Key facts
- Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a severe, often fatal illness in humans.
- EVD outbreaks have a case fatality rate of up to 90%.
- EVD outbreaks occur primarily in remote villages in Central and West Africa, near tropical rainforests.
- The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission.
- Fruit bats of the Pteropodidae family are considered to be the natural host of the Ebola virus.
- Severely ill patients require intensive supportive care. No licensed specific treatment or vaccine is available for use in people or animals.
Ebola first
appeared in 1976 in 2 simultaneous outbreaks, in Nzara, Sudan, and in Yambuku,
Democratic Republic of Congo. The latter was in a village situated near the
Ebola River, from which the disease takes its name.
Genus
Ebolavirus is 1 of 3 members of the Filoviridae family (filovirus),
along with genus Marburgvirus and genus Cuevavirus. Genus Ebolavirus comprises
5 distinct species:
- Bundibugyo ebolavirus (BDBV)
- Zaire ebolavirus (EBOV)
- Reston ebolavirus (RESTV)
- Sudan ebolavirus (SUDV)
- Taï Forest ebolavirus (TAFV).
BDBV, EBOV,
and SUDV have been associated with large EVD outbreaks in Africa, whereas RESTV
and TAFV have not. The RESTV species, found in Philippines and the People’s
Republic of China, can infect humans, but no illness or death in humans from
this species has been reported to date.
Transmission
Ebola is
introduced into the human population through close contact with the blood,
secretions, organs or other bodily fluids of infected animals. In Africa,
infection has been documented through the handling of infected chimpanzees,
gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead
or in the rainforest.
Ebola then
spreads in the community through human-to-human transmission, with infection
resulting from direct contact (through broken skin or mucous membranes) with
the blood, secretions, organs or other bodily fluids of infected people, and
indirect contact with environments contaminated with such fluids. Burial
ceremonies in which mourners have direct contact with the body of the deceased
person can also play a role in the transmission of Ebola. Men who have
recovered from the disease can still transmit the virus through their semen for
up to 7 weeks after recovery from illness.
Health-care
workers have frequently been infected while treating patients with suspected or
confirmed EVD. This has occurred through close contact with patients when
infection control precautions are not strictly practiced.
Among
workers in contact with monkeys or pigs infected with Reston ebolavirus,
several infections have been documented in people who were clinically
asymptomatic. Thus, RESTV appears less capable of causing disease in humans
than other Ebola species.
However, the
only available evidence available comes from healthy adult males. It would be
premature to extrapolate the health effects of the virus to all population
groups, such as immuno-compromised persons, persons with underlying medical
conditions, pregnant women and children. More studies of RESTV are needed
before definitive conclusions can be drawn about the pathogenicity and virulence
of this virus in humans.
Signs and symptoms
EVD is a
severe acute viral illness often characterized by the sudden onset of fever,
intense weakness, muscle pain, headache and sore throat. This is followed by
vomiting, diarrhoea, rash, impaired kidney and liver function, and in some
cases, both internal and external bleeding. Laboratory findings include low
white blood cell and platelet counts and elevated liver enzymes.
People are
infectious as long as their blood and secretions contain the virus. Ebola virus
was isolated from semen 61 days after onset of illness in a man who was
infected in a laboratory.
The
incubation period, that is, the time interval from infection with the virus to
onset of symptoms, is 2 to 21 days.
Diagnosis
Other
diseases that should be ruled out before a diagnosis of EVD can be made
include: malaria, typhoid fever, shigellosis, cholera, leptospirosis, plague,
rickettsiosis, relapsing fever, meningitis, hepatitis and other viral
haemorrhagic fevers.
Ebola virus
infections can be diagnosed definitively in a laboratory through several types
of tests:
- antibody-capture enzyme-linked immunosorbent assay (ELISA)
- antigen detection tests
- serum neutralization test
- reverse transcriptase polymerase chain reaction (RT-PCR) assay
- electron microscopy
- virus isolation by cell culture.
Samples from
patients are an extreme biohazard risk; testing should be conducted under
maximum biological containment conditions.
