Human immunodeficiency virus (HIV) causes HIV infection and AIDS. The virus attacks the immune system. As the immune system weakens, the body is at risk of getting life-threatening infections and cancers. Once a person has the virus, it stays inside the body for life. The virus is spread (transmitted) person-to-person in any of the following ways: Through sexual contact -- including oral, vaginal, and anal sex Through blood -- by blood transfusions (now extremely rare in the U.S.) or more often by needle sharing From mother to child -- a pregnant woman can spread the virus to her fetus through their shared blood circulation, or a nursing mother can pass it to her baby through her breast milk The virus is NOT spread by: Casual contact such as hugging Mosquitoes Participating in sports Touching items that were touched by a person infected with the virus HIV and blood or organ donation: HIV is not spread to a person who donates blood or organs. People who donate organs are never in direct contact with people who receive them. Likewise, a person who donates blood is never in contact with the person receiving it. In all these procedures, sterile needles and instruments are used. But HIV can be spread to a person receiving blood or organs from an infected donor. To reduce this risk, blood banks and organ donor programs check (screen) donors, blood, and tissues thoroughly. People at high risk of getting HIV include: Drug users who inject and then share needles Infants born to mothers with HIV who did not receive HIV treatment during pregnancy People who have unprotected sex, especially with people who have other high-risk behaviors, are HIV-positive, or have AIDS People who received blood transfusions or clotting products between 1977 and 1985, before screening for the virus became standard practice Sexual partners of those who engage in high-risk activities (such as injection drug use or anal sex) After HIV infects the body, the virus has been found in many different fluids and tissues in the body. Only blood, semen, fluids from the vagina, and breast milk have been shown to transmit infection to others. The virus may also be found in saliva, tears, nervous system tissue, spinal fluid, and blood.