AIDS and HIV Infection

AIDS, acquired immunodeficiency (ih-myoo-no-dih-FIH-shen-see) syndrome, is the condition caused by infection with HIV, the human immunodeficiency virus. HIV attacks the body's immune system, leaving one susceptible to life-threatening illnesses. Spread primarily through unprotected sexual activity or needles contaminated with infected blood, HIV/AIDS had become a worldwide epidemic by the end of the 20th century.

In 1984, at the onset of the AIDS epidemic, Ryan White became infected with the HIV virus through a blood transfusion.

In 1984, at the onset of the AIDS epidemic, Ryan White became infected with the HIV virus through a blood transfusion. His spirited fight to educate the public about the disease and to end prejudice against people with AIDS ended with his death in 1990 at the age of 18.
Kim Komenich/Getty Images.

Carl's Family: How Could This Happen?

Carl could not have been more shocked when his mother informed him that she was HIV positive. After all, she worked full time, kept house, volunteered at church, and was raising Carl alone. Ever since Carl's father had died of brain cancer, she had not even been out on a date. And she was the last person in the world he could imagine shooting up drugs. How could she have contracted HIV? But Carl had not been told the whole story of his father's death. Yes, it had been cancer, but it was a type of cancer—lymphoma of the brain—that strikes HIV-infected people. Carl's father had died of AIDS.

How Did the AIDS Epidemic Begin?

AIDS was first described in the United States in 1981, when gay men in California and New York began developing unusual infections and cancers, similar to illnesses in children born with weak immune systems. However, as early as 1978 cases of what would later be called AIDS were showing up in gay men in the United States and Sweden, and in heterosexuals in Tanzania and Haiti. In Africa and the Caribbean, AIDS appeared to be spread primarily through heterosexual contact, and sometimes babies were born with it. AIDS also seemed to strike people who had received blood transfusions, and drug addicts who shared needles. HIV was identified as the causative agent of AIDS in 1983, the same year that the Centers for Disease Control and Prevention (CDC) warned that the blood supply might be at risk. Within just a few years, HIV/AIDS had become one of the worst epidemics in human history.



HIV is a retrovirus that attacks the human immune system * by disabling and destroying a type of white blood cell called a CD4-positive (CD4+) T-cell or T-lymphocyte (tee-LIM-fo-site), sometimes called a T-helper cell. CD4+ T-cells play a central role in the immune response. HIV enters CD4+ cells and uses the cell's machinery and energy to make new HIV particles. When HIV destroys CD4+ cells more rapidly than the body can replace them, the immune system becomes less effective at fighting cancers and infections caused by bacteria, viruses, parasites, and fungi, and AIDS develops. HIV can also attack some organs directly, including the brain, kidneys, and heart.

There are two major types of HIV. HIV-1 is the cause of the current epidemic. Different subtypes of HIV-1 occur in different parts of the world. HIV-2 is found in parts of West Africa and causes a milder form of AIDS.

HIV can mutate (change its genetic characteristics) with amazing speed, so that a single individual may be infected with different strains of the virus. Furthermore, HIV can quickly become resistant to antiretroviral medications (ARVs), rendering them ineffective. These are among the reasons that no vaccine or cure for HIV had been found as of the early 2000s.


It can take 5 to 15 years for HIV infection to develop into full-blown AIDS. During most of this period, people usually look and feel healthy. Unless they have been tested for HIV, they may not know that they are infected. However, if their condition is left untreated, most people with HIV eventually develop AIDS.

AIDS occurs when HIV has destroyed so many CD4+ cells that a person's T-cell count falls below a critical level, and the immune system can no longer fight off common infections. Many of these are opportunistic infections * (OIs) rarely occur in people with healthy immune systems, but can be life-threatening in AIDS patients. People with AIDS often repeatedly contract the same OI. AIDS patients are also more likely to develop certain cancers.

How Common Is HIV/AIDS?

Where Did HIV Come From?

Scientists suspected that HIV arose in Africa from a monkey virus known as SIV (simian immunodeficiency virus). The oldest known evidence of HIV was found in a blood sample taken from an African man who died in 1959. In 1999, an international team of researchers found a virus that appeared to be a genetic blend of HIV and SIV in a subspecies of chimpanzee, Pan troglodytes troglodytes. Researchers suspected that humans first became infected with SIV in the 1950s while hunting chimpanzees for food. Once in humans, the virus mutated into the deadlier HIV.


