Like HowStuffWorks on Facebook!


HIV/AIDS is an infectious disease. The letters stand for Human Immunodeficiency Virus, which is the name of the organism that causes this disease, and Acquired Immune Deficiency Syndrome, which is the name of the set of symptoms that characterize this condition.

AIDS was first recognized as a new disease in 1981, when a number of young gay men in New York and Los Angeles were diagnosed with symptoms not usually seen in individuals with healthy immune systems. This information was reported to the Centers for Disease Control and Prevention (CDC), the branch of the U.S. government that monitors and tries to control disease outbreaks.

Many new cases were soon discovered of what appeared to be a disease associated with the breakdown of the body's immune or natural defense system.

Normally, the immune system, which consists of a wide array of cells that can identify and eliminate invading bacteria, fungus, viruses and other disease-causing pathogens, is able to protect us from harm. One part of the immune response involves the creation of antibodies, which are chemical substances that fight against infectious agents.

HIV/AIDS — "Opportunistic" Infections

If there is damage to our immune system, however, antibodies and other bodily defenses may not be produced and we are subject to many different infectious diseases, including those called "opportunistic infections" that are usually only able to strike when the body's defenses are weakened.

Although the first cases of the disease that came to be called AIDS were among homosexual men, within a few months the same strange set of symptoms was being seen in female patients and hemophiliacs, and before long injection drug users and their non-drug using sex partners and children also were being diagnosed with AIDS. It became clear to the CDC that we were facing a significant new epidemic.