Vaccine and treatment
No licensed
vaccine for EVD is available. Several vaccines are being tested, but none are
available for clinical use.
Severely ill
patients require intensive supportive care. Patients are frequently dehydrated
and require oral rehydration with solutions containing electrolytes or
intravenous fluids.
No specific
treatment is available. New drug therapies are being evaluated.
Natural host of Ebola virus
In Africa,
fruit bats, particularly species of the genera Hypsignathus monstrosus,
Epomops franqueti and Myonycteris torquata, are considered possible
natural hosts for Ebola virus. As a result, the geographic distribution of
Ebolaviruses may overlap with the range of the fruit bats.
Ebola virus in animals
Although
non-human primates have been a source of infection for humans, they are not thought
to be the reservoir but rather an accidental host like human beings. Since
1994, Ebola outbreaks from the EBOV and TAFV species have been observed in
chimpanzees and gorillas.
RESTV has
caused severe EVD outbreaks in macaque monkeys (Macaca fascicularis) farmed in
Philippines and detected in monkeys imported into the USA in 1989, 1990 and
1996, and in monkeys imported to Italy from Philippines in 1992.
Since 2008,
RESTV viruses have been detected during several outbreaks of a deadly disease
in pigs in People’s Republic of China and Philippines. Asymptomatic infection
in pigs has been reported and experimental inoculations have shown that RESTV
cannot cause disease in pigs.
Prevention and control
Controlling Reston ebolavirus in domestic animals
No animal
vaccine against RESTV is available. Routine cleaning and disinfection of pig or
monkey farms (with sodium hypochlorite or other detergents) should be effective
in inactivating the virus.
If an
outbreak is suspected, the premises should be quarantined immediately. Culling
of infected animals, with close supervision of burial or incineration of
carcasses, may be necessary to reduce the risk of animal-to-human transmission.
Restricting or banning the movement of animals from infected farms to other areas
can reduce the spread of the disease.
As RESTV
outbreaks in pigs and monkeys have preceded human infections, the establishment
of an active animal health surveillance system to detect new cases is essential
in providing early warning for veterinary and human public health authorities.
Reducing the risk of Ebola infection in people
In the
absence of effective treatment and a human vaccine, raising awareness of the
risk factors for Ebola infection and the protective measures individuals can
take is the only way to reduce human infection and death.
In Africa,
during EVD outbreaks, educational public health messages for risk reduction
should focus on several factors:
- Reducing the risk of wildlife-to-human transmission from contact with infected fruit bats or monkeys/apes and the consumption of their raw meat. Animals should be handled with gloves and other appropriate protective clothing. Animal products (blood and meat) should be thoroughly cooked before consumption.
- Reducing the risk of human-to-human transmission in the community arising from direct or close contact with infected patients, particularly with their bodily fluids. Close physical contact with Ebola patients should be avoided. Gloves and appropriate personal protective equipment should be worn when taking care of ill patients at home. Regular hand washing is required after visiting patients in hospital, as well as after taking care of patients at home.
- Communities affected by Ebola should inform the population about the nature of the disease and about outbreak containment measures, including burial of the dead. People who have died from Ebola should be promptly and safely buried.
Pig farms in
Africa can play a role in the amplification of infection because of the
presence of fruit bats on these farms. Appropriate biosecurity measures should
be in place to limit transmission. For RESTV, educational public health
messages should focus on reducing the risk of pig-to-human transmission as a
result of unsafe animal husbandry and slaughtering practices, and unsafe
consumption of fresh blood, raw milk or animal tissue. Gloves and other
appropriate protective clothing should be worn when handling sick animals or
their tissues and when slaughtering animals. In regions where RESTV has been
reported in pigs, all animal products (blood, meat and milk) should be
thoroughly cooked before eating.
Controlling infection in health-care settings
Human-to-human
transmission of the Ebola virus is primarily associated with direct or indirect
contact with blood and body fluids. Transmission to health-care workers has
been reported when appropriate infection control measures have not been
observed.
