human immunodeficiency virus (HIV)

The acquired immune deficiency syndrome (AIDS) virus, which attacks the body's immune system and thereby leaves the HIV-infected person vulnerable to a debilitating or fatal opportunistic infection, cancer, or neurological condition. Two types of HIV have been identified: HIV 1 is found worldwide and HIV 2 appears mainly in central Africa. The progression of infection is similar. Blood, semen, vaginal secretions, and breast milk have been implicated in transmission. HIV is transmitted by unprotected penetrative sexual intercourse with an infected person, by infected hypodermic needles, by medical transfusion of untreated blood, and from infected mother to child (in utero, during birth, or shortly after birth). HIV cannot be transmitted casually through, for example, touching an infected person or sharing a drinking glass. HIV infection and infectiousness are presumed to be lifelong.