The organism that causes AIDS is HIV. CD4 cells, which help the body fight disease, are destroyed when HIV develops into AIDS.
The first case of HIV was reported in humans in what is now known as the Democratic Republic of Congo in 1959. In 1984, Dr. Robert Gallo discovered that HIV is the organism that actually causes AIDS. By 1994, AIDS was the leading cause of death in the United States for those between the ages of 25 to 44. While there is no cure for AIDS as of 2015, there are several different treatment options available that greatly extend the lives of those affected with it.