HIV Infection and AIDS, An Overview, NIAID Fact Sheet
HIV Infection and AIDS: An Overview
Source: National Institute of Allergy and Infectious Diseases
AIDS — acquired immunodeficiency syndrome — was first reported in the United States in 1981 and has since become a major worldwide epidemic. AIDS is caused by the human immunodeficiency virus (HIV). By killing or damaging cells of the body’s immune system, HIV progressively destroys the body’s ability to fight infections and certain cancers. People diagnosed with AIDS may get life-threatening diseases called opportunistic infections, which are caused by microbes such as viruses or bacteria that usually do not make healthy people sick.
More than 700,000 cases of AIDS have been reported in the United States since 1981, and as many as 900,000 Americans may be infected with HIV. The epidemic is growing most rapidly among minority populations and is a leading killer of African American males. According to the U.S. Centers for Disease Control and Prevention (CDC), AIDS affects six times more African Americans than whites and three times more Hispanics than whites.
HIV is spread most commonly by having sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex.
HIV also is spread through contact with infected blood. Before blood was screened for evidence of HIV infection and before heat-treating techniques to destroy HIV in blood products were introduced, HIV was transmitted through transfusions of contaminated blood or blood components. Today, because of blood screening and heat treatment, the risk of getting HIV from such transfusions is extremely small.
HIV frequently is spread among injection drug users by the sharing of needles or syringes contaminated with very small quantities of blood from someone infected with the virus. It is rare, however, for a patient to give HIV to a health care worker or vice-versa by accidental sticks with contaminated needles or other medical instruments.
Women can transmit HIV to their babies during pregnancy or birth. Approximately one-quarter to one-third of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus. If the mother takes the drug AZT during pregnancy, she can reduce significantly the chances that her baby will be infected with HIV. If doctors treat mothers with AZT and deliver their babies by cesarean section, the chances of the baby being infected can be reduced to a rate of 1 percent.
A study sponsored by NIAID in Uganda found a highly effective and safe drug regimen for preventing transmission of HIV from an infected mother to her newborn that is more affordable and practical than any other examined to date. Interim results from the study show that a single oral dose of the antiretroviral drug nevirapine (NVP) given to an HIV-infected woman in labor and another to her baby within three days of birth reduces the transmission rate by half compared with a similar short course of AZT.
Although researchers have detected HIV in the saliva of infected individuals, no evidence exists that the virus is spread by contact with saliva. Laboratory studies reveal that saliva has natural properties that limit the power of HIV to infect. Research studies of people infected with HIV have found no evidence that the virus is spread to others through saliva such as by kissing. No one knows, however, whether so-called "deep kissing," involving the exchange of large amounts of saliva, or oral intercourse increase the risk of infection. Scientists also have found no evidence that HIV is spread through sweat, tears, urine, or feces.
Studies of families of HIV-infected people have shown clearly that HIV is not spread through casual contact such as the sharing of food utensils, towels and bedding, swimming pools, telephones, or toilet seats. HIV is not spread by biting insects such as mosquitoes or bedbugs.
HIV can infect anyone who practices risky behaviors such as: sharing drug needles or syringes, or having sexual contact with an infected person without using
a condom or with someone whose HIV status is unknown.
Having a sexually transmitted disease such as syphilis, genital herpes, chlamydial infection, gonorrhea, or bacterial vaginosis appears to make people more susceptible to acquiring HIV infection during sex with infected partners.
Many people do not develop any symptoms when they first become infected with HIV. Some people, however, have a flu-like illness within a month or two after exposure to the virus. This illness may include fever, headache, tiredness, and enlarged lymph nodes (organs of the immune system easily felt in the neck and groin). These symptoms usually disappear within a week to a month and are often mistaken for those of another viral infection. During this period, people are very infectious, and HIV is present in large quantities in genital fluids.
