Ebola Hemorrhagic Fever: Fact Sheet
What is Ebola hemorrhagic fever?
Ebola hemorrhagic fever (Ebola HF) is a severe, often-fatal disease in
humans and nonhuman primates (monkeys and chimpanzees) that has appeared
sporadically since its initial recognition in 1976.
The disease is caused by infection with Ebola virus, named after a river in
the Democratic Republic of the Congo (formerly Zaire) in Africa, where it was
first recognized. The virus is one of two members of a family of RNA viruses
called the Filoviridae. Three of the four species of Ebola virus identified so
far have caused disease in humans: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory
Coast. The fourth, Ebola-Reston, has caused disease in nonhuman primates, but
not in humans.
Where is Ebola virus found in nature?
The exact origin, locations, and natural habitat (known as the "natural
reservoir") of Ebola virus remain unknown. However, on the basis of
available evidence and the nature of similar viruses, researchers believe that
the virus is zoonotic (animal-borne) and is normally maintained in an animal
host that is native to the African continent. A similar host is probably
associated with Ebola-Reston isolated from infected cynomolgous monkeys that
were imported to the United States and Italy from the Philippines. The virus is
not known to be native to other continents, such as North America.
Where do cases of Ebola hemorrhagic fever occur?
Confirmed cases of Ebola HF have been reported in the Democratic Republic of
the Congo, Gabon, Sudan, the Ivory Coast, and Uganda. An individual with
serologic evidence of infection but showing no apparent illness has been
reported in Liberia, and a laboratory worker in England became ill as a result
of an accidental needle-stick. No case of the disease in humans has ever been
reported in the United States. Ebola-Reston virus caused severe illness and
death in monkeys imported to research facilities in the United States and Italy
from the Philippines; during these outbreaks, several research workers became
infected with the virus, but did not become ill.
Ebola HF typically appears in sporadic outbreaks, usually spread within a
health-care setting (a situation known as amplification). It is likely that
sporadic, isolated cases occur as well, but go unrecognized. A table
showing a chronological list of known cases and outbreaks is available
How is Ebola virus spread?
Infection with Ebola virus in humans is incidental -- humans do not
"carry" the virus. Because the natural reservoir of the virus is
unknown, the manner in which the virus first appears in a human at the start of
an outbreak has not been determined. However, researchers have hypothesized
that the first patient becomes infected through contact with an infected
After the first case-patient in an outbreak setting (often called the index
case) is infected, humans can transmit the virus in several ways. People can be
exposed to Ebola virus from direct contact with the blood and/or secretions of
an infected person. This is why the virus has often been spread through the
families and friends of infected persons: in the course of feeding, holding, or
otherwise caring for them, family members and friends would come into close
contact with such secretions. People can also be exposed to Ebola virus through
contact with objects, such as needles, that have been contaminated with