AIDS (acquired immunodeficiency syndrome) is one of the worst pandemics the world has ever known. HIV (human immunodeficiency virus) is the virus that causes AIDS. First discovered in 1981 in a remote area of central Africa, it has since swept across the globe, infecting millions in a relatively short period of time.

HIV can be transmitted by:

  • Sexual contact
  • Contaminated intravenous needles
  • Breastfeeding (mother to baby)
  • Mother to fetus during pregnancy or birth
  • Blood transfusions (rare in countries where blood is screened for HIV antibodies)

Like all viruses, HIV treads the fine line that separates living things from nonliving things. Viruses lack the chemical machinery that human cells utilize to support life. So, HIV requires a host cell to stay alive and replicate. To replicate, the virus creates new virus particles inside a host cell, and those particles carry the virus to new cells.

HIV infects one particular type of immune-system cell. This cell is called the CD4+ T-cell, also know as the T-helper cell (see How Your Immune System Works for details on T-cells). Once the HIV virus enters the body, it heads for the lymphoid tissues, where it finds the T-helper cells. The T-helper cell turns into an HIV-replicating cell once it is infected. In a healthy person, there are typically 1 million T-cells per 1 milliliter of blood.

The newly replicated virus particles infect other T-helper cells, causing the person's T-helper cell count to slowly dwindle. T-helper cells play a vital role in the body's immune response, so the lack of T-helper cells compromises the immune system. When a person's T-helper cell count drops below 200,000 cells per 1 milliliter of blood, he or she is considered to have AIDS. The development of AIDS takes about two to 15 years, but about half of all people with HIV will develop AIDS within 10 years after becoming infected, according to the Centers for Disease Control (CDC).

HIV cannot be transmitted by:

  • Saliva, tears and sweat - Saliva and tears contain only small amounts of HIV; scientists haven't detected any HIV in the sweat of an infected person.
  • Insects - Studies show no evidence of HIV transmission through bloodsucking insects, even in areas where there are many cases of AIDS and large populations of mosquitoes.
  • Using the same toilet seat
  • Swimming in the same pool
  • Touching, hugging or shaking hands
  • Eating in the same restaurant
  • Sitting next to someone

No one dies from AIDS or HIV specifically. An AIDS-infected person dies from infections, because his or her immune system is so weakened. An AIDS patient could die from the common cold as easily as from cancer. The person's body cannot fight off the infection, and he or she eventually dies from something that a non-HIV-infected person could have quickly recovered from.

See the next page for more information.