HUMAN BIOLOGY

322 Chapter 16

stds Caused by viruses and parasites

Genital herpes is a lifelong infection

Like HIV infections (Section 9.10), herpes virus infections

are extremely contagious. Herpes simplex is transmitted by

contact with active viruses or sores that contain them (Fig-

ure 16.18A). Mucous membranes of the mouth or genitals

and broken or damaged skin are most susceptible.

In 2005 the National Institutes of Health estimated that

in the United States, one in five people over the age of

12—roughly 45 million people—have one of the two viral

strains that cause genital herpes. Type 1 strains infect

mainly the lips, tongue, mouth, and eyes. Type 2 strains

cause most genital infections.

Symptoms usually develop within 2 weeks after infection,

although sometimes they are mild or absent. Usually, small,

painful blisters erupt on the penis, vulva, cervix, urethra, or

around the anus. The sores can also occur on the buttocks,

thighs, or back. The first flare-up may cause brief flulike

symptoms. Within 3 weeks the sores crust over and heal.

Every so often the virus may be reactivated. Then it

produces new, painful sores at or near the original site of

infection. Recurrences can be triggered by stress, sexual

intercourse, menstruation, a rise in body temperature, or

other infections.

There is no cure for herpes. Between flare-ups, the virus

simply is latent in nervous tissue. However, several antivi-

ral drugs inhibit its ability to reproduce. They also reduce

the shedding of virus particles from sores, and sores are

often less painful and heal faster.

Human papillomavirus can lead to cancer

Worldwide, an estimated 20 million people become infected

with the human papillomavirus (HPV) each year (Table

16.5). One form of HPV causes growths called genital

warts, which can develop months or years after a person

is exposed to the virus. Usually they occur in clusters on

the penis, the cervix, or around the anus (Figure 16.18B).

Certain forms of HPV cause most cases of invasive cer-

vical cancer, as well as some anal and oral cancers. Any

woman having a history of genital warts should tell her

physician, who may recommend an annual Pap smear—a

test for abnormal growth of cervix cells. Several years ago

an anti-HPV vaccine became available, and the Centers for

Disease Control recommends that both girls and boys (who

can transmit the virus) be vaccinated before they become

sexually active.

Hepatitis can be sexually transmitted

Two types of hepatitis can be transmitted through sex. Like

HIV, the hepatitis B virus (HBV) is transmitted in blood or

body fluids such as saliva, vaginal secretions, and semen.

However, HBV is far more contagious than HIV. The num-

ber of sexually transmitted cases is growing; in the United

States about 80,000 new cases are reported each year. The

virus attacks the liver. A key symptom is jaundice, yellow-

ing of the skin and whites of the eyes as the liver loses its

ability to process bilirubin pigments produced when liver

cells break down hemoglobin from red blood cells. In some

cases the infection becomes chronic and can lead to liver

cirrhosis or cancer. The only treatment is rest. However,

people at known risk for getting the disease (such as health

care workers and anyone who requires repeated blood

transfusions) can be vaccinated against HBV.

The hepatitis C virus (HCV) causes liver cirrhosis and

sometimes cancer. It is carried in the blood and can reside

in the body for years before symptoms develop. A blood-

borne disease, HCV can be transmitted sexually if con-

taminated blood enters a sex partner’s body through cut or

torn skin.

Figure 16.18 Viruses cause herpes and genital warts.

A Herpes lesion on the buttocks. B Genital warts caused

by HPV (human papillomavirus). (Dr. P. Marazzi/Science Source)

16.10

A

B

STD U.S. Cases Global Cases

HPV infection 5,500,000 20,000,000

Trichomoniasis 5,000,000 174,000,000

Chlamydia 3,000,000 92,000,000

Genital herpes 1,000,000 20,000,000

Gonorrhea 650,000 62,000,000

Syphilis 70,000 12,000,000

AIDS 40,000 4,900,000

Table 16.5 New STD Cases Annually*

*Global data on HPV and genital herpes were last compiled in 1997.

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