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HIV/AIDS Science

January 22, 2007

What is HIV?

HIV (human immunodeficiency virus) is the virus that causes AIDS. This virus may be passed from one person to another when infected blood, semen, or vaginal secretions come in contact with an uninfected person's broken skin or mucous membranes.* In addition, infected pregnant women can pass HIV to their baby during pregnancy or delivery, as well as through breast-feeding. People with HIV have what is called HIV infection. Some of these people will develop AIDS as a result of their HIV infection.

For more information see "What is AIDS?"

* A mucous membrane is wet, thin tissue found in certain openings to the human body. These can include the mouth, eyes, nose, vagina, rectum, and opening of the penis.

Where did HIV come from?

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The earliest known case of HIV-1 in a human was from a blood sample collected in 1959 from a man in Kinshasa, Democratic Republic of Congo. (How he became infected is not known.) Genetic analysis of this blood sample suggested that HIV-1 may have stemmed from a single virus in the late 1940s or early 1950s.

We know that the virus has existed in the United States since at least the mid- to late 1970s. From 1979-1981 rare types of pneumonia, cancer, and other illnesses were being reported by doctors in Los Angeles and New York among a number of male patients who had sex with other men. These were conditions not usually found in people with healthy immune systems.

In 1982 public health officials began to use the term "acquired immunodeficiency syndrome," or AIDS, to describe the occurrences of opportunistic infections, Kaposi's sarcoma (a kind of cancer), and Pneumocystis carinii pneumonia in previously healthy people. Formal tracking (surveillance) of AIDS cases began that year in the United States.

In 1983, scientists discovered the virus that causes AIDS. The virus was at first named HTLV-III/LAV (human T-cell lymphotropic virus-type III/lymphadenopathy-associated virus) by an international scientific committee. This name was later changed to HIV (human immunodeficiency virus).

For many years scientists theorized as to the origins of HIV and how it appeared in the human population, most believing that HIV originated in other primates. Then in 1999, an international team of researchers reported that they had discovered the origins of HIV-1, the predominant strain of HIV in the developed world. A subspecies of chimpanzees native to west equatorial Africa had been identified as the original source of the virus. The researchers believe that HIV-1 was introduced into the human population when hunters became exposed to infected blood.

For more information on this discovery, visit the NIH National Institute of Allergy and Infectious Diseases press release at www.niaid.nih.gov/newsroom/releases/hivorigin.htm.

What is AIDS?

AIDS stands for Acquired Immunodeficiency Syndrome.

Acquired -- means that the disease is not hereditary but develops after birth from contact with a disease causing agent (in this case, HIV).

Immunodeficiency -- means that the disease is characterized by a weakening of the immune system.

Syndrome -- refers to a group of symptoms that collectively indicate or characterize a disease. In the case of AIDS this can include the development of certain infections and/or cancers, as well as a decrease in the number of certain cells in a person's immune system.

A diagnosis of AIDS is made by a physician using specific clinical or laboratory standards.

For more information see "What Causes AIDS?" and "What is HIV?"

What causes AIDS?

AIDS is caused by infection with a virus called human immunodeficiency virus (HIV). This virus is passed from one person to another through blood-to-blood and sexual contact. In addition, infected pregnant women can pass HIV to their babies during pregnancy or delivery, as well as through breast feeding. People with HIV have what is called HIV infection. Some of these people will develop AIDS as a result of their HIV infection.

For more information see "What is HIV?"

How does HIV cause AIDS?

HIV destroys a certain kind of blood cell (CD4+ T cells) which is crucial to the normal function of the human immune system. In fact, loss of these cells in people with HIV is an extremely powerful predictor of the development of AIDS. Studies of thousands of people have revealed that most people infected with HIV carry the virus for years before enough damage is done to the immune system for AIDS to develop. However, sensitive tests have shown a strong connection between the amount of HIV in the blood and the decline in CD4+ T cells and the development of AIDS. Reducing the amount of virus in the body with anti-retroviral therapies can dramatically slow the destruction of a person's immune system.

For more information:

How long does it take for HIV to cause AIDS?

Prior to 1996, scientists estimated that about half the people with HIV would develop AIDS within 10 years after becoming infected. This time varied greatly from person to person and depended on many factors, including a person's health status and their health-related behaviors.

Since 1996, the introduction of powerful anti-retroviral therapies has dramatically changed the progression time between HIV infection and the development of AIDS. There are also other medical treatments that can prevent or cure some of the illnesses associated with AIDS, though the treatments do not cure AIDS itself. Because of these advances in drug therapies and other medical treatments, estimates of how many people will develop AIDS and how soon are being recalculated, revised, or are currently under study.

