Acquired Immunodeficiency Syndrome (AIDS)

What does AIDS stand for? What causes AIDS?

AIDS stands for "acquired immunodeficiency syndrome." AIDS is a disease that weakens the immune system to the point where an affected person is vulnerable to a wide range of infections and cancers that result in death if not treated. AIDS is caused by the human immunodeficiency virus (HIV). The virus is spread through contact with infected blood or secretions. At first (stage 1 HIV infection), there is little evidence of harm. Over time, the virus attacks the immune system, focusing on special cells called "CD4 cells" which are important in protecting the body from infections and cancers, and the number of these cells starts to fall (stage 2). Eventually, the CD4 cells fall to a critical level and/or the immune system is weakened so much that it can no longer fight off certain types of infections and cancers. This advanced stage of infection (stage 3) with HIV is called AIDS.
HIV is a very small virus that contains ribonucleic acid (RNA) as its genetic material. (Animal cells, plant cells, bacteria, parasites, and some viruses use deoxyribonucleic acid [DNA] as their primary genetic material rather than RNA.) When HIV infects animal cells, it uses a special enzyme, reverse transcriptase, to turn (transcribe) its RNA into DNA which, in turn, directs the formation of HIV RNA that can be used to form new HIV. This is different from the way human cells reproduce (directly transcribing their DNA into RNA), so HIV is classified as a "retrovirus." When HIV reproduces, it is prone to making small genetic mistakes or mutations, resulting in viruses that vary slightly from each other. This ability to create minor variations allows HIV to evade the body's immunologic defenses, essentially leading to lifelong infection, and has made it difficult to make an effective vaccine. The mutations also allow HIV to become resistant to medications.

What is the history of AIDS?

Careful investigation has helped scientists determine where AIDS came from. Studies have shown that the human immunodeficiency virus first arose in Africa. It spread from primates to people decades ago, possibly when humans came into contact with infected blood during a chimpanzee hunt. By testing stored blood samples, scientists have found evidence of human infection as long ago as 1959. Once introduced into humans, HIV was spread through sexual intercourse from person to person. As infected people moved around, the virus spread from Africa to other areas of the world. In 1981, U.S. physicians noticed that a large number of young men were dying of unusual infections and cancers. Initially, U.S. victims were predominately homosexual men, probably because the virus inadvertently entered this population first in this country and because the virus is transmitted easily during anal intercourse. However, it is important to note that the virus also is efficiently transmitted through heterosexual activity and contact with infected blood or secretions. In Africa, which remains the center of the AIDS pandemic, most cases are heterosexually transmitted.
In the years since the virus was first identified, AIDS has spread to every corner of the globe. Statistics from the World Health Organization show that approximately 2 million people die each year from AIDS, resulting in 15 million new orphan children. Worldwide, half of HIV-infected people are women and 6% are children under 15 years of age. Two-thirds of current cases are in sub-Saharan Africa.
In the U.S., more than 1 million people have been diagnosed with AIDS since the start of the epidemic. There are approximately 430,000 people currently living with AIDS in the U.S. Each year, another 37,000 people are newly diagnosed with AIDS. Over the years, more than half a million people in the U.S. have died from AIDS, many of them during what should have been their most productive years of life.