What are sexually transmitted diseases (STDs)?

Causes and Symptoms

Sexually transmitted diseases, or STDs (formerly called venereal diseases), have plagued humankind for centuries. The most prevalent, serious STDs are syphilis, gonorrhea, nongonococcal urethritis, trichomoniasis, genital herpes, genital warts, viral hepatitis, and AIDS. Others, troublesome but not as serious, include lice, scabies, and vaginal yeast infections. They are passed on from one person to another mostly by sexual contact, although some of these diseases may be acquired indirectly through contaminated objects or blood. In addition, nearly all these diseases can be passed on from an infected mother to her fetus, which may cause birth defects, severe and damaging infections, or even death. A person can acquire several STDs at the same time, and since recovery from an STD does not confer immunity, a person can get them again and again. Many of these diseases are asymptomatic, which allows them to spread and cause serious complications before a victim is aware of being infected. Finally, some STDs are treatable and some are not.

Syphilis is caused by Treponema pallidum. This bacterium normally infects the penis in males and the vagina or cervix in females, but it can also enter through a cut on the mouth or other parts of the skin. Once inside, the bacteria grow at the site of entry, then spread throughout the body through the lymph and blood vessels. The symptoms of syphilis are caused by the efforts of the immune response of the patient to fight off the infection. The disease occurs in three stages: primary, secondary, and tertiary. In primary syphilis, a flat, firm, painless, red sore called a chancre appears at the site of entry two to ten weeks after infection. Secondary syphilis is characterized by a red rash that appears two to ten weeks after the disappearance of the primary lesion. The rash will disappear in a few weeks. Without treatment, 40 percent of patients will progress to the tertiary stage within three to ten years. Tertiary syphilis is characterized by the formation of severe lesions called gummas on the skin, bones, or internal organs. Gummas on the spinal cord, brain, or heart can lead to seizures, insanity, or death. Almost all pregnant women with untreated primary or secondary syphilis will transmit the bacteria through the placenta to the developing baby, who will develop congenital syphilis. Many babies with congenital syphilis are spontaneously aborted or stillborn. Many others are born with characteristic birth defects, secondary or tertiary syphilis, or neurological damage, and may die shortly after birth.

Gonorrhea is caused by the Neisseria gonorrhoeae bacterium (also known as gonococcus). The bacterium infects the urethra in males and the cervix, vagina, or urethra in females. Most infected males get urethritis (inflammation of the urethra) along with symptoms of a pus-containing discharge from the penis and painful urination. Untreated, 1 percent of these men will develop complications of urethral blockage, epididymitis (inflammation of the epididymis, a sac through which sperm passes as it leaves the testicles), prostatitis (inflammation of the prostate, a gland that secretes fluid for semen), and infertility. Between 20 and 80 percent of women infected with gonococcus are asymptomatic or show only mild symptoms. Symptoms include burning or high frequency of urination, vaginal discharge, fever, and abdominal pain. In 20 to 30 percent of untreated women, gonococcus will spread to the Fallopian tubes and cause pelvic inflammatory disease (PID), which can lead to infertility. Infected mothers can transmit the bacteria to their babies as they pass through the birth canal, causing ophthalmia neonatorum, a type of conjunctivitis (inflammation of the eye) that can cause blindness if untreated.

Most cases of nongonococcal urethritis (NGU) are caused by Chlamydia trachomatis types d through k. This bacterium infects the urethra in males and the cervix or urethra in females. The symptoms of chlamydia infection are often mild and go unnoticed. Males experience mild urethritis with a watery discharge, frequent urination, and painful urination. Females are either asymptomatic or experience mild cervicitis (inflammation of the cervix) or urethritis. Complications include epididymitis in males and PID and infertility in females. Infants born to mothers with cervicitis can develop eye (inclusion conjunctivitis) or lung (infant pneumonia) infections.

Trichomoniasis is caused by the protozoan Trichomonas vaginalis. In both sexes, the disease is often mild or asymptomatic. In males, the organism infects the prostate, seminal vesicles, and urethra. About 10 percent of infected males show signs of mild urethritis, with a thin, white urethral discharge. Secondary bacterial infection can lead to more severe urethritis and inflammation of the prostate and seminal vesicles. In females, the organism can infect the vulva, vagina, and cervix. Females may suffer from severe vaginitis, which includes a tender, red, and itchy genital area, and a profuse, frothy, foul-smelling, greenish-yellow discharge. Newborns may acquire the infection from an infected mother during delivery.

