AIDS (Acquired immune deficiency syndrome or acquired immunodeficiency syndrome) is a syndrome caused by a virus called HIV (Human Immunodeficiency Virus). Human immunodeficiency virus (HIV), HIV-1 or HIV-2, are blood-borne retroviruses in the Retroviridae family, Lentivirus genus. HIV attacks the immune system, making people much more vulnerable to infections and diseases. The virus is passed from one person to another through blood-to-blood and sexual contact. In addition, infected pregnant women can pass HIV to their babies during pregnancy, delivering the baby during childbirth, and through breast feeding.