Viruses are tiny particles, much smaller than bacteria. They are made up mostly of genes * —either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid)—that code for a few proteins. Retroviruses such as HIV have RNA as their genetic material, which means that they reproduce themselves in a backward or “retro” manner.

When HIV enters the human bloodstream, it attaches to receptors on the surface of the CD4+ lymphocyte. It fuses with the cell membrane and injects its RNA into the cell. With the help of an HIV enzyme * called reverse transcriptase (RT), the HIV RNA is copied into DNA. Drugs called RT inhibitors prevent this copying of the viral RNA. The HIV enzyme called integrase inserts the HIV DNA in the host cell's genes, where it may remain hidden for some time.

When the CD4+ cell is activated by the immune system, cellular enzymes make RNA copies of the HIV DNA and long chains of HIV proteins. An HIV enzyme called a protease (PRO-tee-ace) cuts the large viral proteins into smaller pieces for making new HIV particles. Drugs known as protease inhibitors interfere with this cutting of the viral proteins.

New HIV particles are released from the lymphocyte and travel through the body, destroying other CD4+ cells. HIV reproduces itself very rapidly; several billion new viral particles may be produced every day. In addition, the HIV RT makes many mistakes, which results in the formation of different strains or variants of HIV in a single individual.

The United States

The Centers for Disease Control (CDC) estimated that 1,201,100 persons ages 13 years and older were living with HIV infection in 2012, including 168,300 people (14 percent) who were unaware of their infection. Between 2005 and 2015, the number of people living with HIV increased, while the annual number of new HIV infections remained relatively stable. However, about 50,000 new HIV cases were diagnosed each year.

In the United States, gay, bisexual, and other men who have sex with men (MSM), particularly young black/African American MSM, are most seriously affected by HIV. Young black MSM account for 45 percent of new HIV infections among black MSM and 55 percent of new HIV infections among young MSM overall. About 25 percent of new cases of HIV infection in the United States occur in young people between the ages of 13 and 24 years.


How Does HIV Spread?

Sexual intercourse, either homosexual (between men) or heterosexual (between men and women), is responsible for most HIV infections. Although there are documented cases of transmission of the virus as a result of sexual contact between two women, the incidence of transmission by this means is exceedingly small and close to zero. HIV can be transmitted through vaginal * , anal, or oral intercourse. The virus also spreads among people who share needles when they inject drugs. Infected mothers may pass HIV to their babies during pregnancy, childbirth, or breastfeeding. People can infect others with HIV before they have developed any symptoms or are aware that they are HIV-positive.

Having another sexually transmitted infection, such as syphilis * , genital herpes * , chlamydial * infection, gonorrhea * , or bacterial vaginosis * , appears to increase one's susceptibility to HIV infection during sex with an infected person.

HIV is spread through the mixing of body fluids, including the following:

HIV can be transmitted through any blood-to-blood contact. Because it can be difficult to see small breaks in the skin such as hangnails, precautions should be taken when coming into contact with any cut or wound on someone who could be infected with HIV. Medical personnel are at risk through accidental injuries with medical instruments—such as needles and scalpels—that have been contaminated with the blood of an HIV-infected patient. Although blood transfusions can spread HIV, blood donations and blood products in the United States have been screened for HIV since 1985, and the blood supply is considered to be safe.

* , or feces * .

Estimated Per-Act Probability of Acquiring HIV from an Infected Source, by Exposure Act*

Estimated Per-Act Probability of Acquiring HIV from an Infected Source, by Exposure Act*
SOURCE: Centers for Disease Control and Prevention, (accessed July 16, 2015). Table by Cenveo Publisher Services. © 2016 Cengage Learning ®.

What Are the Symptoms of HIV/AIDS?

HIV infection

Within two months after becoming infected with HIV, most people develop flulike symptoms, including a fever, sore throat, muscle aches, swollen glands or lymph nodes * , fatigue, and sometimes a measles-like rash. During this period, people are very infectious and the genital fluids contain large amounts of HIV. The illness usually disappears within a few weeks, and other symptoms may not appear for 5 to 15 years. Other people have no initial symptoms after contracting HIV. However, the virus can be transmitted to others even in the absence of symptoms.

