Sexually Transmitted Infections/Diseases

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Sexually Transmitted Infections/Diseases



History is replete with incidents of sexually transmitted diseases/infections (STDs/STIs). Virtually every major civilization and culture has recorded its experiences with sexually transmitted diseases and the effects they have had. In ancient Babylonia it was thought that sexually transmitted diseases were punishments enacted by the gods of love and fertility. In Hammurabi’s code there was a specific warning that anyone who opposed him would suffer an “evil disease” that would produce dangerous sores that could not be cured, a disease that physicians could not diagnose, would destroy a person’s seed, eliminating the chance to produce future offspring, and one that would inevitably lead to death—a description that perfectly fits STDs.

In more recent history we can see that STIs involve all aspects of a society. The notorious gangster of the 1920s, Al Capone, was able to escape the best efforts of law enforcement to put him away forever for his crimes. Although they finally were able to imprison him on charges of tax evasion, it appeared to many that he was going to escape judgment for his most serious crimes, until biology became the new prosecutor. Capone had contracted syphilis, which acted as judge and executioner, killing him in 1947.


One need not look far in national and international news to see headlines about STIs. The disease that has probably received the most attention in the past few decades is AIDS. The serious problems in dealing with the epidemic, especially in the African nations, have drawn the attention of the world. The United Nations and the United States have committed an enormous amount of money and support to help these nations, which are struggling to survive under the scourge of this sexually transmitted disease. Today AIDS is not limited to the African continent or to third-world nations, but continues to spread and claim lives in virtually every corner of the world and every level of society. Another disease that continues to hold its own is chlamydia, as it is one of most frequently found STIs in the United States. Although curable with antibiotics, many infected individuals do not display obvious symptoms, facilitating the spread of chlamydia. Chlamydia is also a disease that can weaken the body and allow it to become more susceptible to other, more serious STIs. And then there is gonorrhea; the use of oral contraceptives has become commonplace in today’s society, and it has been discovered that women using the birth control pill are actually more susceptible to gonorrhea because of chemical changes produced in the body by “the pill.”


Sexually transmitted infections/diseases (STIs/STDs) affect the same organs as the organs and structures covered in Chapter 16 (Infections of the Reproductive System). While affecting the same anatomical structures, the primary difference between infections of the reproductive system and sexually transmitted infections is the method of transmission. Sexual intercourse or any other sexual activity can lead to STIs, and eventually to STDs. Although the terms sexually transmitted infection and sexually transmitted disease are often used interchangeably, there is a distinction between the two. The term infection refers to just that, the presence of pathogenic organisms in a host, and symptoms of infection may be completely absent. The term disease refers to the appearance of symptoms and damaging effects as a result of an infection (see Chapter 9, Infection and Disease).

For the purpose of simplicity, STIs and STDs are referred to as STIs throughout this chapter. The organs that are affected by STIs in females are the ovaries, fallopian tubes, uterus, vagina, and external genitalia. In males the affected organs include the testes, prostate gland, urethra, and penis. Although reproductive organs are the primary targets, STIs may affect other organ systems and cause systemic problems. One of the likely reasons that sexual activity can lead to a high probability of STI transmission is the fact that most areas of the reproductive system are lined with mucous membranes, which are more susceptible to the penetration of pathogens than the skin (see Chapter 20, The Immune System). STIs can be caused by a variety of organisms including bacteria, fungi, viruses, and protozoa.

Bacterial Infections

Bacterial STIs include chlamydia, gonorrhea, syphilis, chancroid, and others. Most of these infections are treatable with antibiotics. However, with any of the bacterial STIs, when not diagnosed and treated early, significant problems including infertility may occur. Some strains of the bacteria causing STIs have also become resistant to certain antibiotics.


Gonorrhea is the most reported STI in the United States.* The infection is caused by the bacterium Neisseria gonorrhoeae, a gram-negative diplococcus, and humans are the only known natural host. Once thought to be rather fragile and fastidious, not surviving for long periods of time outside of the host, research has recently discovered strains that are capable of surviving in dried pus on a bed sheet for 6 weeks. The organism can be transmitted through vaginal, anal, and oral sexual activity. The typical incubation time for the infection is between 2 and 7 days. Gonorrhea can be transmitted by individuals who are asymptomatic. Up to 40% of males and between 60% and 80% of females may be infected without any symptoms, but they can act as carriers for up to 5 to 15 years. A small number of organisms, in some cases only about 1000, is required to cause an infection. The symptoms of gonorrhea vary between males and females (Box 17.1). Besides infections of the genitals, oral and anal sexual activity can also lead to gonorrheal infections in the pharynx and the rectum, leading to general systemic bacteremia. Symptoms of systemic gonorrheal infections include the following:

Gonorrhea increases the risks of other infections, including HIV and chlamydia. Men with prolonged infections may also develop an inflammation of the testicles called epididymitis, a condition often leading to infertility. Prolonged infections in women can result in pelvic inflammatory disease (see Chapter 16, Infections of the Reproductive System), which may include the uterus and fallopian tubes. Scar tissue in the fallopian tubes can prevent fertilization, and damage to the uterine wall can stop implantation of a fertilized ovum (zygote). Pelvic inflammatory disease also increases the risk of ectopic pregnancy.