More persistent or severe symptoms may not surface for a decade or more after HIV first enters the body in adults, or within two years in children born with HIV infection. This period of "asymptomatic" infection is highly individual. Some people may begin to have symptoms as soon as a few months, while others may be symptom-free for more than 10 years. During the asymptomatic period, however, the virus is actively multiplying, infecting, and killing cells of the immune system. HIV’s effect is seen most obviously in a decline in the blood levels of CD4+ T cells (also called T4 cells) — the immune system’s key infection fighters. At the beginning of its life in the human body, the virus disables or destroys these cells without causing symptoms.
As the immune system deteriorates, a variety of complications start to take over. For many people, their first sign of infection is large lymph nodes or "swollen glands" that may be enlarged for more than three months. Other symptoms often experienced months to years before the onset of AIDS include: lack of energy, weight loss, frequent fevers and sweats, persistent or frequent yeast infections (oral or vaginal), persistent skin rashes or flaky skin, pelvic inflammatory disease in women that does not respond to treatment, or short-term memory loss.
Some people develop frequent and severe herpes infections that cause mouth, genital, or anal sores, or a painful nerve disease called shingles. Children may grow slowly or be sick a lot.
The term AIDS applies to the most advanced stages of HIV infection. The CDC in Atlanta, GA, develops official criteria for the definition of AIDS and is responsible for tracking the spread of AIDS in the United States.
CDC’s definition of AIDS includes all HIV-infected people who have fewer than 200 CD4+ T cells per cubic millimeter of blood. (Healthy adults usually have CD4+ T-cell counts of 1,000 or more.) In addition, the definition includes 26 clinical conditions that affect people with advanced HIV disease. Most of these conditions are opportunistic infections, which rarely cause harm in healthy people. In people with AIDS, these infections are often severe and sometimes fatal because the immune system is so ravaged by HIV that the body cannot fight off certain bacteria, viruses, fungi, parasites, and other microbes.
Opportunistic infections common in people with AIDS cause symptoms such as: coughing and shortness of breath, seizures and lack of coordination, difficult or painful swallowing, mental symptoms such as confusion and forgetfulnesss, severe and persistent diarrhea, fever, vision loss, nausea, abdominal cramps, and vomiting, weight loss and extreme fatigue, severe headaches, and coma.
Although children with AIDS may get the same opportunistic infections as adults with the disease, they also experience severe forms of the bacterial infections which all children may get, such as conjunctivitis (pink eye), ear infections, and tonsillitis.
People with AIDS are particularly prone to developing various cancers, especially those caused by viruses such as Kaposi’s sarcoma and cervical cancer, or cancers of the immune system known as lymphomas. These cancers are usually more aggressive and difficult to treat in people with AIDS. Signs of Kaposi’s sarcoma in light-skinned people are round brown, reddish, or purple spots that develop in the skin or in the mouth. In dark-skinned people, the spots are more pigmented.
During the course of HIV infection, most people experience a gradual decline in the number of CD4+ T cells, although some may have abrupt and dramatic drops in their CD4+ T-cell counts. A person with CD4+ T cells above 200 may experience some of the early symptoms of HIV disease. Others may have no symptoms even though their CD4+ T-cell count is below 200.
Many people are so debilitated by the symptoms of AIDS that they cannot hold steady employment or do household chores. Other people with AIDS may experience phases of intense life-threatening illness followed by phases in which they function normally.
A small number of people (fewer than 50) initially infected with HIV 10 or more years ago have not developed symptoms of AIDS. Scientists are trying to determine what factors may account for their lack of progression to AIDS, such as particular characteristics of their immune systems or whether they were infected with a less aggressive strain of the virus, or if their genes may protect them from the effects of HIV. Scientists hope that understanding the body’s natural method of control may lead to ideas for protective HIV vaccines and use of vaccines to prevent the disease from progressing.
Because early HIV infection often causes no symptoms, a doctor or other health care worker usually can diagnose it by testing a person’s blood for the presence of antibodies (disease-fighting proteins) to HIV. HIV antibodies generally do not reach levels in the blood which the doctor can see until one to three months following infection, and it may take the antibodies as long as six months to be produced in quantities large enough to show up in standard blood tests.
