, genital warts may grow on the scrotum, penis or around the anus.  Genital warts may also appear in the mouth or throat as a result of oral sex with an infected partner (10). 

 

Diagnosis

Medical personnel typically diagnose genital warts simply by viewing them with the naked eye.  Additional diagnostic tools include Pap smears, colposcopies, biopsies and HPV testing (to find HPV on the cervix – test looks for viral DNA) (9).

 

Treatment

There is no cure for the human papillomavirus, but most HPV infections are harmless and resolve without treatment.  However, options are available to treat resultant health problems such as genital warts, cervical cell changes and cervical cancer.  Although genital warts may disappear with or without treatment, the virus may still linger and be transmitted to partners.  Warts may be treated with different creams, solutions, medications, freezing, burning, laser treatment or surgery; yet, they often return because the virus is still in the body (10).  If precancerous cell changes are detected in women, treatment options may include cryotherapy, laser surgery or LEEP (loop carries electrical current) to remove cell abnormalities (11).

 

Control and Prevention

To detect cell changes caused by HPV, regular Pap smear tests for all women are advisable.  If HPV is detected early by Pap tests, cervical cancer may be preventable or treatable.  Only very few cases of HPV infection actually lead to cervix cancer (1).

 

Gardasil is a HPV vaccine that may prevent infection in females.  Gardasil has proven 95-100% effective against HPV types 6, 11, 16, and 18 (13).  Together, these four HPV types are responsible for 70% of cervical cancers and 90% of genital warts (8).  In June 2006, the Food and Drug Administration (FDA) approved the vaccine for girls and women 9-26 years old and recommends administration before the females become sexually active (13).  Currently, there is no approved HPV test or HPV vaccine for men (6).

 

Lowering chances of obtaining HPV may be accomplished through abstinence, limiting one’s number of sex partners and choosing a sex partner who has had few partners (11).  Some studies suggest that condom use by males may protect women against some types of HPV infection (7).

 

Incidence

At least 50% of individuals who have had sexual intercourse will contract HPV at some point in their lives.  Individuals are more likely to have HPV if they had sex at a young age or have multiple sex partners (who have had multiple partners) (13).

 

The Centers for Disease Control and Prevention (CDC) cites approximately 6.2 million reported new cases of sexually transmitted HPV infections annually (10).  At least 20 million Americans are currently infected (2).  Genital HPV is the top sexually transmitted virus in the United States (8).  Between 10-15 million Americans are infected with high-risk HPV types linked with cervical cancer.  Risk of cervical cancer is increased in women with suppressed immune systems (ex. HIV or AIDS) or women who smoke cigarettes (11).

 

World Health Organization research suggests that HPV caused approximately 500,000 cases and 250,000 deaths from cervical cancer in 2002, with about 80% of those deaths taking place in developing countries (14).  Cervical cancer is the second leading cause of death among females worldwide (15).  Over 440 million cases of genital HPV infection are estimated worldwide (12).   

 

Internet References

 

1.  American Cancer Society. “What Every Woman Should Know About Cervical Cancer and the Human Papilloma Virus.”  Written 07/10/2006. URL: http://www.cancer.org/docroot/CRI/content/CRI_2_6x_What_Every_Woman_Should_Know_About_Cervical_Cancer_and_the_Human_Papilloma_Virus.asp accessed 12/05/07.

 

2.  American Social Health Association. “HPV (Human Papillomavirus) > Background   Information.”  Written 2007.  URL: http://www.ashastd.org/learn/learn_hpv_bkgd.cfm accessed 12/05/07.

 

3.  American Social Health Association. “HPV (Human Papillomavirus) > Fast Facts.”  Written 2007.  URL: http://www.ashastd.org/learn/learn_hpv_facts.cfm accessed 12/05/07.

 

4.  ANON.  “Story of Discovery…Preventing Cervical Cancer.” Date unavailable. URL: http://plan2000.cancer.gov/resrch_prog/chap6/cervical.htm accessed 12/05/07.

 

5.  Cann, Dr. Alan. “Papovaviruses.”  Updated 02/16/1999. URL: http://www.tulane.edu/~dmsander/WWW/335/Papovaviruses.html accessed 12/05/07.

 

6.  Centers for Disease Control and Prevention.  “Common Questions about HPV and Cervical Cancer.”  Reviewed 08/28/07.  URL: http://www.cdc.gov/std/hpv/common-questions.htm accessed 12/05/07.

 

7.  Centers for Disease Control and Prevention.  “Genital HPV Infection – CDC Fact Sheet.” Reviewed 05/2004.  URL: http://www.cdc.gov/std/HPV/STDFact-HPV.htm accessed 12/05/07.

 

8.  Centers for Disease Control and Prevention.  “HPV – Common Infection. Common Reality.” Reviewed 07/11/07.  URL: http://www.cdc.gov/std/hpv/common-downloads.htm accessed 12/05/07.

 

9.  National Cancer Institute. “Human Papillomaviruses and Cancer: Questions and Answers.” Reviewed 06/08/2006.  URL: http://www.cancer.gov/cancertopics/factsheet/Risk/HPV accessed 12/05/07.

 

10. National Institute of Allergy and Infectious Diseases.  “Human Papillomavirus and Genital Warts.”  Updated 11/23/07. URL:

http://www3.niaid.nih.gov/healthscience/healthtopics/human_papillomavirus/overview.htm accessed 12/05/07.

 

11. Planned Parenthood.  “HPV.”  Updated 06/28/07.  URL: http://www.plannedparenthood.org/sexual-health/std/hpv.htm accessed 12/05/07.

 

12. The Journal of the American Medical Association.  “Human Papillomavirus Infection.”  Vol. 297 (8), 02/28/07.  URL: http://jama.ama-assn.org/cgi/content/full/297/8/912 accessed 12/05/07.

 

13. U.S. Food and Drug Administration.  “HPV (human papillomavirus).”  Written 06/2006.  URL: http://www.fda.gov/womens/getthefacts/hpv.html accessed 12/05/07.

 

14. World Health Organization. “Biologicals - Human Papillomavirus.” Written 2007.  URL: http://www.who.int/biologicals/areas/human_papillomavirus/en/ accessed 12/05/07.

 

15. World Health Organization.  “Initiative for Vaccine Research (IVR) – Human papillomavirus.”  Written 2007.  URL: http://www.who.int/vaccine_research/diseases/viral_cancers/en/index3.html accessed 12/05/07.