Viruses are the smallest and simplest type of parasite. They enter the body and take over a living cell just to reproduce. When these viruses do take over these cells, they may cause great damage or even completely kill the invaded cell.
AIDS, which stands for Acquired Immunodeficiency Syndrome, is caused by a lethal virus called Human Immunodeficiency Virus, or better known to everybody as HIV. HIV is a fragile virus because it can live outside the human body for only a few minutes. Most regularly, the virus is found in blood, semen, and vaginal secretions of the infected people. However, saliva and tears contain much lower concentrations. Most people think that they can not get HIV, but as we have seen in Magic Johnson's case, even famous celebrities can get this disease. To get infected, HIV has to get past the skin or the mucous membranes and into the bloodstream.
HIV causes the body's immune system to collapse the moment that the bloodstream is infected.
To Understand how HIV weakens the immune system, it is necessary to understand how the immune system works. The immune system is somewhat similar to an army. Thousands of white blood cells are highly organized to fight invading enemies such as the HIV virus and other such infections. White blood cells circulate through the bloodstream and the lymphatic system. The lymphatic system is a network of vessels and lymph glands that collect fluid and cells from tissues and deliver them to the bloodstream. The white blood cells can leave the blood vessels, travel between cells, enter the lymphatic system, and eventually return to the bloodstream. These cells patrol the body, searching for foreign invaders and attacking any they find.
When invaders like HIV infect the body, white blood cells called helper T cells...