People exposed to the virus should get an HIV test as soon as they are likely to develop antibodies to the virus. By getting tested early, they can get the right treatment at a time when their immune systems are most able to combat HIV and thus prevent the emergence of certain opportunistic infections (seeTreatment below). Early testing also alerts HIV-infected people to avoid high-risk behaviors that could spread the virus to others.
Most doctors’ offices or health clinics can do HIV testing and will usually offer counseling to the patient at the same time. Of course, individuals can be tested anonymously at many sites if they are concerned about confidentiality.
Doctors diagnose HIV infection by using two different types of antibody tests, ELISA and Western Blot. If a person is highly likely to be infected with HIV and yet both tests are negative, a doctor may look for HIV itself in the blood. The person also may be told to repeat antibody testing at a later date, when antibodies to HIV are more likely to have developed.
Babies born to mothers infected with HIV may or may not be infected with the virus, but all carry their mothers’ antibodies to HIV for several months. If these babies lack symptoms, a definitive diagnosis of HIV infection using standard antibody tests cannot be made until after 15 months of age. By then, babies are unlikely to still carry their mothers’ antibodies and will have produced their own, if they are infected. New technologies to detect HIV itself are being used to more accurately determine HIV infection in infants between ages 3 months and 15 months. A number of blood tests are being evaluated to determine if they can diagnose HIV infection in babies younger than 3 months.
When AIDS first surfaced in the United States, no medicines were available to combat the underlying immune deficiency and few treatments existed for the opportunistic diseases that resulted. Over the past 10 years, however, researchers have developed drugs to fight both HIV infection and its associated infections and cancers.
The Food and Drug Administration has approved a number of drugs for treating HIV infection. The first group of drugs used to treat HIV infection, called nucleoside reverse transcriptase (RT) inhibitors, interrupts an early stage of the virus making copies of itself. Included in this class of drugs (called nucleoside analogs) are AZT (also known as zidovudine or ZDV), ddC (zalcitabine), ddI (dideoxyinosine), d4T (stavudine), and 3TC (lamivudine). These drugs may slow the spread of HIV in the body and delay the onset of opportunistic infections.
Non-nucleoside reverse transcriptase inhibitors (NNRTIs), such as delvaridine (Rescriptor) and nevirapine (Viramune), are also available for use in combination with other antiretroviral drugs.
More recently, a second class of drugs has been approved for treating HIV infection. These drugs, called protease inhibitors, interrupt virus replication at a later step in its life cycle. They include ritonavir (Norvir), saquinivir (Invirase), indinavir (Crixivan), amprenivir (Agenerase), and nelfinavir (Viracept). Because HIV can become resistant to both classes of drugs, combination treatment using both is necessary to effectively suppress the virus.
Currently available antiretroviral drugs do not cure people of HIV infection or AIDS, however, and they all have side effects that can be severe. Some of the nucleoside RT inhibitors may cause a depletion of red or white blood cells, especially when taken in the later stages of the disease. Some may also cause an inflammation of the pancreas and painful nerve damage. Other complications, including lactic acidosis and severe hepatomegaly (enlarged liver) with steatosis (fatty liver) that may result in liver failure and death, have also been reported with the use of antiretroviral nucleoside analogs alone or in combination, including AZT, ddI, ddC, 3TC, and abacavir.
The most common side effects associated with protease inhibitors include nausea, diarrhea, and other gastrointestinal symptoms. In addition, protease inhibitors can interact with other drugs resulting in serious side effects.
Researchers have credited highly active antiretroviral therapy, or HAART, as being a major factor in reducing the number of deaths from AIDS in this country by 47 percent in 1997. HAART is a combination of several drugs to treat patients. These drugs include reverse transcriptase inhibitors and protease inhibitors. Patients who are newly infected with HIV as well as AIDS patients can take the combination.
