Causes: Human immunodeficiency virus (HIV) causes AIDS . The virus attacks the immune system and leaves the body vulnerable to a variety of life-threatening infections and cancers. Common bacteria, yeast, parasites, and viruses that ordinarily do not cause serious disease in people with healthy immune systems can cause fatal illnesses in people with AIDS . HIV has been found in saliva, tears, nervous system tissue and spinal fluid, blood, semen (including pre-seminal fluid, which is the liquid that comes out before

ejaculation), vaginal fluid, and breast milk. However, only blood, semen, vaginal secretions, and breast milk generally transmit infection to others.

The virus can be spread (transmitted):

Through sexual contact -- including oral, vaginal, and anal sex.

Through blood -- via blood transfusions (now extremely rare in the U.S.) or needle sharing.

From mother to child -- a pregnant woman can transmit the virus to her fetus through their shared blood circulation, or a nursing mother can transmit it to her baby in her breast milk.

Other methods of spreading the virus are rare and include accidental needle injury, artificial insemination with infected donated semen, and organ transplantation with infected organs.

HIV infection is NOT spread by: Casual contact such as hugging, Mosquitoes, Participation in sports and Touching items previously touched by a person infected with the virus.

AIDS and blood or organ donation:

AIDS is NOT transmitted to a person who DONATES blood or organs. Those who donate organs are never in direct contact with those who receive them. Likewise, a person who donates blood is not in contact with the person receiving it. In all these procedures, sterile needles and instruments are used.

However, HIV can be transmitted to a person RECEIVING blood or organs from an infected donor. To reduce this risk, blood banks and organ donor programs screen donors, blood, and tissues thoroughly.

People at highest risk for getting HIV include: Injection drug users who share needles, Infants born to mothers with HIV who didn't receive HIV therapy during pregnancy, People engaging in 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 participate in high-risk activities (such as injection drug use or anal sex).