Most genital herpes infections are caused by herpes simplex virus type 2, but some are caused by herpes simplex virus type 1. The virus infects the penis in males and the cervix, vulva, vagina, or perineum in females. Two to seven days after infection, painful blisters appear in the genital area that ulcerate, crust over, and disappear in a few weeks. Herpes viruses are unique in that they can remain latent in the nerves and cause a recurrent infection at any time in the future. Fever, stress, sunlight, or local trauma may trigger the virus to come out of hiding and cause a recurrent infection. The virus can be transmitted from an infected mother to her baby either congenitally, through the placenta, or neonatally, as the baby passes through the birth canal. In congenital or neonatal herpes, the virus can infect all parts of the body, the death rate is high, and survivors commonly have long-term neurological damage and recurrent infections.

Viral hepatitis is also an STD. At least three variants of the virus—hepatitis A virus (HAV), HBV, and HCV—are known to be transmitted sexually. HBV is the form most commonly transmitted sexually. Vaccines are available to immunize persons at risk for HAV and HBV.

Genital warts are caused by human papillomaviruses (HPVs). In males, the warts appear on the penis, anus, and perineum. They are found on the vagina, cervix, perineum, and anus in females. The warts themselves may be removed, but the infection remains for the life of the patient. HPV infection seems to increase a woman’s risk for cervical cancer. Two vaccines for HPV, Gardasil and Cervarix, are now available.

AIDS is caused by the human immunodeficiency virus (HIV). This virus is acquired through sexual contact as well as through intravenous drug use and blood transfusions. HIV infects and inactivates the T helper cells that are needed by the immune system to respond to and fight off infections. Without T helper cells, the immune system eventually becomes nonfunctional, and the affected person becomes susceptible to every type of infection possible. Two-thirds of all AIDS patients get pneumonia caused by Pneumocystis carinii. Other common diseases associated with AIDS patients are tuberculosis and other mycobacterial infections; viral infections such as those caused by cytomegalovirus and herpes viruses; fungal infections; cancers such as Kaposi’s sarcoma; and neurological disorders. HIV can also be transmitted from an infected mother to her baby through the placenta.

Treatment and Therapy

Sexually transmitted diseases can be diagnosed in several ways. One way is by observing the symptoms and case history of the patient. Characteristic sores or symptoms can lead a doctor to suspect a particular disease, and a sample of a scraping from a lesion or an unusual discharge can be examined under a microscope to identify the infecting organism. The syphilis, gonorrhea, chlamydia, and trichomoniasis organisms all have unique shapes that a doctor can recognize. For those STDs with mild symptoms or no symptoms, a doctor can try to grow the organism in the laboratory from samples taken from appropriate sites on the body. All organisms that cause STDs can be grown in the laboratory, and since these organisms are not normally present in humans, isolation of the organism from the body is a sign that the body has been infected by that organism. Finally, there are many blood tests that have been developed to test whether a person has specific antibodies in his or her blood that bind to one of these organisms. The presence of antibodies to an organism implies that one has been or is currently infected with that organism. In many cases, doctors will use several of these methods to confirm a diagnosis of an STD.

Specific treatment recommendations for each sexually transmitted disease are subject to periodic revision. Current recommendations are reviewed by the Centers for Disease Control and are published in the Morbidity and Mortality Weekly Report every three or four years. It is important for physicians to review these recommendations in order to prescribe the best method for treating STDs. All the bacterial and the protozoal STDs can be treated and cured with antibiotics. It is important to seek early diagnosis and treatment of these diseases for three reasons: first, to prevent the disease from spreading; second, to prevent the various complications associated with the diseases; and third, to prevent the infection of infants by pregnant mothers. There is no cure for STDs caused by viruses; there are only drugs that slow the progress of the infection.

Syphilis is commonly treated with penicillin, or alternatively with erythromycin, doxycycline, or ceftriaxone. In most patients receiving appropriate therapy during primary or secondary syphilis, the active disease is totally and permanently arrested. Treatment during the latent stage stops the development of symptoms of the tertiary stage. There is no successful treatment for patients with tertiary syphilis. Cephalosporin antibiotics, such as cefixime and ceftriaxone, have replaced penicillins as therapeutic agents for gonorrhea because of widespread resistance of gonococci to penicillins. Quinolones, such as ciprofloxacin, and azithromycin are other antibiotics that can be effective treatment for gonococcal infections. Doxycycline or azithromycin are used to treat NGU caused by chlamydia, and trichomoniasis is treated with metronidazole or tinidazole.

