Acquired Immune Deficiency Syndrome (AIDS) is a condition characterized by damage to the human immune system, which allows infections that would otherwise be controlled to run riot. These infections, which are called opportunistic infections, would be relatively minor to someone with a strong immune system, but can lead to death for those with AIDS.
This condition is caused by a virus, the Human Immunodeficiency Virus (HIV). The length of time between infection with HIV and the development of AIDS can be lengthened by drug regimens, but even without treatment there is still usually a lag time of several years. This means that those unknowingly infected with HIV have a number of years during which they might accidentally infect others.
HIV is transmitted through bodily fluids, notably semen, blood and breast milk. Tears, saliva and sweat may contain the virus, but in such low concentrations that transmission via these fluids is virtually impossible. People are most commonly infected through unprotected sexual intercourse or the sharing of unsterilized needles among intravenous drug-users.
When AIDS was first identified, it was found to cluster in the gay population in California, and for a number of years it was unfairly stigmatized as a "gay disease." This led to some heterosexuals and children with the condition being discriminated against, with some children being forced from their schools.
The disease is thought to have originated in Sub-Saharan Africa. In Africa, unlike the US, the main route of transmission is heterosexual sex, and AIDS has had enormously destructive impact on a number of African countries, cutting a swath through the most productive demographic — young, sexually-active adults. An unwillingness to speak frankly about what causes the condition slowed international reaction to this disease, but some nations are now successfully slowing the spread of AIDS through widespread advocacy of the use of condoms.
In the US, its spread has been slowed by education in safe sex methods and the development of treatments for the HIV-infected that delay the onset of full-blown AIDS. Whereas in the early days, a person diagnosed with HIV had only a few years to live, though the disease is still fatal — one doesn't 'recover' from it — people generally have a longer life expectancy and a longer lag time before progressing from HIV. The concept of living with AIDS is one the world is just starting to get used to, although the drug therapies are expensive and unavailable in poorer countries.