AIDS
(Acquired immune deficiency syndrome) AIDS, first described in 1981, is caused by a virus that not only damages tissues, but also increases vulnerability to many disorders, especially infections. These result from the progressive destruction of the immune system by the human immunodeficiency virus (HIV). The virus is transmitted when a body fluid of an infected individual-blood, semen, vaginal secretion, or breast milk-is absorbed into the blood-stream of a healthy person. The major exception appears to be saliva, which has never been shown to be a carrier.
When the disease was first discovered in the United States, most cases were transmitted by male homosexual activity, in contrast to the underdeveloped nations, where AIDS was spread mostly through heterosexual intercourse. Now most cases in the U.S. are transmitted by the sharing of hypodermic needles and heterosexual intercourse, with women accounting for a large percentage of new cases. Before development of an HIV screening test in 1986, a number of cases were contracted from contaminated transfusions and the coagulation factors used to treat hemophilia.
Whenever a virus enters the body, a healthy immune system produces a variety of fighter cells, which include the T-cell lymphocytes. HIV invades T-cells and uses their genetic material to multiply itself. The virus eventually destroys the T-cells, producing many new HIV particles in the process. In time, the immune system is over-whelmed by the infection, and the person becomes increasingly susceptible to the infections and other disease that make up the AIDS complex.
It takes an average of 10 years from the time of infection to develop full-blown AIDS, and throughout that entire period, contact with body fluids from the person harboring the virus can spread the infection.






