Pathogenesis

HPVs are thought to enter and infect the deeper layers of epithelium through microscopic abrasions. A latent infection, without warts or microscopic lesions, is the most common result of infection. Latent infection can last for years, but studies in college age women reveal that about 90% of HPV infections are eliminated by body defenses within 2 years. Viral replication and

Nester-Anderson-Roberts: I IV. Infectious Diseases I 25. Genitourinary I I © The McGraw-Hill

Microbiology, A Human Infections Companies, 2003

Perspective, Fourth Edition

Figure 25.19 Abnormal Papanicolaou Smear The pink and blue objects are squamous epithelial cells; abnormalities include doubling of the nuclei and a clear area around them. Most abnormal smears in young women are due to human papillomavirus infection, when persistent an important factor in the development of cancer of the cervix.

Figure 25.19 Abnormal Papanicolaou Smear The pink and blue objects are squamous epithelial cells; abnormalities include doubling of the nuclei and a clear area around them. Most abnormal smears in young women are due to human papillomavirus infection, when persistent an important factor in the development of cancer of the cervix.

release are intermittent and require that the deeper layer of epithelial cells enter a maturation process. Different kinds of lesions develop depending on the virus type and the location of the infection. Lesions can be flat, raised or unraised, cauliflower-like, or hidden within the epithelium.

The mechanism giving rise to warts is unknown. The viral genome exists in infected cells as extrachromosomal closed DNA circles. Warts usually appear about 3 months after infection (range, 3 weeks to 8 months). Following removal or destruction of warts, HPV persists in surrounding normal-appearing epithelium and can give rise to additional warts. Warts can occasionally partly obstruct the urethra or, if very large, the birth canal. Newborn infants can become infected with HPV at birth and develop warts that obstruct their respiratory tract, a serious condition that occurs in less than one out of every 100,000 births.

Worldwide, cancer of the cervix is second in frequency only to breast cancer among the malignant tumors of women. In the United States, about 5,000 women die of cervical cancer each year. Most of these cancers are associated with certain HPV types. Cancer-associated HPV types differ from wart-causing HPV types in that the former can integrate into the chromosome of a host cell and code for a protein that permits excessive cell growth. These oncogenic types of HPV tend to cause infections that persist longer than other HPV types, and to cause precancerous lesions. A cancer-associated HPV is present in almost all cervical cancers, but only a small percentage of infections by these viruses result in cancer. This indicates that other unknown factors must be present for cancer to develop. Cervical cancer-associated HPVs have also been found in vaginal cancers, cancers of the penis, and in anal cancers of men and women who engage in receptive anal intercourse.

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