HIV is a virus that causes AIDS by attacking the immune system. It can be transmitted through unprotected sex, sharing needles, unsafe blood transfusions, and from mother to child during pregnancy, birth, or breastfeeding. While HIV itself may not cause symptoms for years, it is diagnosed through blood tests detecting antibodies or the virus. As the virus destroys immune cells over time, it leaves the body vulnerable to opportunistic infections defining AIDS. Though there is no cure for HIV/AIDS, antiretroviral treatment can suppress the virus and prevent opportunistic infections, allowing people to live long and healthy lives.