Although some people have no symptoms of HIV infection until they develop AIDS, over the few years following HIV infection individuals may experience the following occasional symptoms:

Children, especially those infected before birth, generally develop symptoms more quickly than adults. Often these individuals are sick from birth or may fail to grow and develop at a normal rate.


The onset of AIDS is usually characterized by the appearance of OIs or cancers that commonly occur in people with severely weakened immune systems. Many of these conditions are considered to be AIDS-defining, meaning that they can constitute a diagnosis of AIDS. Although these illnesses may be treatable or preventable, they tend to recur repeatedly in AIDS patients. Most people who are said to have “died of AIDS” actually die from one of these illnesses.

The most common AIDS-related cancer is Kaposi's (kuh-POE-zees) sarcoma * (KS). KS is characterized by purplish nodules on the skin and is much more common among gay and bisexual men than among other HIV-infected groups. Other cancers associated with AIDS are non-Hodgkin lymphoma (the uncontrolled growth of lymphocytes), which can involve the central nervous system, liver, and bone marrow * . Lymphoma of the brain can occur in very late-stage AIDS. Invasive cervical cancer in women is also AIDS-associated.

AIDS dementia (dih-MEN-sha) complex is one of the few conditions that are directly caused by the effect of HIV on the brain. Dementia affects concentration, memory, and thinking.

How Is HIV/AIDS Diagnosed and Treated?

The HIV test

Doctors may suspect HIV infection from the symptoms, especially if a person has an OI. However, HIV infection can be diagnosed only by a blood test. The CDC recommends that individuals aged 13 to 64 years get tested at least once in their lifetime and that those with risk factors get tested more frequently. A general rule for those with risk factors is to get tested at least annually. Additionally, the CDC has reported that gay and bisexual men may benefit from getting an HIV test more often, perhaps every three to six months. Testing is recommended for all pregnant women and for newborns whose mothers are HIV-positive or were not tested during pregnancy. HIV testing is essential for anyone who may have been exposed to the virus or who has had multiple sexual partners or other risk factors.


Opportunistic infections (OIs) associated with AIDS can be caused by viruses, bacteria, parasites, or fungi, and they can affect every system in the body:

The most common test for HIV is a blood test to look for antibodies * Diagnosis of AIDS

The onset of AIDS in an HIV-positive individual is diagnosed by the appearance of one of about 26 AIDS-defining OIs or conditions. A blood test that measures the level of CD4+ lymphocytes in the body is performed periodically on HIV-infected people. AIDS is diagnosed if there are fewer than 200 CD4+ T-cells per cubic millimeter of blood, compared with 1,000 or more in healthy people.

Diagnosis in newborns

About one in four infants born to untreated HIV-infected mothers is HIV-positive. Sometimes infants who are not infected test positive for HIV antibodies for more than a year after birth, due to their mother's antibodies that passed through the placenta * . Therefore, additional tests are performed to determine whether an infant is in fact infected with HIV.

Diagnoses of HIV infection and AIDS in the United States, ages birth to 19 years, 2009–2013 Diagnoses in the United States of males and females aged birth to 19 years with HIV infection and AIDS,

Diagnoses of HIV infection and AIDS in the United States, ages birth to 19 years, 2009–2013 Diagnoses in the United States of males and females aged birth to 19 years with HIV infection and AIDS, 2009–2013, and number of deaths by age of persons diagnosed with HIV infection, 2009–2012.
SOURCE: Centers for Disease Control and Prevention. “HIV Surveillance Report.” Available at: (accessed December 9, 2015). Table by Lumina Datamatics Ltd. © 2016 Cengage Learning®.
Protease Inhibitors

Protease inhibitors have proven to be particularly effective in slowing the spread of HIV in the body. HIV uses its protease to cut the new long strands of viral protein into the smaller pieces needed to assemble new viral particles. Protease inhibitors interfere with the cutting action of the protease. Many of the new HIV copies are defective because they contain improperly cut pieces. These defective copies cannot infect other cells.