HAART is not a cure. The health of HIV and AIDS patients has benefited dramatically by combining protease inhibitors with other AIDS drugs, but there are drawbacks. Also, though HIV may not be found in the patients successfully treated with HAART, researchers know that it is still present, lurking in hiding places such as the lymph nodes, the brain, testes, and the retina of the eye.
A number of drugs are available to help treat opportunistic infections to which people with HIV are especially prone. These drugs include foscarnet and ganciclovir, used to treat cytomegalovirus eye infections, fluconazole to treat yeast and other fungal infections, and trimethoprim/sulfamethoxazole (TMP/SMX) or pentamidine to treat Pneumocystis carinii pneumonia (PCP).
In addition to antiretroviral therapy, adults with HIV whose CD4+ T-cell counts drop below 200 are given treatment to prevent the occurrence of PCP, which is one of the most common and deadly opportunistic infections associated with HIV. Children are given PCP preventive therapy when their CD4+ T-cell counts drop to levels considered below normal for their age group. Regardless of their CD4+ T-cell counts, HIV-infected children and adults who have survived an episode of PCP are given drugs for the rest of their lives to prevent a recurrence of the pneumonia.
HIV-infected individuals who develop Kaposi’s sarcoma or other cancers are treated with radiation, chemotherapy or injections of alpha interferon, a genetically engineered naturally occurring protein.
Because no vaccine for HIV is available, the only way to prevent infection by the virus is to avoid behaviors that put a person at risk of infection, such as sharing needles and having unprotected sex.
Many people infected with HIV have no symptoms. Therefore, there is no way of knowing with certainty whether a sexual partner is infected unless he or she has repeatedly tested negative for the virus — and has not engaged in any risky behavior.
People should either abstain from having sex or or use latex condoms, which may offer partial protection, during oral, anal, or vaginal sex. Only condoms made of latex should be used, and water-based lubricants should be used with latex condoms.
Although some laboratory evidence shows that spermicides can kill HIV, researchers have not found that these products can prevent a person from getting HIV.
The risk of HIV transmission from a pregnant woman to her baby is significantly reduced if she takes AZT during pregnancy, labor and delivery, and her baby takes it for the first six weeks of life.
NIAID-supported investigators are conducting an abundance of research on HIV infection, including the development and testing of HIV vaccines and new therapies for the disease and some of its associated conditions. Twenty-eight HIV vaccines are being tested in people, and many drugs for HIV infection or AIDS-associated opportunistic infections are either being developed or being tested. Researchers also are investigating exactly how HIV damages the immune system. This research is suggesting new and more effective targets for drugs and vaccines. NIAID-supported investigators also continue to trace how the disease progresses in different people.
Scientists are investigating and testing chemical barriers, such as topical microbicides, that people can use in the vagina or in the rectum during sex to prevent HIV transmission. They also are looking at other ways to prevent transmission such as controlling sexually transmitted diseases and modifying people’s behavior as well as ways to prevent transmission from mother to child.
For information about Food and Drug Administration-approved HIV-related clinical trials being conducted throughout the United States, call the AIDS Clinical Trials Information Service:
1-800-243-7012 (TDD/Deaf Access)
For federally approved treatment guidelines on HIV/AIDS, call the HIV/AIDS Treatment Information Service:
1-800-243-7012 (TDD/Deaf Access)
Both services operate from 9 a.m. to 7 p.m. Eastern Time, Monday through Friday. Spanish-speaking specialists are available.
To obtain information specifically about clinical trials conducted by the NIAID Intramural AIDS Research Program, call 1-800-243-7644.
To obtain materials for adolescents with HIV, or more information about adolescents and HIV, contact the National Prevention Information Network at 1-800-458-5231 or 1-800-243-7012 (TDD/Deaf Access).
NIAID, a component of the National Institutes of Health, supports research on AIDS, tuberculosis and other infectious diseases as well as allergies and immunology.
Office of Communications and Public Liaison
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892
Public Health Service
U.S. Department of Health and Human Services