Acquired immune deficiency syndrome, or AIDS, is a recently recognized disease. It is caused by infection with the human immunodeficiency virus (HIV), which attacks selected cells in the IMMUNE SYSTEM and produces defects in function. These defects may not be apparent for years. They lead, however, to a severe suppression of the immune system's ability to resist harmful organisms. This leaves the body open to invasion by various infections, which are therefore called opportunistic diseases, and to the development of unusual cancers. The virus also tends to reach certain brain cells. This leads to so-called neuropsychiatric abnormalities, or psychological disturbances caused by physical damage to nerve cells. Since the first AIDS cases were reported in 1981, through mid-1994 more than 402,000 AIDS cases and more than 241,000 deaths have been reported in the United States alone. This is only the tip of the iceberg of HIV infection, however. It is estimated that nearly 1 million Americans had been infected with the virus through the mid-1990s but had not yet developed clinical symptoms. In addition, although the vast majority of documented cases have occurred in the United States, AIDS cases have also been reported in almost every country in the world. Sub-Saharan Africa in particular appears to suffer a heavy burden of this illness. No cure or vaccine now exists for AIDS. Many of those infected with HIV may not even be aware that they carry and can spread the virus. Combating it is a major challenge to biomedical scientists and health-care providers. HIV infection and AIDS represent among the most pressing public-policy and public-health problems worldwide. Definition of AIDS The U.S. CENTERS FOR DISEASE CONTROL AND PREVENTION has established criteria for defining cases of AIDS that are based on laboratory evidence such as T4 cell count, the presence of certain opportunistic diseases, and a range of other conditions. The opportunistic diseases are generally the most prominent and life-threatening clinical manifestations of AIDS. It is now recognized, however, that neuropsychiatric manifestations of HIV infection of the brain are also common. Other complications of HIV infection include fever, diarrhea, severe weight loss, and swollen lymph nodes. When HIV-infected persons experience some of the above symptoms but do not meet full criteria for AIDS, they are given the diagnosis of AIDS-related complex, or ARC. The growing feeling is that ARC and HIV infection without symptoms should not be viewed as distinct entities but, rather, as stages of an irreversible progression toward AIDS. Historical Background In the late 1970s, certain rare cancers and a variety of serious infections were recognized to be occurring in increasing numbers of previously healthy persons. Strikingly, these were disorders that would hardly ever threaten persons with normally functioning immune systems. First formally described in 1981, AIDS was observed predominantly to be affecting homosexual and bisexual men. Soon thereafter, intravenous drug users, hemophiliacs, and recipients of blood transfusions were recognized as being at increased risk for disease as well. It was also noted that sexual partners of persons with AIDS could contract the disease. Further study of AIDS patients revealed marked depletion of certain white BLOOD cells, called T4 lymphocytes. These cells play a crucial role in coordinating the body's immune defenses against invading organisms. It was presumed that this defect in AIDS patients was acquired in a common manner. Then, in 1983, a virus that attacks T4 cells was separately discovered by Robert Gallo at the U.S. National Institutes of Health and Luc Montagnier at France's Pasteur Institute. The virus was at first given various names: human lymphotropic virus (HTLV) III, lymphadenopathy-associated virus (LAV), and AIDS-associated retrovirus (ARV). It is now officially called human immunodeficiency virus (HIV), and considerable...
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