Human papillomavirus

Human papillomavirus: HPV. A family of over 100 viruses including those which cause warts and are transmitted by contact. Some types of HPV are associated with tumors of the genital tract including, notably, cancer of the cervix.

Of the more than 100 types of HPVs, over 30 types can be passed from one person to another through sexual contact. Most genital HPV infections come and go over the course of a few years. However, sometimes HPV infection may persist for many years, with or without causing cellular abnormalities.

The majority of HPVs produce warts on the hands, fingers, and even the face. Most of these viruses are thus innocuous, causing nothing more than cosmetic concerns. HPVs also can cause painful plantar warts (on the sole of the foot).

Several types of HPV, however, are confined primarily to the moist skin of the genitals, producing genital warts and markedly elevating the risk for cancer of the cervix.

Genital warts (technically known as condylomata acuminatum) are most commonly associated with two HPV types, HPV-6 and HPV-11. The warts may appear within several weeks after sexual contact with a person who is infected with HPV, or they may take months or years to appear, or they may never appear. HPVs may also cause flat, abnormal growths in the genital area and on the cervix (the lower part of the uterus that extends into the vagina). However, HPV genital infections usually cause no symptoms.

HPVs are now recognized as the major cause of cervical cancer. HPVs may play a role in cancers of the anus, vulva, vagina, and some cancers of the oropharynx (the middle part of the throat that includes the soft palate, the base of the tongue, and the tonsils). Infection with HPV is also a risk factor for penile cancer (cancer of the penis).

Some types of HPVs are referred to as "low-risk" viruses because they rarely cause cancer. HPVs that are more likely to lead to the development of cancer are referred to as "high-risk." Both low- and high-risk types of HPVs can cause the growth of abnormal cells, but generally only the high-risk types of HPVs may lead to cancer.

Sexually transmitted, high-risk HPVs include types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 69, and possibly a few others. These high-risk types of HPVs cause growths that are usually flat and nearly invisible, as compared with the warts caused by types HPV-6 and HPV-11.

A risk factor for HPV infection is a history of many sexual partners. Although HPV infections may go away on their own without causing any type of abnormality, infection with high-risk HPV types increases the chance that mild cellular abnormalities will progress to more severe ones and to cervical cancer. Still, of the women who do develop abnormal cell changes with high-risk types of HPVs, only a small percentage would develop cervical cancer if the abnormal cells were not removed.

Studies suggest that whether a woman develops cervical cancer depends on a variety of factors acting together with high-risk HPVs. The factors that may increase the risk of cervical cancer in women with HPV infection include smoking and having many children.

HPVs produce proteins known as E5, E6, and E7. These proteins interfere with the cell functions that normally prevent excessive growth. For example, HPV E6 interferes with the human protein p53. This protein is present in all people and acts to keep tumors from growing.

Vaccines for certain papillomaviruses, such as HPV-16 and HPV-18, are being studied in clinical trials for the prevention of cervical cancer and similar trials for other types of cancer are planned.