Human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS) are names for different stages of the same viral infection that impairs a person’s immune system. This infection attacks the cells that coordinate a person’s immune response to foreign invaders and prevents the body from fighting off viruses, bacteria, fungi and parasites.

People become infected with the HIV virus through contact with certain types of body fluids from an infected individual. After infection, the virus begins to quietly damage the immune system by invading helper T cells (CD4 lymphocytes), the white blood cells that coordinate the immune system. Eventually all people with HIV will go on to develop AIDS. However, it can take a decade or more before HIV develops into full-blown AIDS. Many of the available treatments, if initiated early enough, can help delay this progression.

People with HIV or AIDS are more likely to contract certain conditions known as opportunistic infections. These are diseases that may be rare in people with healthy immune systems but can be life-threatening in people with HIV or AIDS. 

Though there is no cure for HIV and AIDS, treatments have become much more effective in controlling symptoms and suppressing disease progression in recent years. Today, people with AIDS can lengthen their lifespan and enhance their quality of life through a variety of medications. Most people in the United States and other developed nations have access to these drugs. In developing parts of the world, access is limited, and AIDS mortality rates remain high.