Luckily, Level 4 epidemics are rare. The Ebola virus was last diagnosed in 1976 in Sudan and Zaire. It killed more than 400 of its 600 victims. However, Level 4 viruses are not limited to remote regions of the world - the hantavirus outbreak in 1993 in the southwestern United States killed more than 100 people. The virus attacked the lungs.
Blood vessels leak and are no longer able to carry blood to organs.
The victims bleed from the nose, ears, mouth and eyes. For many, it is a very slow and painful death. The virus runs its course in about a week. For every 10 patients with Ebola, seven die. Viruses are difficult, and often impossible, to treat because they mutate quickly.