Human Immunodeficiency Virus (HIV) is the virus that causes Acquired Immune Deficiency Syndrome (AIDS.) HIV affects a person’s immune system, the body’s natural defense against disease. The only way to become infected with HIV is through contact with blood or other body fluids like semen or vaginal fluid from someone who has the HIV virus. HIV is usually transmitted through unprotected sex or by using needles or syringes used by someone with HIV. It can also be passed from an infected pregnant mother to her fetus. There is no cure for HIV. When left untreated, HIV can turn into AIDS. With proper treatment, people diagnosed with AIDS can maintain a relatively healthy life. But without treatment, AIDS is fatal.