AIDS is caused by the human immunodeficiency virus (HIV). By killing or damaging cells of the body's immune system, this virus progressively destroys the body's ability to fight infections and certain cancers. HIV is typically spread through unprotected sex with an infected partner or through contact with contaminated blood, such as by sharing needles or syringes.
When first infected with the virus, many people do not have symptoms, although some will have a flu-like illness within a month or two. HIV is typically treated with medications, specifically antiretroviral drugs. Although they do not cure people of the virus, or of AIDS, these drugs can help slow the spread of the virus in the body and delay the start of opportunistic infections.
(For more info on this topic, click HIV. This article takes a closer look at how it is transmitted and gives an overview of how a diagnosis is made.)