HIV is transmitted through the exchange of certain body fluids from a person living with HIV, including blood, semen, vaginal fluids, rectal fluids, and breast milk. The main modes of transmission are unprotected sexual intercourse, sharing contaminated needles or syringes, mother-to-child transmission during pregnancy, childbirth, or breastfeeding, and transfusion of infected blood where blood screening is not available. HIV is not transmitted through casual contact such as hugging, shaking hands, sharing food, or mosquito bites.