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Frequently Asked Questions About HIV/AIDS (Part One)

January 2010

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What exactly is AIDS?

AIDS is a disease caused by a virus called HIV (human immunodeficiency virus). AIDS stands for Acquired Immunodeficiency Syndrome.

In this disease, HIV damages the immune system, so the body is no longer able to fight off diseases that normally it would be able to fight off.

HIV infects and eventually destroys a specific type of cell in your immune system called a CD4 cell (also called a T4 cell or a T helper cell).

Think of the CD4 cells as the generals of the immune-system army. The CD4 cells tell other immune-system cells what to do when an invading organism, germ or cancer cell is found in the body. Basically HIV kills off the CD4 cells (that is, it kills off the generals of the army). When the generals of the immune-system army are killed off, the rest of the immune system doesn't know what to do to fight off invaders. This is how HIV damages the immune system.

When HIV first enters the body, your immune system immediately attacks the virus, and keeps it under control for a number of years. During this time, the virus is at constant battle with your immune system. Your body tries to get rid of the virus, but is only able to keep it under control.

After a number of years, your immune system starts to lose its battle against HIV. Then, after an average of 10 years of fighting HIV, if you're not taking HIV treatment, your immune system starts to weaken. This is when full-blown AIDS begins. During this 10-year period, a person may have no symptoms at all, and feel fine and look fine. During this time, the person is considered HIV positive, but does not yet have AIDS.

Definition of AIDS

The definition of AIDS in the U.S. is a very specific one. In order to be diagnosed with AIDS, a person must meet the following requirements:

First, a person must be diagnosed with either HIV-1 or HIV-2.

Second, in addition to having HIV, a person must have at least one of the following:

  1. A CD4 cell count of less than 200.
  2. A CD4 cell count percentage of less than 14%.
  3. An opportunistic disease as defined by the U.S. Centers for Disease Control and Prevention (CDC). (For a list of opportunistic infections, click here.)

The normal CD4 cell count ranges between 800 and 1,200, or greater than 29%. A cell count below 500 or below 29% indicates an initially damaged immune system. A cell count below 200 or below 14% indicates a severely damaged immune system. An opportunistic disease is a disease that primarily causes illness given the opportunity of a damaged immune system.

If a person has HIV and meets any of the three criteria above, he or she is considered to have full-blown AIDS. If a person doesn't have HIV, or doesn't meet one of the three additional requirements above, they do not meet the definition of AIDS.

Note that if a person with HIV has a severely damaged immune system (that is, a CD4 count less than 200 or less than 14%), he or she meets the definition of AIDS even if they do not have an opportunistic disease. It is therefore possible for a person to have full-blown AIDS and have no symptoms at all. If a person has HIV and an opportunistic disease, they also meet the definition of full-blown AIDS. When a person does show symptoms, it is usually due to one of the opportunistic diseases.

Also, once someone has been diagnosed with AIDS, they will always be considered to have AIDS, regardless of any clinical changes later on. For example, if a person has HIV, and a CD4 cell count below 200, they are considered to have AIDS. If their CD4 cell count later goes back above 200, they are still considered to have AIDS.

Which body fluids can transmit the HIV virus, and which ones don't?

Blood, pre-cum, semen, vaginal secretions and breast milk all contain high concentrations of HIV, and all have been linked to transmission of the virus.

Saliva, tears, sweat and urine can have the virus in them, but in such small concentrations that nobody has ever been infected through them. However, if any body fluid is visibly contaminated with blood, the risk of transmission exists.

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This article was provided by Rick Sowadsky, M.S.P.H..
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