HUMAN BIOLOGY

320 Chapter 16

some Common sexually transmitted diseases

enlarged and tender. Impaired lymph drainage can cause

swelling in the surrounding tissues.

Chlamydia can be treated with antibiotics. However,

because so many people are unaware they’re infected, this

STD does a lot of damage. Between 20 and 40 percent of

women with genital chlamydial infections develop pelvic

inflammatory disease (PID). PID strikes about 1 million

women each year, most often sexually active women in

their teens and twenties.

Although PID can arise when microorganisms that nor-

mally inhabit the vagina ascend into the pelvic region (typ-

ically as a result of too much douching), it is also a serious

complication of both chlamydia and gonorrhea. Usually, a

woman’s uterus, oviducts, and ovaries are affected. Pain

may be so severe that infected women often think they

are having an attack of acute appendicitis. If the oviducts

become scarred, additional complications, such as chronic

pelvic pain and even sterility, can result. PID is the lead-

ing cause of infertility among young women. An affected

woman may also develop chronic menstrual problems.

As soon as PID is diagnosed, a woman usually will be

prescribed antibiotics. Advanced cases can require removal

Chlamydia infections and pid are most

common in young sexually active people

One of the most common sexually transmitted diseases

(STDs) is caused by the bacterium Chlamydia trachomatis

(Figure 16.16A and Table 16.4). This infection is often simply

called chlamydia. Each year an estimated 3 million Ameri-

cans are infected, about two-thirds of them under age 25.

Around the world, C. trachomatis infects roughly 90 million

people annually. At least 30 percent of newborns who are

treated for eye infections and pneumonia were infected

with C. trachomatis during birth.

The bacterium infects cells of the genital and urinary

tract. Infected men may have a discharge from the penis

and a burning sensation when they urinate. Women may

have a vaginal discharge as well as burning and itching.

Often, however, C. trachomatis is a “stealth” STD with no

outward signs of infection. About 80 percent of infected

women and 40 percent of infected men don’t have obvious

symptoms—yet they can still pass the bacterium to others.

Once a bout of chlamydia is under way, the bacteria

will migrate to the person’s lymph nodes, which become

16.9

Figure 16.16 Chlamydia, gonorrhea, and syphilis all are caused by bacteria. A Color-enhanced micrograph of Chlamydia trachomatis

bacteria. B Neisseria gonorrhoeae, or gonococcus, a bacterium that typically is seen as paired cells, as shown here. C Syphilis bacteria

(dark squiggles) in an infected testicle.

B

CNRI/Science Source

A

David M. Phillips/Science Source

C

Michael Abbey/Science Source

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).