Acquired Immune Deficiency Syndrome, or AIDS, is the result of infection by HIV. The virus destroys the patient's immune system, leaving them susceptible to any infection or other diseases that they contract.
AIDS was first noticed by doctors treating gay men in New York City in the early 1980s. They were developing very rare cancers, such as non-Hodgkin's Lymphoma, and testing found that their immune systems were being destroyed. However, it was not until the early 1990s that an American team managed to isolate the virus that was responsible - HIV. HIV only infected T cells, a vital part of the body's immune system. Moreover, HIV could go through long periods of dormancy and was rarely found in the blood or other tissues of the body. Further research indicated that at least one patient in Great Britain in the 1950s who had died of tuberculosis, was also HIV-positive, and it is likely that deaths from the disease were common and were mistaken for death from other common infections of the time.
Life expectancy for HIV positive patients in North America and Europe has been extended greatly, thanks to the development of AZT and other anti-viral medications that attack the virus while it seeks new cells to infect. However, it has to date resisted all attempts at vaccination. While treatment and proper care can extend the life of HIV positive patients, such patients inevitably fall victim to AIDS.
AIDS patients are also very susceptible to infection. Even minor infections can turn out to be fatal.