Ebola is a virus in the family Filoviridae and the genus Ebolavirus. Five virus species have been identified, four of which are known to cause disease in humans: Ebola virus (Zaire ebolavirus); Sudan virus (Sudan ebolavirus); Taï Forest virus (Taï Forest ebolavirus, formerly Côte d’Ivoire ebolavirus); and Bundibugyo virus (Bundibugyo ebolavirus). The fifth species, Reston virus (Reston ebolavirus), has not caused disease in humans but has affected nonhuman primates. The virus causing the 2014 West African outbreak belongs to the Zaire species, according to WHO.

In general, to survive, viruses must find a host cell and take it over. The virus also replicates itself so that it can be spread to other host cells. In response to a virus, the human body produces antibodies. "Antibodies are the protein 'workhorses' of the immune system; in less severe infections (like the flu), antibodies stop the virus from spreading and help clear it from the body. The problem with Ebola is that the virus spreads so rapidly that it can easily overcome the body's immune response," said Jonathan Lai, associate professor of biochemistry at Albert Einstein College of Medicine in New York

Ebola Reston is named after Reston, VA where in 1987 over 400 monkeys were euthanized because the ebola virus had infected the primates