HIV: HIV (human immunodeficiency virus) and AIDS (acquired immune deficiency syndrome) is range of conditions caused when infected by the virus HIV. The HIV virus destroys a type of white blood cell in the immune system called a T-helper cell, and makes copies of itself inside these cells. If HIV is left untreated, it may take up to 10 or 15 years for the immune system to be so severely damaged it can no longer defend itself at all. However, the speed HIV progresses will vary depending on age, health and background.