Fact Sheet N°
Revised December 2000
EBOLA HAEMORRHAGIC FEVER
Ebola haemorrhagic fever (EHF) is one of the most
virulent viral diseases known to humankind, causing death in 50-90% of all
clinically ill cases. The disease has its origins in the jungles of Africa
and Asia. Several different forms of Ebola virus have been identified and
may be associated with other clinical expressions, on which further
research is required.
- The Ebola virus is transmitted by direct contact with the blood,
secretions, organs or semen of infected persons. Transmission through
semen may occur up to seven weeks after clinical recovery, as with
Marburg haemorrhagic fever.
- Transmission of the Ebola virus has also occurred by handling ill or
dead infected chimpanzees, as was documented in Côte d'Ivoire and
- Health care workers have frequently been infected while attending
patients. In the 1976 epidemic in Zaire, every Ebola case caused by
contaminated syringes and needles died.
Incubation: 2 to 21 days
Symptoms: Ebola is often characterized by the
sudden onset of fever, weakness, muscle pain, headache and sore throat.
This is followed by vomiting, diarrhoea, rash, limited kidney and liver
functions, and both internal and external bleeding.
Diagnosis: Commercially unavailable specialized
laboratory tests on blood specimens detect specific antigens and/or genes
of the virus, isolate the virus in cell culture or detect IgM and IgG
antibodies. These tests present an extreme biohazard and are only
conducted under maximum biological containment conditions.
- No specific treatment or vaccine exists for Ebola haemorrhagic
- Severe cases require intensive supportive care, as patients are
frequently dehydrated and in need of intravenous fluids.
- Experimental studies involving the use of hyper-immune sera on
animals demonstrated no long-term protection against the disease after
interruption of therapy.
- Suspected cases should be isolated from other patients and strict
barrier nursing techniques practised.
- All hospital personnel should be briefed on the nature of the
disease and its routes of transmission. Particular emphasis should be
placed on ensuring that high-risk procedures such as the placing of
intravenous lines and the handling of blood, secretions, catheters and
suction devices are carried out under barrier nursing conditions.
Hospital staff should have individual gowns, gloves and masks. Gloves
and masks must not be reused unless disinfected.
- Patients who die from the disease should be promptly buried or
- As the primary mode of person-to-person transmission is contact with
contaminated blood, secretions or body fluids, any person who has had
close physical contact with patients should be kept under strict
surveillance, i.e. body temperature checks twice a day, with immediate
hospitalization and strict isolation recommended in case of
temperatures above 38.3°C (101°F). Casual contacts should be placed
on alert and asked to report any fever.
- Surveillance of suspected cases should continue for three weeks
after the date of their last contact.
- Hospital personnel who come into close contact with patients or
contaminated materials without barrier nursing attire must be
considered exposed and put under close supervised surveillance.
History and Prevalence
The Ebola virus was first identified in a western
equatorial province of Sudan and in a nearby region of Zaire (now
Democratic Republic of the Congo) in 1976 after significant epidemics in
Yambuku, northern Zaire, and Nzara, southern Sudan.
- Between June and November 1976 the Ebola virus infected 284 people
in Sudan, with 117 deaths. In Zaire, there were 318 cases and 280
deaths in September and October. An isolated case occurred in Zaire in
1977, a second outbreak in Sudan in 1979.
- In 1989 and 1990, a filovirus, named Ebola-Reston, was isolated in
monkeys being held in quarantine in laboratories in Reston (Virginia),
Alice (Texas) and Pennsylvania, United States of America. In the
Philippines, Ebola-Reston infections occurred in the quarantine area
for monkeys intended for exportation, near Manila. Ebola-related
filoviruses were isolated from cynomolgus monkeys (Macacca
fascicularis) imported into the United States of America from the
Philippines in 1989. A number of the monkeys died and at least four
persons were infected, although none of them suffered clinical
- A large epidemic occurred in Kikwit, Zaire in 1995 with 315 cases,
244 of which had fatal outcomes.
- One human case of Ebola haemorrhagic fever and several cases in
chimpanzees were confirmed in Côte d'Ivoire in 1994-95.
- In Gabon, Ebola haemorrhagic fever was first documented in 1994 and
outbreaks occurred in February 1996 and July 1996.
- Ebola virus infections were not reported again until the autumn of
2000 when an outbreak occurred in northern Uganda.
Excluding the most recent outbreak, approximately 1,500 cases
with slightly over 1,000 deaths have been documented since the virus was discovered.
- The natural reservoir of the Ebola virus seems to reside in the rain
forests of Africa and Asia, but has not yet been identified. Different
hypotheses have been developed to try to explain the origin of Ebola
outbreaks. Initially, rodents were suspected, as is the case with Lassa
fever whose reservoir is a wild rodent (Mastomys). Another
hypothesis is that a plant virus may have caused the infection of
vertebrates. Laboratory observation has shown that bats experimentally
infected with Ebola do not die and this has raised speculation that
these mammals may play a role in maintaining the virus in the tropical
- Although non-human primates have been the source of infection for
humans, they are not thought to be the reservoir. They, like humans,
are infected directly from the natural reservoir or through a chain of
transmission from the natural reservoir.
- Extensive ecological studies are currently under way in Côte
d'Ivoire to identify the reservoir of Ebola. Studies to identify the
reservoir of Marburg virus, a closely related filovirus are being
conducted in the Democratic Republic of the Congo.
Please contact the Spokesperson's Office, WHO, Geneva, Tel.: (+41 22) 791
2599, Fax: (+41 22) 791 4858, E-mail: firstname.lastname@example.org
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