A combination of different types of drugs is prescribed in a treatment called HAART (highly active antiretroviral therapy). Drugs approved by the Food and Drug Administration (FDA) for treating HIV/AIDS include the following:

Regular blood tests measure the amount of HIV in the body (called the viral load) and the CD4+ cell count. If the viral load rises above its lowest point or the CD4+ count falls, the medications may be adjusted or changed. A given drug regimen or “AIDS cocktail” may fail for the following reasons:

HAART can reduce HIV to nearly undetectable levels in the bloodstream and enable the immune system to recover and fight off illness. However, the virus remains in the brain, lymph nodes, retina of the eye, and elsewhere in the body. HAART can also cause severe side effects and interactions with other medications.

If an HIV-infected woman is treated with particular ARVs during pregnancy and delivery, and the newborn is treated immediately after birth, the baby's risk of HIV infection drops from about 25 percent to about 6 percent. If mothers are treated with ARVs during pregnancy and deliver by cesarean section * , the risk of HIV infection in the newborn drops to about 1 percent. HIV-infected mothers are advised to feed their infants formula * to prevent transmitting the virus through their breast milk.

Complications of HIV/AIDS

In addition to AIDS-related OIs and cancers, HIV-infected people often have chronic hepatitis * B, caused by a virus. Viral hepatitis C infection, which can lead to severe liver damage and death, is very common among HIV-infected intravenous drug users. Complications of syphilis are also common with AIDS.

Various medications are used to treat or prevent OIs. For example, adults whose CD4+ cell counts drop below 200 and HIV-infected children whose T-cell counts are below normal are treated to prevent Pneumocystis pneumonia (PCP). Following an episode of PCP, the treatment is continued indefinitely. AIDS-associated cancers are treated with chemotherapy * , radiation, or alpha interferon.

Living with HIV/AIDS

As a result of HAART, individuals diagnosed with HIV can expect to live long lives. However, it is crucial that HIV-infected people do the following:

AIDS, and the infections that occur with the disorder, can affect many parts of the body.

AIDS, and the infections that occur with the disorder, can affect many parts of the body.
Illustration by Frank Forney. ©2016 Cengage Learning®.

How Can HIV/AIDS Be Prevented?

The best means of HIV/AIDS prevention is to avoid all contact with the bodily fluids of an infected person. Guidelines for preventing HIV infection include the following:

Individuals infected with HIV should inform their sexual partners of their status. Failure to do so can lead to prosecution in some countries. Sexual partners of those infected with HIV should be tested to determine if they are infected.

Some people with HIV infection seek others with HIV as sexual partners thinking they are not increasing the risk for the already infected partner or to themselves. However, there are different strains of HIV that can be transmitted to sexual partners. This infection with a new strain of HIV can result in the rapid decline in health status of an individual who was previously in stable health. In addition, this practice appears to be a major factor in the potential for increase in HIV drug resistance.

Avoiding sexual contact (abstinence), both homosexual and heterosexual, is the only sure way of preventing HIV infection by sexual transmission. The safest sexual relationship is between two uninfected people who have sex only with each other; however, people with HIV may seem completely healthy and often do not know they are infected. Practicing safer sex by always properly using a male latex condom or a female polyurethane condom for vaginal, anal, or oral sex reduces—but does not eliminate—the risk of HIV infection. Other forms of birth control such as spermicides, birth-control pills, or diaphragms offer no protection against the HIV virus.

Unfortunately, the availability and effectiveness of ARV drugs in the developed world have led to complacency among some people with regard to safe sex and other practices for preventing the spread of HIV. Meanwhile, intensive research in the United States and elsewhere continues to focus on finding an effective vaccine to protect against HIV and substances called microbicides to prevent transmission of the virus.

See also Cancer: Overview • Cervical Cancer • Chlamydial Infections • Chronic Illness • Cyclosporiasis and Cryptosporidiosis • Gay, Lesbian, Bisexual and Transgender Issues • Global Health Issues: Overview • Gonorrhea • Hepatitis • Immune Deficiencies • Immune System and Other Body Defenses: Overview • Lymphoma • Pneumonia • Pregnancy • Sarcoma • Sexually Transmitted Infections (STIs): Overview • Substance Abuse • Syphilis • Thrush • Viral Infections


Books and Articles

Gallant, Joel. 100 Questions & Answers about HIV and AIDS. Sudbury, MA: Jones and Bartlett, 2012.

