Human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS), which is deadly if left untreated. An HIV infection damages the immune system, your body's defense against disease and infection. A person can die from "opportunistic" infections from bacteria, viruses and other types of microscopic organisms that are usually harmless to healthy people. Because the immune system is damaged, the body of someone with this condition cannot defend itself well. AIDS is the final stage of HIV infection, when opportunistic infections occur because of a greatly weakened immune system.

The white blood cells (lymphocytes) in our bodies work to protect us against infection. Lymphocytes include B cells and T cells. B cells produce antibodies that destroy organisms invading the body. T cells help regulate the production of these antibodies.

Some T cells are helper cells; others are suppressor cells. T helper cells help create antibodies and so-called cell-mediated immunity that also assist in the defense against certain infections. Suppressor cells end the immune reaction. The HIV virus targets a specific kind of T helper cell called CD4 cells. HIV attacks CD4 cells and uses them to make more copies of the HIV virus. As CD4 cells are destroyed, the immune system fails and AIDS develops.

In the United States, more than half a million people have died from AIDS, and about 40,000 people are infected annually. As of 2005, an estimated 438,000 Americans were living with AIDS.

Prognosis

Since 1996, the introduction of powerful antiretroviral therapies has dramatically decreased the number of people who develop AIDS. Before better therapies and medical treatments existed to take care of complications, it was thought people could live an average of 10 years after HIV infection.

Early detection of HIV infection can extend your life if you are treated with antiretroviral therapy, but to date, this infection cannot be cured. These medications must be taken for life.