Outbreaks in nonhuman primates and antelope often precede, or happen at the same time as, human cases of Ebola Virus Disease (EVD) in the same or nearby areas.
- Before Taï National Forest outbreak (1994), the chimpanzee population in the area decreased by half.
- Before and during Gabon outbreak (2001), 64 dead gorillas, chimpanzees, and antelope were discovered.
Cases of EVD in people typically emerge following the handling and butchering of these infected animals. Once the virus spreads to people, it can spread quickly from person to person within families and other close contacts, as well as in healthcare settings. Rapid identification of cases is critical to prevent large-scale epidemics.
Detection and Response
Prompt identification of cases, contact tracing, and monitoring of high-risk individuals are essential to stopping Ebola virus from spreading.
Early recognition of EVD is critical for infection control. However, because early symptoms are not specific to EVD, it can be hard to distinguish it from other illnesses, including malaria, leptospirosis, influenza (flu), yellow fever, dengue and other viruses spread by insects, or viral or bacterial infections of the intestines, like typhoid fever.
EVD should be considered when clinical illness is combined with an epidemiologic risk factor, like direct contact with a suspected or confirmed case or travel to an Ebola-affected area.
Once a case of EVD is identified, everyone who has come in direct contact with the sick patient is found. This is called contact tracing. Contacts are watched for signs of illness for 21 days from the last day they came in contact with the Ebola patient. If the contact develops a fever or other EVD symptoms, they are immediately isolated, tested, and provided care. Then the cycle starts again until all of the new contacts are found and watched for 21 days. The World Health Organization (WHO) declares an Ebola outbreak over after 42 days (or two incubation periods) have passed without any newly reported infections.
 Kaner J, Schaak S. Understanding Ebola: the 2014 Epidemic. Globalization and Health (2016) 12:53.
 Gonzalez J.P., Herbreteau V, Morvan J, Leroy É.M. Ebola virus circulation in Africa: a balance between clinical expression and epidemiological silence. Bull Soc Pathol Exot, 2005, 98, 3, 210-2017