AIDS stands for Acquired Immunodeficiency (or Immune Deficiency) Syndrome. It results from infection with a virus called HIV, which stands for Human Immunodeficiency Virus. This virus infects key cells in the human body called CD4-positive (CD4+) T cells. These cells are part of the body's immune system, which fights infections and various cancers.

When HIV invades the body's CD4+ T cells, the damaged immune system loses its ability to defend against diseases caused by bacteria, viruses, and other microscopic organisms. A substantial decline in CD4+ T cells also leaves the body vulnerable to certain cancers.

There is no cure for AIDS, but medical treatments can slow down the rate at which HIV weakens the immune system. As with other diseases, early detection offers more options for treatment and preventing complications.

What Is The Difference Between HIV And AIDS?

The term AIDS refers to an advanced stage of HIV infection, when the immune system has sustained substantial damage. Not everyone who has HIV infection develops AIDS.

When HIV progresses to AIDS, however, it has proved to be a universally fatal illness. Few people survive five years from the time they are diagnosed with AIDS, although this is increasing with improvements in treatment techniques.

Experts estimate that about half the people with HIV will develop AIDS within 10 years after becoming infected. This time varies greatly from person to person, however, and can depend on many factors, including a person's health status and health-related behaviors.

People are said to have AIDS when they have certain signs or symptoms specified in guidelines formulated by the U.S. Centers for Disease Control and Prevention (CDC).

The CDC's definition of AIDS includes:

• All HIV-infected people with fewer than 200 CD4+ T cells per cubic millimeter of blood (compared with CD4+ T cell counts of about 1,000 for healthy people)
• People with HIV infection who have at least one of more than two dozen AIDS-associated conditions that are the result of HIV's attack on the immune system

AIDS-associated conditions include:

• Opportunistic infections by bacteria, fungi, and viruses. Opportunistic infections are infections that are rarely seen in healthy people but occur when a person's immune system is weakened.
• The development of certain cancers (including cervical cancer and lymphomas).
• Certain autoimmune disorders.

Most AIDS-associated conditions are rarely serious in healthy individuals. In people with AIDS, however, these infections are often severe and sometimes fatal because the immune system is so damaged by HIV that the body cannot fight them off.

The History Of AIDS

The symptoms of AIDS were first recognized in the early 1980s:

• In 1981, a rare lung infection called Pneumosystis carinii pneumonia began to appear in homosexual men living in Los Angeles and New York.
• At the same time, cases of a rare tumor called Kaposi's sarcoma were also reported in young homosexual men. These tumors had been previously known to affect elderly men, particularly in parts of Africa. New appearances of the tumors were more aggressive in the young men and appeared on parts of the body other than the skin.
• Other infections associated with weakened immune defenses were also reported in the early 1980s.

Groups most frequently reporting these infections in the early 1980s were homosexuals, intravenous drug users, and people with hemophilia, a blood disorder that requires frequent transfusions. Blood and sexual transmission were therefore suspected as the sources for the spread of the infections.

In 1984, the responsible virus was identified and given a name. In 1986, it was renamed the human immunodeficiency virus (HIV).