In recent years, the number of opportunistic infections known to be associated with AIDS has grown. Also, as scientists came to recognize how HIV affects the human body, an additional defining feature of AIDS based on the health of the person's immune system was added to a physician's diagnostic guide. Prior to the discovery of new treatments for AIDS, most people who were infected with HIV eventually developed full blown AIDS and most of these individuals died of this disease. However, there are some strains of HIV that are not as lethal as others, and scientists are attempting to understand variation in the virus and the ability of the immune system to respond to viral infection. As the name HIV implies, the disease is known to be caused by a specific virus.
Viruses are a curious type of phenomenon.
In a sense, they are only partial organisms in that they must live inside another organism or host. Otherwise they are dormant. Moreover, their entire existence is focused on spreading from one host to another and on reproducing themselves. When HIV enters a human body, it tends to seek out and attack a particular group of white blood cells commonly known as the T-helper cells. These cells are part of the body's immune system.