ABSTRACT

The human immunodeficiency virus (HIV) is a disease that attacks the human immune system. Once infected, a person’s immune system deteriorates over a number of years, until it is incapable of resisting infections. At this stage, clinically defined by a low CD4 cell count (below 200 cells/mm) or by an AIDS-defining illness, the person has AIDS (acquired immune deficiency syndrome). HIV infection is transmitted through the exchange of body fluids, including semen, vaginal secretions, blood and breast milk. Worldwide, most people contract HIV from sexual contact, although needle-sharing, blood transfusions and breastfeeding are also responsible for large numbers of infections.