HIV/AIDS - HIV and AIDS

HIV/AIDS

The human immunodeficiency virus (HIV) weakens the body's immune defenses by destroying CD4 (T-cell) lymphocytes, which are a group of white blood cells that normally help guard the body against attacks by bacteria, viruses and other germs. When HIV destroys CD4 lymphocytes, the body becomes vulnerable to many different types of infections. These infections are called opportunistic because they have an opportunity to invade the body when the immune defenses are weak. HIV infection also increases the risk of certain cancers, illnesses of the brain (neurological) and nerves, body wasting and death. The entire spectrum of symptoms and illnesses that can happen when HIV infection significantly depletes the body's immune defenses is called acquired immunodeficiency syndrome or AIDS.

Since 1981, when HIV/AIDS was first recognized as a new illness, scientists have learned much about how a person becomes infected with HIV. The virus is spread through contact with an infected person's body fluids, especially through blood, semen and vaginal fluids. Once inside the body, HIV particles invade CD4 lymphocytes and use the cells' own genetic material to produce billions of new HIV particles. These new particles cause the infected CD4 cell to burst (lyse). The new particles can then enter the bloodstream and infect other cells. Once someone is infected with HIV, their number of normal CD4 cells continues to decrease.

Eventually, the number of normal CD4 cells drops below the threshold level needed to defend the body against infections, and the person develops AIDS. Doctors used to think that HIV was inactive (dormant or latent) between the initial infection and the diagnosis of AIDS. We now know that HIV is active, copying itself and killing CD4 cells from the time the infection starts through and beyond the diagnosis of AIDS.

Within the past two decades, about 60 million people worldwide have become infected with HIV. More than 20 million have died. More than 90% of these people live in developing countries. In some parts of Africa, more than half of adult deaths are caused by HIV infection, leaving millions of children orphaned after their parents died of AIDS. In the United States, as of the end of 2002, there were more than 886,000 cases of AIDS reported, with almost 500,000 deaths, including 5,315 children. HIV rates are increasing most rapidly among minority populations. The infection occurs 6 times as often in African-Americans and 3 times as often in Hispanics compared with whites.

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