Genital herpes is treated with antiviral agents such as acyclovir. Topical application of acyclovir is helpful in reducing the duration of primary, but not recurrent, infections. The use of oral acyclovir to suppress recurrent infections may cause more severe and more frequent infections once the therapy has stopped. Neonatal herpes is treated with acyclovir or vidarabine, which can reduce the severity of the infection but cannot reverse any herpes-related neurological damage or prevent recurrent infections. Genital warts can be removed by chemicals, freezing, electrocautery, or laser therapy. Antiviral drugs are useful in treating some STDs: acyclovir for genital herpes, zidovudine for AIDS, and interferon for hepatitis virus. They slow the progress of the disease in some persons, but they do not cure it.

As with any disease, prevention is the most desirable means of controlling STDs. With the exception of viral hepatitis and HPV, there are no vaccines for STDs; although much research is being done and many potential vaccines have been developed and tested, none is yet satisfactory for general and routine use. Therefore, behaviors resulting in disease avoidance are the only means of preventing most STDs. The only 100 percent effective way to prevent a sexually transmitted disease is abstinence. Abstinence means to refrain voluntarily from engaging in sexual activity. Since many of these diseases can be spread through sexual activity other than intercourse, abstinence must include all sexual activity. Choosing to exercise one’s sexuality within a monogamous relationship for life can also help prevent sexually transmitted disease. The use of a condom or any other barrier method can significantly reduce the risk of STD transmission, but is not always effective. Prevention of transmission of STDs from infected mothers to their babies involves early diagnosis and treatment of the mothers before birth and preventive medication of the babies after birth. In the past, ophthalmia neonatorum was the cause of blindness for half of the children admitted to schools for the blind. Therefore, the government made it mandatory to treat all newborns’ eyes with silver nitrate, tetracycline, or erythromycin, to prevent this disease. The instillation of silver nitrate in babies’ eyes does not prevent chlamydia eye infections, so babies born to mothers with chlamydia need additional antibiotic treatment. Prevention of neonatal herpes may involve delivery by cesarean section to avoid infection of the child as it passes through the birth canal. Preventing the spread of AIDS includes screening blood supplies, organ donors, and semen donors and avoiding contact with infected body fluids through sexual contact, blood transfusions, or intravenous drug use.

Control of STDs in a population is complex, since it is both a medical and a social problem. First, it is important that persons who contract a sexually transmitted disease receive early diagnosis and adequate treatment that will prevent further spread of the disease, serious complications, and infection of infants. This is difficult because many STDs are asymptomatic; therefore, people do not know they have the disease and have no reason to seek treatment. Many persons contract STDs from asymptomatic carriers. In addition, social stigma or embarrassment reduces the motivation of a victim to seek prompt medical care. Adequate treatment of STD victims is difficult if they do not want to return for subsequent treatment or will not take all their prescriptions. Finally, people often contract several STDs at the same time, so detection of one STD should routinely instigate testing for other STDs.

Not only does the person with an STD need to be treated, but all the sexual contacts of that person need to be contacted, tested, and treated as well. Public health officials interview victims of STDs to determine the names and addresses of contacts and then try to find and treat the contacts. This is difficult if a victim does not remember who those contacts are, if he or she does not want to discuss his or her sexual activity, or if the contacts do not want to be bothered by the health department. In addition, many private physicians do not report cases of STDs to the public health department; therefore, in many cases, the sources of STDs are never interviewed.

A reduction in risky sexual behavior, such as unprotected sex, would aid in the control of STDs. Effective education to change sexual behavior must be predicated upon the motivation and cognitive development of the student. One-third of all cases involve teenagers and young adults; sexual activity in this age group is on the rise, and members of this group are more likely to have multiple sex partners. Prostitution for money or drugs also increases the incidence of STDs. Other control measures include development of vaccines for these diseases, mandatory reporting of all STDs, and education of the population regarding the dangers and risks involved in acquiring these diseases.

