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 subtypes 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 the Ebola-Reston virus subtype 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, and the Ivory Coast. 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.
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 animal. After the first case-patient in an outbreak
setting (often called the index case) is infected, the virus can be transmitted 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...