AIDS (Acquired Immunodeficiency Syndrome) is a chronic disease caused by the Human Immunodeficiency Virus (HIV). The HIV virus attacks and gradually destroys CD4+ T-lymphocytes, which are the cells in the human immune system responsible for fighting infections. When the immune system is severely damaged (typically defined as a CD4 cell count falling below 200 cells per cubic millimetre), the individual progresses to the AIDS stage, becoming highly susceptible to various “opportunistic infections” or cancers, which pose a serious threat to life.