Friday, November 3, 2006

What are human papillomaviruses (HPVs)?

There are over 100 types of papillomaviruses (HPVs) that infect humans. Of these, more than 40 types can infect the anogenital tract (genital tract and anus) of men and women and cause genital warts (known as condylomata acuminata or venereal warts). A subgroup of the HPVs that infect the anogenital tract (genital tract and anus) can lead to precancerous changes in the uterine cervix and cause uterine, cervical cancer. HPV infection also is associated with the development of other anogenital cancers in women. The HPV types that cause cevical cancer also have been linked with both anal and penile cancer in men as well as a subgroup of head and neck cancers in both women and men. Genital warts and HPV infection are transmitted primarily by sexual intimacy, and the risk of infection increases as the number of sexual partners increase.

The most common HPV types that infect the anogenital tract are HPV types 6, 11, 16, and 18 (HPV-6, HPV-11, HPV-16, and HPV-18), although other HPV types can also infect the anogenital tract. Among these, HPV-6 and HPV-11 are most commonly associated with benign lesions such as genital warts and mild dysplasia of the cervix (potentially precancerous changes in the appearance of cervical cells under a microscope) and are termed "low-risk" HPV types. In contrast, HPV-16 and HPV-18 are the types found in the majority of cervical and anogenital cancers as well as severe dysplasia of the cervix. These belong to the so-called "high-risk" group of HPVs.
Other, different HPV types infect the skin and cause common warts elsewhere on the body. Some types of HPVs (e.g., HPV 5 and 8) frequently cause skin cancers in people who have a condition known as epidermodysplasia verruciformis.