Named after the Ebola River Valley in the Democratic Republic of Congo, where the first outbreak occurred, this deadly hemorrhagic fever is caused by a group of viruses (shown here) that belong to the genus Ebolavirus.

Though mostly confined to African countries, the disease came to the United States in 1989 when a new strain was discovered in crab-eating macaques imported from the Philippines to Reston, Virginia. Several outbreaks caused by the Reston strain have occurred in Texas, Pennsylvania, and Italy. Of the 1,850 or so patients that have been afflicted by the disease since it was first discovered, over 1,200 have died.

The virus attacks the host's endothelial cells and platelet cells, damaging both and preventing the latter from coagulating. As a result, victims lose large amounts of blood and eventually collapse and die from shock.