It is not
always possible to identify patients with EBV early because initial symptoms
may be non-specific. For this reason, it is important that health-care workers
apply standard precautions consistently with all patients – regardless of their
diagnosis – in all work practices at all times. These include basic hand
hygiene, respiratory hygiene, the use of personal protective equipment
(according to the risk of splashes or other contact with infected materials),
safe injection practices and safe burial practices.
Health-care
workers caring for patients with suspected or confirmed Ebola virus should
apply, in addition to standard precautions, other infection control measures to
avoid any exposure to the patient’s blood and body fluids and direct
unprotected contact with the possibly contaminated environment. When in close
contact (within 1 metre) of patients with EBV, health-care workers should wear
face protection (a face shield or a medical mask and goggles), a clean,
non-sterile long-sleeved gown, and gloves (sterile gloves for some procedures).
Laboratory
workers are also at risk. Samples taken from suspected human and animal Ebola
cases for diagnosis should be handled by trained staff and processed in
suitably equipped laboratories.
Standard
precautions are recommended in the care and treatment of all patients
regardless of their perceived or confirmed infectious status. They include the
basic level of infection control—hand hygiene, use of personal protective
equipment to avoid direct contact with blood and body fluids, prevention of
needle stick and injuries from other sharp instruments, and a set of
environmental controls.
Table: Chronology of previous Ebola virus disease
outbreaks
|
Year
|
Country
|
Ebolavirus
species
|
Cases
|
Deaths
|
Case
fatality
|
|
|
2012
|
Democratic
Republic of Congo
|
Bundibugyo
|
57
|
29
|
51%
|
|
|
2012
|
Uganda
|
Sudan
|
7
|
4
|
57%
|
|
|
2012
|
Uganda
|
Sudan
|
24
|
17
|
71%
|
|
|
2011
|
Uganda
|
Sudan
|
1
|
1
|
100%
|
|
|
2008
|
Democratic
Republic of Congo
|
Zaire
|
32
|
14
|
44%
|
|
|
2007
|
Uganda
|
Bundibugyo
|
149
|
37
|
25%
|
|
|
2007
|
Democratic
Republic of Congo
|
Zaire
|
264
|
187
|
71%
|
|
|
2005
|
Congo
|
Zaire
|
12
|
10
|
83%
|
|
|
2004
|
Sudan
|
Sudan
|
17
|
7
|
41%
|
|
|
2003
(Nov-Dec)
|
Congo
|
Zaire
|
35
|
29
|
83%
|
|
|
2003
(Jan-Apr)
|
Congo
|
Zaire
|
143
|
128
|
90%
|
|
|
2001-2002
|
Congo
|
Zaire
|
59
|
44
|
75%
|
|
|
2001-2002
|
Gabon
|
Zaire
|
65
|
53
|
82%
|
|
|
2000
|
Uganda
|
Sudan
|
425
|
224
|
53%
|
|
|
1996
|
South
Africa (ex-Gabon)
|
Zaire
|
1
|
1
|
100%
|
|
|
1996
(Jul-Dec)
|
Gabon
|
Zaire
|
60
|
45
|
75%
|
|
|
1996
(Jan-Apr)
|
Gabon
|
Zaire
|
31
|
21
|
68%
|
|
|
1995
|
Democratic
Republic of Congo
|
Zaire
|
315
|
254
|
81%
|
|
|
1994
|
Cote
d'Ivoire
|
Taï Forest
|
1
|
0
|
0%
|
|
|
1994
|
Gabon
|
Zaire
|
52
|
31
|
60%
|
|
|
1979
|
Sudan
|
Sudan
|
34
|
22
|
65%
|
|
|
1977
|
Democratic
Republic of Congo
|
Zaire
|
1
|
1
|
100%
|
|
|
1976
|
Sudan
|
Sudan
|
284
|
151
|
53%
|
|
|
1976
|
Democratic
Republic of Congo
|
Zaire
|
318
|
280
|
88%
|
Updated April 2014
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information contact:
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E-mail: mediainquiries@who.int
Telephone: +41 22 791 2222
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