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Ebola is a rare and often fatal illness caused by viruses of the family Filoviridae, genus Ebolavirus, which has five viruses: Ebola virus (EBOV), Sudan virus, Bundibugyo virus, Taï Forest virus, and Reston virus. All viruses cause disease in humans except Reston virus, which has caused asymptomatic infections in humans but disease in nonhuman primates only. The natural wildlife host of EBOV has not been definitively identified; however, evidence suggests fruit bats of the family Pteropodidae might be a reservoir. Ebola was first recognized in 1976 during two near-simultaneous outbreaks: one caused by EBOV in Zaire (now Democratic Republic of the Congo [DRC]) that comprised 318 cases and 280 deaths (case-fatality rate [CFR] = 88%), and the other caused by Sudan virus in Sudan that comprised 284 cases and 151 deaths (CFR = 53%). These and subsequent sporadic outbreaks of Ebola in Eastern and Central African nations (DRC, seven; Uganda, five; Gabon, four; and Republic of the Congo and Sudan [now South Sudan], three each) had CFRs of approximately 25%–90%; occurred in resource-poor settings where health care, transportation, and other services are limited; and lasted from several weeks to approximately 3 months (1) (Table).
EBOV is thought to be introduced into humans when a person has direct contact with blood, body fluids, or organs of infected animals (e.g., fruit bats, chimpanzees, or gorillas) or prepares meat from infected animals. Infection in human communities is sustained through person-to-person contact, often from symptomatic persons to caregivers in homes and health care settings, where infection-control practices are inadequate and personal protective equipment is unavailable or in short supply. In some previous outbreaks (e.g., Kikwit, Zaire, in 1995), the infection cycle was amplified by explosive spread of disease in overcrowded local hospitals, underscoring the role of nosocomial transmission. Because corpses have high viral loads, funerals and burials accompanied by ceremonial washing and touching of deceased persons often are responsible for multiple chains of transmission.
During the first reported Ebola outbreak in Zaire in 1976, an international response team developed an early strategy to stop the outbreak, focusing on the identification, isolation, and care of persons with Ebola symptoms; meticulous contact tracing; engagement with community leaders; culturally sensitive and safe burials; effective infection control; and reliable laboratory testing (2). This strategy, further refined with accumulated experience, has been used to successfully control approximately 20 Ebola outbreaks, including DRC’s seventh outbreak in November 2014 (3).
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