As with other diseases, early detection of infection allows for more options for treatment and preventative health care.

Why do some people make statements that HIV does not cause AIDS?

The epidemic of HIV and AIDS has attracted much attention both within and outside the medical and scientific communities. Much of this attention comes from the many social issues related to this disease such as sexuality, drug use, and poverty. Although the scientific evidence is overwhelming and compelling that HIV is the cause of AIDS, the disease process is still not completely understood. This incomplete understanding has led some persons to make statements that AIDS is not caused by an infectious agent or is caused by a virus that is not HIV. This is not only misleading, but may have dangerous consequences. Before the discovery of HIV, evidence from epidemiologic studies involving tracing of patients' sex partners and cases occurring in persons receiving transfusions of blood or blood clotting products had clearly indicated that the underlying cause of the condition was an infectious agent. Infection with HIV has been the sole common factor shared by AIDS cases throughout the world among men who have sex with men, transfusion recipients, persons with hemophilia, sex partners of infected persons, children born to infected women, and occupationally exposed health care workers.

The conclusion after more than 20 years of scientific research is that people, if exposed to HIV through sexual contact or injecting drug use for example, may become infected with HIV. If they become infected, most will eventually develop AIDS.

For more information, visit the NIH National Institute for Allergies and Infectious Diseases Fact sheet "The Evidence That HIV Causes AIDS."

How well does HIV survive outside the body?

Scientists and medical authorities agree that HIV does not survive well outside the body, making the possibility of environmental transmission remote. HIV is found in varying concentrations or amounts in blood, semen, vaginal fluid, breast milk, saliva, and tears. To obtain data on the survival of HIV, laboratory studies have required the use of artificially high concentrations of laboratory-grown virus. Although these unnatural concentrations of HIV can be kept alive for days or even weeks under precisely controlled and limited laboratory conditions, CDC studies have shown that drying of even these high concentrations of HIV reduces the amount of infectious virus by 90 to 99 percent within several hours. Since the HIV concentrations used in laboratory studies are much higher than those actually found in blood or other specimens, drying of HIV-infected human blood or other body fluids reduces the theoretical risk of environmental transmission to that which has been observed -- essentially zero. Incorrect interpretations of conclusions drawn from laboratory studies have in some instances caused unnecessary alarm.

Results from laboratory studies should not be used to assess specific personal risk of infection because (1) the amount of virus studied is not found in human specimens or elsewhere in nature, and (2) no one has been identified as infected with HIV due to contact with an environmental surface. Additionally, HIV is unable to reproduce outside its living host (unlike many bacteria or fungi, which may do so under suitable conditions), except under laboratory conditions; therefore, it does not spread or maintain infectiousness outside its host.

How can I tell if I'm infected with HIV?

The only way to know if you are infected is to be tested for HIV infection. You cannot rely on symptoms to know whether or not you are infected. Many people who are infected with HIV do not have any symptoms at all for 10 years or more.

The following may be warning signs of advanced HIV infection:

  • rapid weight loss
  • dry cough
  • recurring fever or profuse night sweats
  • profound and unexplained fatigue
  • swollen lymph glands in the armpits, groin, or neck
  • diarrhea that lasts for more than a week
  • white spots or unusual blemishes on the tongue, in the mouth, or in the throat
  • pneumonia
  • red, brown, pink, or purplish blotches on or under the skin or inside the mouth, nose, or eyelids
  • memory loss, depression, and other neurological disorders

However, no one should assume they are infected if they have any of these symptoms. Each of these symptoms can be related to other illnesses. Again, the only way to determine whether you are infected is to be tested for HIV infection. For information on where to find an HIV testing site, visit the National HIV Testing Resources Web site at www.hivtest.org or call CDC-INFO 24 Hours/Day at1-800-CDC-INFO (232-4636), 1-888-232-6348 (TTY), in English, en Español. These resources are confidential. You can also ask your health care provider to give you an HIV test.

You also cannot rely on symptoms to establish that a person has AIDS. The symptoms of AIDS are similar to the symptoms of many other illnesses. AIDS is a medical diagnosis made by a doctor based on specific criteria established by the CDC. For more information refer to the Morbidity and Mortality Weekly Report "1993 Revised Classification System for HIV Infection and Expanded Surveillance Case Definition for AIDS Among Adolescents and Adults" at www.cdc.gov/mmwr/preview/mmwrhtml/00018871.htm.

If you would like more information or have personal concerns, call CDC-INFO 24 Hours/Day at 1-800-CDC-INFO (232-4636), 1-888-232-6348 (TTY), in English, en Español.



  
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This article was provided by U.S. Centers for Disease Control and Prevention. Visit the CDC's website to find out more about their activities, publications and services.
 
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