Ebola is a good example of an emergent disease. A viral hemorrhagic fever, Ebola is extremely contagious and three of the five varieties of the virus are exceedingly lethal, typically killing up to 90 percent of those who become infected. The disease was unknown in humans until the mid-1980s. The increased interaction between humans and primates, principally due to poaching along with the killing and eating of chimps, gorillas, and other primates is thought to have spurred the virus to cross the primate-human barrier.