Perspective and Prospects

Syphilis was first recognized at the end of the fifteenth century in Europe, where it rapidly reached epidemic proportions and was called the “great pox.” Gonorrhea was described and given its present name by the Greek physician Galen in 150 CE From the fifteenth century to the eighteenth century, there was much confusion as to the nature of syphilis and gonorrhea, and many persons thought they were different stages of the same disease. In 1767, an English physician named John Hunter inoculated himself with a urethral discharge from a patient with gonorrhea in order to determine once and for all whether they were one disease or two. Unfortunately, that patient also had syphilis, so when Hunter developed symptoms of both gonorrhea and syphilis he concluded they were a single disease. It was not until 1838 that it was clearly proved that they were two separate diseases. Traditionally, 95 percent of all cases of sexually transmitted diseases were either syphilis or gonorrhea. Since the late twentieth century, however, there has been a dramatic increase in the incidence of several other sexually transmitted diseases, such as genital herpes, NGU, AIDS, genital warts, and trichomoniasis.

The rise in incidence of STDs is of epidemic proportions. The World Health Organization reports that in 2008 more than a million people worldwide contracted a sexually transmitted infection (STI) per day and that about 499 million new cases of curable STIs occurred per year. The WHO also reported that in 2011 there were about 34 million people living with HIV around the world; of these more than 8 million people were receiving anti-retroviral therapy (ART) in low- and middle-income nations. The international community set a goal of providing 15 million people with ART by 2015.

In the United States, the Centers for Disease Control and Prevention reported in 2013 that, based on 2008 data, there were a total of 110 million STI cases. About 19.7 million new cases of STIs occur annually, with people between the ages of fifteen and twenty-four accounting for roughly 50 percent of new cases. The direct medical costs related to STIs were estimated to be $16 billion (in 2010 dollars). By 2008, HPV had become the most frequently diagnosed STI in the United States, estimated at more than 14.1 million new cases annually. Other STIs with high incidence included chlamydia (2.86 million new cases annually), trichomoniasis (1.09 million annually), gonorrhea (820,000 new cases annually), and genital herpes (776,000). Because there is no cure for genital herpes, it may be present in 24.1 million Americans. By 2009, there were about 1.1 million people with HIV living in the United States. As of 2010, there were about 47,500 new cases of HIV and 15,500 AIDS-related deaths in the United States. It is estimated that there are 3 to 5 million new cases of NGU per year. One in five couples in the United States is infertile, and much of that infertility is caused by the complications associated with STDs, with chlamydial infection being the primary preventable cause of sterility in women. In the United States, it is estimated that 25 percent of all women are infected with trichomoniasis.

Despite the fact that most STDs can be controlled, the incidence of many of the diseases is still quite high; thus, STDs obviously present a social as well as a medical problem. An increase in education concerning the signs and risks of these diseases, a reduction in unprotected sex, and development of vaccines would help in controlling these destructive and fast-spreading diseases.

Bibliography

Berek, Jonathan S., ed. Berek and Novak’s Gynecology. 15th ed. Philadelphia: Lippincott Williams & Wilkins, 2012.

Biddle, Wayne. A Field Guide to Germs. 3d ed. New York: Anchor Books, 2010.

Centers for Disease Control and Prevention. CDC Fact Sheet: Incidence, Prevalence, and Cost of Sexually Transmitted Infections in the United States. Atlanta, Ga.: Centers for Disease Control and Prevention, February, 2013.

Centers for Disease Control and Prevention. "HIV/AIDS: Basic Statistics." Centers for Disease

Eng, Thomas Rand, and William T. Butler, eds. The Hidden Epidemic: Confronting Sexually Transmitted Diseases. Washington, D.C.: National Academy Press, 1997.

Larsen, Laura. Sexually Transmitted Diseases Sourcebook. 4th ed. Detroit, Mich.: Omnigraphics, 2009.

Little, Marjorie. Sexually Transmitted Diseases. Rev. ed. Philadelphia: Chelsea House, 2000.

MedlinePlus. "Sexually Transmitted Diseases." MedlinePlus, May 28, 2013.

Morse, Stephen A., Ronald C. Ballard, and King K. Holmes. Atlas of Sexually Transmitted Diseases and AIDS. 4th ed. [Edinburgh?]: Saunders/Elsevier, 2010.

Shaw, Michael, ed. Everything You Need to Know about Diseases. Springhouse, Pa.: Springhouse Press, 1996.

World Health Organization. "HIV/AIDS (Fact Sheet No. 360)." World Health Organization: Media Centre, November, 2012.

World Health Organization. Sexually Transmitted Infections (STIs). Geneva, Switzerland: 2013.