Human Papillomavirus.

What Are HPV 16 and 18?

HPV is the abbreviation for human papillomavirus. It is a very common virus that is spread through sexual contact. HPV has many different strains (or types), and the various types are distinguished by numbers. HPV 16 and 18 are well known because they have been shown to significantly increase the risk of cervical cancer in women who have persistent infections with these two types of HPV.

Infection with HPV is very common among sexually active women. However, in most women such infections are transient, since the HPV-infected cells are shed from the cervix. In a minority of women, though, the HPV persists, and if the persistent HPV is type 16 or 18, there is a marked increase in the risk of developing cervical cancer.

Fortunately, the time from infection with a high-risk HPV type to the development of cervical cancer is generally measured in years. Such slow growth allows certain precancerous changes in the cervical cells to be found on screening Pap smears. Dysplasia, an abnormal growth or development of cells, is one such type of precancerous change. Now that there is a simple test to look for HPV 16 and 18 in the cervical cells, doctors can test a "dysplasia" Pap smear for the presence of either type of HPV. If HPV 16 or 18 is found, it means that the dysplasia carries a higher risk of becoming a cancer. In such a case, appropriate treatment of the dysplasia, further workup to rule out cancer, or a closer follow-up may be recommended.

Incubation

The incubation period for HPV 16 to give rise to cervical cancer is quite long and rather variable.  It has been estimated that among HPV 16-positive women, the median incubation period from first detected HPV infection to cervical carcinoma in situ was between 7 and 12 years.

Epidemiology

HPV is one of the most common STDs among sexually active young people. The CDC estimates that 20 million people in the US are infected with HPV 16 and that every year, there are about 5.5 million new infections.

A study by the CDC on prevalence of HPV 16 in the US showed that the prevalence of HPV-16 was at least two-fold higher in women compared to men. Women of all races had an HPV-16 prevalence of 17.9 percent, compared to 8 percent for men. African-American women age 20 to 29 had the highest prevalence of HPV-16 at 36 percent. African Americans overall had 19.1 percent prevalence, compared to 12.5 percent in whites. The prevalence of HPV-16 was higher in study participants who had a larger number of lifetime sex partners. 7 percent of people with one lifetime sex partner had the infection compared to 20.1 percent of people with 50 or more lifetime sex partners. Overall, thirteen percent of the study population carried HPV-16 antibodies. However, the figure does not represent all people in the study with the infection because not all people who have been infected develop detectable antibodies.

Symptomatology and Outcome

HPV-16 is the biggest causative agent of cervical cancer. It can also causes vulvar, anal, vaginal, and penile cancer, as well as vaginal intraepithelial neoplasia, anal intraepithelial neoplasia, vulvar intraepithelial neoplasia, and penile intraemithelial neoplasia. Neoplasia is the pathological process that results in the formation and growth of a tumor.  Intraepithelial neoplasia of the various described organs is simply neoplasia in the epithelial cells.

Prevention and Management

         HPV 16 is transmitted through sexual contact with an infected person.  The only full-proof way of protecting against HPV 16 infection is by practicing abstinence. Having a monogamous relationship with one sexual partner known to be disease-free helps to prevent infection. The HPV types that cause cervical cancer are sexually transmitted, but there is little evidence that infection can be avoided by behavioral change, such as condom use. Nonetheless, condoms should still be used. They reduce your chances of getting or spreading STDs. Prophylactic vaccines against HPV infection are likely to have high efficacy, but are not yet available for use.

         The Pap test is a screening test for detecting abnormal changes in the cells of the cervix. The test involves taking a small sample of cells from the cervix during a routine pelvic exam. The cells are then prepared and evaluated under a microscope to look for nuclear atypia, atypical mitotic figures, and cellular disorganization.

         Since the popularization of the pap smear, cell abnormalities that may lead to cervical cancer have been discovered earlier and thus treated earlier, resulting in a drop in morbidity and mortality from cervical cancer in the US. There was a 28% decrease in the incidence rate of cervical cancer between 1982 and 1997, and a 47% decrease in the death rate from cervical cancer between 1982 and 1997.

         The rate of cervical cancer is higher in women 40 years and older than in younger women. However, the good news is that cervical intraepithelial neoplasia, the precursor lesion to cervical cancer, most often occurs among young women, and thus can be caught early to prevent progression to cervical cancer. Cervical cancer is preventable and curable if it is detected early. There is currently no treatment available for the virus itself.  However, good treatments do exist for the problems HPV can cause, such as cervical cell changes or genital warts.

(sources:everydayhealth.com  and stanford.edu)

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