HIV is a virus that attacks the body’s immune system, the system that helps the body fight disease. There are medical tests to tell if a person has the virus in his or her body and we then say that person is HIV positive. The virus is too small to see, but can multiply quickly and the greater the quantity of virus in the blood, the more likely the person is to get sick with some other illness like flu, TB, diarrhoea and other infections. AIDS is the serious disease caused by the HIV virus.