Ebola hemorrhagic fever is a disease with a high fatality rate. It most commonly affects people and nonhuman primates such as monkeys, gorillas and chimpanzees. The fever is caused by an infection with one of five known Ebola virus species. Four of the strains can cause severe illness in humans and animals. The current outbreak in Congo is due to the Zaire ebolavirus, which has the highest mortality rate. Ebola is named after the Ebola River in what is now the Democratic Republic of Congo. The virus was first recognized in 1976, according to the US Centers for Disease Control and Prevention.