The human immunodeficiency virus (HIV) was first detected in 1981 and has been claiming lives since then all over the world. The virus causes an infectious disease that, if left untreated, rapidly develops into acquired immunodeficiency syndrome (AIDS). People often use the abbreviations HIV and AIDS interchangeably, but there is a definite progression. HIV infection comes first and AIDS is the last stage of the disease. A small percentage of those testing positive for HIV remain unaffected by the disease and do not develop AIDS. They are known as "non-progressors." In most people HIV progresses to AIDS, and AIDS is still incurable and invariably fatal. The progression to AIDS can be slowed but not yet prevented.
HIV interferes with and ultimately blocks the body's immune system. Infected people have a reduced count of a crucial blood cell called CD4 lymphocyte. When CD4 is present, it prevents the onset of many fatal infections and cancers. In HIV-negative healthy people the CD4 count is between 500 and 1,500 cells per cubic millimeter of blood. CD4 counts below 350 may signal HIV infection; levels below 200 are considered to indicate the presence of AIDS ("AIDS," MEDLINEplus, a service of the National Library of Medicine and the National Institutes of Health, http://www.nlm.nih.gov/medlineplus/ency/article/000594.htm).
Only a test administered by a qualified health professional can absolutely diagnose HIV infection. In addition to having one or more opportunistic infections (bacterial, fungal, protozoal, and viral agents that take advantage of an immune system weakened by HIV), infected individuals also have other symptoms. They may experience a general malaise, weight loss, nausea, fever, night sweats, swollen lymph glands, persistent cough, unexplained bleeding, watery diarrhea, loss of memory, balance problems, mood changes, blurring or loss of vision, and thrush (a white coating of the tongue and throat). Individuals who die of AIDS die of opportunistic infections and cancers, not of the virus; the effect of the virus is to weaken their bodily defenses.