Human papillomavirus (HPV) is a large group of closely related viruses, some of which cause warts--including sexually transmitted genital warts--and some of which can cause cervical cancer. The types of HPV with the greatest likelihood of causing cancer are classified as "high-risk." There are 15 types of "high-risk" HPVs that are sexually transmitted. According to the National Cancer Institute, HPV types 16 and 18 cause about 70 percent of all cases of cervical cancer.
HPV-16
All papillomaviruses cause warts, which are a kind of benign tumor. "High risk" HPVs are more likely than "low-risk" types to cause cancer. That does not mean that infection with them puts you at high risk for developing cervical cancer: The great majority of high-risk HPV infections go away on their own.
Persistent infection with a high-risk type of HPV increases your risk for cervical cancer. In a study published in the February 2010 issue of "Journal of Medical Virology", Dr. Nielsen Kjaer found that HPV-16 is among the most persistent types of HPV. Two years after the initial infection, about 4 percent of women are still infected with HPV-16.
Dr. Paola Menegazzi reports in "Infectious Diseases in Obstetrics and Gynecology" that HPV-16 also is among the most common types of HPV in infected women, and that pre-cancerous cervical lesions of moderate risk for developing into cancer (called cervical intraepithelial neoplasia grades 2 and 3) are associated with HPV-16 infection.
HPV-18
Dr. Menegazzi's study found that like HPV-16 infection, HPV-18 infection is associated with the presence of grade 2 and 3 cervical intraepithelial neoplasia. She also reports that while HPV-18 is the second-most common type of HPV in Europe, it is not among the most common types of HPV infection in the United States.
Other High Risk Types
There are 15 known sexually transmitted "high-risk" types of HPV: -16, -18, -31, -33, -35, -39, -45, -51, -52, -56, -58, -59, -66, -68, and -73. Dr. Kjaer's article states that HPV types -31 and -58, along with HPV-16, are the most persistent types. These three types are closely related species, classified as group alpha 9. Dr. Menegazzi finds that following HPV-16, HPV-52 is the most common in Asia and North America. She also reports that infection with high-risk types -31 and -51 are associated with grade 2 and 3 cervical intraepithelial lesions.
References
- National Cancer Institute: Human Papillomaviruses and Cancer
- "Journal of Medical Virology;" Persistence of High-Risk Human Papillomavirus Infection in a Population-Based Cohort of Danish Women; Ann Nielsen; April 2010
- "Infectious Diseases in Obstetrics and Gynecology;" Human Papillomavirus Type Distribution and Correlation with Cyto-Histological Patterns in Women from the South of Italy;" Paola Menegazzi et al.; December 2009
