Ebola virus disease is one of the most lethal and feared diseases in the modern world even though the total number of people harmed by it throughout history is, fortunately, far smaller than for better known scourges such as malaria and influenza. Among individuals who contract this disease, the fatality rate averages approximately 50 percent, although it can reach as high as 90 percent. Outbreaks of this highly infectious disease are therefore of great concern to infected communities and medical personnel, especially when the populations at risk are large. The disease arises from infection with one of the Ebola virus strains, which comprise a group of exotic viral agents that cause a severe hemorrhagic fever in humans and other primates. The virus is spread through human-to-human transmission and requires direct contact with the bodily fluids or blood of an infected person. It also can be transmitted via surfaces and objects that have been contaminated with these fluids. Airborne transmission does not occur. (Other types of hemorrhagic diseases caused by RNA viruses include dengue fever, hantavirus pulmonary syndrome, Lassa fever, and yellow fever, many of which are transmitted by insects and rodents rather than by direct contact.) See also: Ebola virus; Epidemiology; Exotic viral diseases; Hantavirus outbreak; Infectious disease; Virus; Virus classification

Ebola was first recognized and reported in southern Sudan (now South Sudan) and the Democratic Republic of the Congo (formerly Zaire) in 1976. The latter country is also the locale of the Ebola River, from which the name of the disease is derived. Since 1976, sporadic outbreaks have occurred predominantly in Central Africa (Uganda, South Sudan, Gabon, and the Democratic Republic of the Congo), but these outbreaks were very limited in scope and were contained within their localities. Those outbreaks typically affected at most a few dozen individuals, although some very rare occurrences of the disease led to the infection and deaths of a few hundred individuals. See also: Africa; Disease ecology

The Ebola epidemic that started in March 2014 and continued through 2015 killed more than 11,300 persons. This outbreak was centered in West Africa, an area that had not been affected by the disease previously. The toll was particularly grave in three countries: Guinea, Liberia, and Sierra Leone. In early 2016, though, the three affected countries were declared free of Ebola virus transmission, allowing the World Health Organization to consider the epidemic to be over. Still, isolated outbreaks are predicted because of the virus persisting in survivors after recovery (in fact, one death occurred in Sierra Leone shortly after the World Health Organization declared an end to the epidemic), so strict control measures need to remain in effect. In addition, a few cases were reported in countries outside of West Africa during the most deadly months of the epidemic, all related to international travelers who were exposed in the most affected regions and later showed symptoms of Ebola fever after reaching their destinations. There also have been a handful of cases of health-care workers who contracted the disease in their home countries from patients infected in West Africa. These new transmissions in places far outside the primary zones of infection have stirred a worldwide awareness of the Ebola virus and a challenge to combat the disease more effectively and with more resources. No vaccine or antiviral drug is yet available to fight Ebola, but some experimental treatments have shown promise. In general, individuals with Ebola need dependable and high-quality supportive care in their attempts at recovery. Infected individuals also need to be isolated properly to prevent any spreading of the disease. Constant monitoring of all patients and health-care personnel is vital. See also: Epidemic; Public health; Vaccination