Sax, Paul E., Calvin J. Cohen, and Daniel R. Kuritzkes. HIV Essentials. 7th ed. Sudbury, MA: Jones and Bartlett, 2014.

Stine, Gerald. AIDS Update 2014. New York: McGraw-Hill, 2013.


U.S. Department of Health and Human Services. “HIV/AIDS Basics.” (accessed March 11, 2016).

Organizations . U.S. Department of Health and Human Services, Room 443 H, 200 Independence Ave., Washington, DC 20201. Toll-free: 800-CDC-INFO (1-800-232-4636). Website: (accessed March 11, 2016).

amfAR, The Foundation for AIDS Research. 120 Wall St., 13th Floor, New York, NY 10005-3908. Toll-free: 800-39-amfAR. Website: (accessed March 11, 2016).

Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 800-232-4636. Website: (accessed March 11, 2016).

International AIDS Society. Avenue de France 23, CH-1202 Geneva 27, Switzerland. Telephone: 41 22 710 0800. Website: (accessed March 11, 2016).

UNAIDS. 20 Avenue Appia, CH-1211 Geneva 27, Switzerland. Telephone: 41 22 791 3666. Website: (accessed March 11, 2016).

* immune system (im-YOON SIS-tem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.

* opportunistic infections are infections caused by infectious agents that usually do not produce disease in people with healthy immune systems, but can cause widespread and severe illness in patients with weak or faulty immune systems.

* genes (JEENS) are chemical structures composed of deoxyribonucleic acid (DNA) that help determine a person's body structure and physical characteristics. Inherited from a person's parents, genes are contained in the chromosomes found in the body's cells.

* enzyme (EN-zime) is a protein that helps speed up a chemical reaction in cells or organisms.

* vaginal (VAH-jih-nul) refers to the canal in a woman that leads from the uterus to the outside of the body.

* syphilis (SIH-fih-lis) is a sexually transmitted infection that if untreated, can lead to serious lifelong problems throughout the body, including blindness and paralysis.

* chlamydial (kla-MIH-dee-ul) infection can occur in various forms in which the bacteria can invade the urinary and genital systems of the body as well as the eyes and lungs.

* genital herpes (GEN-eh-tal HERpees) is a viral infection transmitted by intimate contact with an infected person. The herpes simplex type 2 virus enters the mucous membranes and settles in nerves near the spinal column. When an infected person has an outbreak, the virus causes blisters at the infection site.

* gonorrhea (gah-nuh-REE-uh) is a sexually transmitted infection (STI) spread through all forms of sexual intercourse. Gonorrhea can affect the genitals, urethra, rectum, eyes, throat, joints, and other tissues of the body.

* bacterial vaginosis (back-TERi- all VAG-in-OH-sis) is a condition of the vagina caused by an overgrowth of normal bacteria. Symptoms include an abnormal discharge and fishy odor. This condition is treated with oral antibiotics and vaginal gels.

* semen (SEE-men) is the spermcontaining whitish fluid produced by the male reproductive tract.

* mucous membranes are the thin layers of tissue found inside the nose, ears, cervix (SER-viks) and uterus, stomach, colon and rectum, on the vocal cords, and in other parts of the body.

* urine is the liquid waste material secreted by the kidneys and removed from the body through the urinary tract.

* feces (FEE-seez) is the excreted waste from the gastrointestinal tract.

* lymph nodes (LIMF) are small bean-shaped masses of tissue containing immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

* sarcoma (sar-COHM-ah) is one of a group of tumors that occur in connective tissue and are mostly malignant.

* bone marrow is the soft tissue inside bones where blood cells are made.

* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.

* placenta (pluh-SEN-ta) is an organ that provides nutrients and oxygen to a developing baby; it is located within the womb during pregnancy.

* cesarean section (si-ZAR-ee-an SEK-shun) is the surgical incision of the walls of the abdomen and uterus to deliver offspring in cases where the mother cannot deliver through the vagina.

* formula is a prepared, nutritious drink or a dry drink mix designed specifically for infants.

* hepatitis (heh-puh-TIE-tis) is an inflammation of the liver. Hepatitis can be caused by viruses, bacteria, and a number of other noninfectious medical conditions.

* chemotherapy (KEE-mo-THER-apee) is the treatment of cancer with powerful drugs that kill cancer cells.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)