Ebola virus disease (EVD) was first identified in 1976 following simultaneous outbreaks in Sudan and Zaire (now the Democratic Republic of Congo, or DRC) in Africa.1 Though both outbreaks were attributed at the time to the same virus, two separate viruses were later identified as having caused the respective outbreaks: Sudan Ebola virus (SUDV) and Zaire Ebola virus (EBOV). EVD, and subsequently the EBOV strain, was named after the Ebola River in Zaire near the village where it was isolated.2
EVD results from infection with viral species in the Ebolavirus genus of the family Filoviridae, including EBOV, SUDV, and Bundibugyo Ebola virus (BDBV). Two additional species, Reston Ebola virus (RESTV) and Côte d’Ivoire or Taï Forest Ebola virus (TAFV) are included in the genus, but are not known to cause outbreaks among humans.
In the 20 years following the initial outbreak of EBOV and SUDV, scientists identified the three additional species of Ebola viruses. RESTV was found in Cynomolgus monkeys (crab-eating macaques) at an animal quarantine facility in Reston, Virginia, in 1989.3 The monkeys were imported from the Philippines, where RESTV now appears to be endemic. Several workers who had contact with monkeys and pigs with RESTV infections developed laboratory-identified subclinical (asymptomatic) infections.2 TAFV was isolated from a veterinary researcher who had performed a necropsy on a chimpanzee that died of EVD. The researcher is the only known human case of TAFV-attributable EVD. The final known species, BDBV, caused a small outbreak among humans in western Uganda in 2007.4
Though Ebola viruses have caused outbreaks in humans, non-human primates, and pigs, the natural host of the pathogen is unknown. Antibody testing research suggests that bats may be a reservoir.5
1 Heinz Feldmann and Thomas Geisbert, "Ebola haemorrhagic fever." The Lancet 377, no. 7968 (2011), 849-862, http://dx.doi.org/10.1016/S0140-6736 (10)60667-8.
2 "Ebola Virus Disease," World Health Organization (WHO).
3 Heinz Feldmann and Hans-Dieter Klenk, "Filoviruses," in Medical Microbiology, 4th edition, ed. S. Baron (Galveston, TX: University of Texas Medical Branch at Galveston, 1996).
4 Jonathan S. Towner, Tara K. Sealy, Marina L. Khristova, César G. Albariño, Sean Conlan, Serena A. Reeder, et al., "Newly Discovered Ebola Virus Associated with Hemorrhagic Fever Outbreak in Uganda," PLoS Path 4, no. 11 (2008).
5 Kevin J. Olival, Ariful Islam, Meng Yu, Simon J. Anthony, Jonathan H. Epstein, Shahneaz Ali Khan, Salah Uddin Khan, et al., "Ebola virus antibodies in fruit bats, Bangladesh," Emerging Infectious Diseases 19, no. 2 (2013), 270.