During delivery gonorrhea can be passed from the infected mother to the baby as it moves through the birth canal (see Chapter 23, Human Age and Microorganisms). Infection of the newborn often leads to infection of the joints, blood infection (bacteremia), and/or blindness.

Diagnosis of gonorrhea is accomplished by identifying the organism by microscopic examination of discharge samples or in laboratory cultures of swabs from infected tissue. Treatment of gonorrhea originally involved sulfonamides and/or penicillin, but the organism has developed resistance to these antibiotics. Antibiotics currently used include ciprofloxacin, cefixime, ofloxacin, and levofloxacin.

Although treatment with antibiotics has a high success rate in eliminating the infection, any damage done to the organs during the infection is permanent.

At the present time there is no vaccine for gonorrhea but research is underway. Preventive measures to avoid contracting an infection include the following:


Syphilis has been in the human population for many years and is documented in many historical writings. Because it causes symptoms that can be associated with numerous other diseases, syphilis is sometimes referred to as the “great imitator.” It is caused by Treponema pallidum, a gram-negative spirochete. Humans are the organism’s only natural reservoir and transmission occurs through direct contact with sores of an infected person. Although the bacterium can be passed on through body fluids such as saliva, the primary means of transmission is through any sexual activity—vaginal, anal, or oral. A pregnant woman can also pass the infection on to her child during pregnancy. This infection is known as congenital syphilis (see Chapter 23, Human Age and Microorganisms).

Syphilis takes place in three stages, with an incubation time between 10 and 90 days after the initial infection. The initial symptoms may be mild and are sometimes difficult to diagnose because they resemble symptoms of other diseases such as gonorrhea. Many infected persons in the early stages do not realize that they are infected. If treated early, syphilis can be cured without any resulting serious or long-term health problems. Untreated, syphilis manifests itself in three stages: primary, secondary, and tertiary syphilis (Table 17.1).

TABLE 17.1

Stages of Syphilis

Stage Time Frame Symptoms
Primary Ten to 90 d after initial infection Small, red skin sores
Secondary Two to 10 wk after primary stage Red-brown rash on palms of hands and soles of feet; fever, swollen lymph nodes, sore throat, muscle and joint pain, loss of patches of hair, malaise, rash on skin and mucous membranes of mouth, throat, and cervix
Latent After secondary stage None
Tertiary Many years from onset of the latent phase Gummas—rubbery masses of tissue in various organs; memory loss, ataxia, paralysis, insanity, and finally death

• Primary syphilis represents itself as small, red sores (chancres) that appear on the body at the site of infection within 10 to 90 days after initial contact. These sores will eventually disappear, leaving a scar on the skin. if untreated, the symptoms will move to the secondary stage.

• Secondary syphilis occurs within 2 to 10 weeks of the primary stage (Figure 17.2). During this stage the organism enters the bloodstream and travels to other organ systems, causing a wide variety of symptoms including the following:

Without treatment at this point the disease will move into the tertiary stage:

Patients with syphilis in the later stages are also at increased risk for HIV infection.

Pregnant women run the risk of passing the infection on to their unborn child and they have an increased risk for miscarriage, premature delivery, and stillbirth (see Chapter 23, Human Age and Microorganisms). Diagnosis of syphilis can be done by a number of different methods. Observing a sample from a lesion for the organism itself, using a dark-field microscope, is typically one of the first methods used for early detection. Along with microscopic examination, a number of blood-screening tests are available to confirm an infection. These include the following:

Because of the possibility that a single test may result in a false positive or negative reading during the different stages of the disease or under different circumstances, at least two blood tests are done to determine and confirm an infection. For example, the tests based on detection of antibodies are not useful in diagnosing the infection in a person who has had the disease previously, as the antibodies remain in the body for years.

Treatment for syphilis in the primary and secondary stages is fairly simple and can often be achieved with a single intramuscular dose of penicillin. In a more advanced stage of the infection hospitalization and a daily antibiotic regimen may be required. Tetracycline and erythromycin have proven to be effective for persons allergic to penicillin. At the present time there is no vaccine available; however, research is ongoing. Preventive measures to avoid contracting syphilis include the following:


Although usually referred to simply as chlamydia, the organism Chlamydia trachomatis, a gram-negative coccus and an intracellular obligate parasite, is responsible for a number of different infections of the reproductive system. These include nongonococcal urethritis (NGU), pelvic inflammatory disease (PID), and lymphogranuloma venereum (LGV). Chlamydial infections are now the most prevalent STIs in the United States (Box 17.2). Female carriers of the infection are often asymptomatic, thus increasing the transmission of chlamydial infections. Transmission occurs through exchange of semen or vaginal fluid during vaginal, oral, or anal sexual activity. Pregnant women can also pass the infection on to their child during labor and delivery. The incubation period is between 1 and 3 weeks before symptoms appear. The symptoms of a chlamydial infection tend to be very mild or virtually nonexistent. According to research data, up to 75% to 80% of infected women and up to 50% of infected men show no symptoms at all.