their patients regarding STDs as discussed in Chapter 3. Many sexually transmitted infections can persist for years without evidence of infection until life-threatening complications are recognized. In particular, viral STDs often result in lifelong infection for which there is currently no curative treatment. The serious long-term complications of STDs affecting millions of women, infants, and men in the United States each year are summarized in Table 2-3.

Cancers Caused by STDs

Several sexually transmitted pathogens cause cancer. The direct role of STDs in causing genital cancers has been largely unrecognized. Certain types of sexually acquired human papillomavirus are now considered to be a cause of most cancers of the cervix, vagina, vulva, anus, and penis. Hepatitis B virus, which is usually transmitted either by sexual contact or by intravenous drug use among adults in the United States, is a cause of hepatocellular carcinoma, one of the world's most common forms of cancer. Human T-cell lymphotrophic virus type I (HTLV-I), sexually transmitted among adults and transmitted to infants especially by breast-feeding, causes certain malignancies, including T-cell leukemia and lymphoma. Human herpes virus type 8 (HHV8) is a newly discovered virus, probably sexually transmitted, that may cause Kaposi's sarcoma and certain forms of lymphoma. Epstein-Barr virus (EBV), transmitted among adults by intimate contact, including kissing and sexual intercourse, is associated with other types of lymphoma and with nasopharyngeal (nasal cavity and pharynx) carcinoma.

Cervical Cancer

Carcinoma of the uterine cervix, particularly among women of reproductive age, is now known to be strongly associated with certain oncogenic types of human papillomavirus (NIH, 1996). Of more than 70 types of human papillomavirus that have been identified, several oncogenic forms, such as types 16, 18, 31, and 45, have the strongest association with cervical cancer. Both biological and epidemiological data suggest that human papillomavirus is a dominant etiologic factor for cervical cancer. Studies show that cervical infection with oncogenic types of human papillomavirus is associated with at least 80 percent of invasive cervical cancer cases (NIH, 1996) and that women with human papillomavirus infection of the cervix are 10 times more likely to develop invasive cervical cancer compared to women without human papillomavirus infection (Schiffman, 1992).

Much of the cervical cancer burden related to human papillomavirus infection may be averted by preventing high-risk sexual behaviors (Brinton, 1992), especially avoiding unprotected sex with multiple male partners, some of whom may have chronic genital infection with oncogenic human papillomavirus types. Screening with the Pap smear is currently the best available method for reducing

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