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.
WHO response
WHO provides expertise and documentation to support disease
investigation and control.
Recommendations for infection control while providing care
to patients with suspected or confirmed Ebola haemorrhagic fever are provided
in: Interim infection control recommendations for care of patients with
suspected or confirmed Filovirus (Ebola, Marburg) haemorrhagic fever, March
2008. This document is currently being updated.
WHO has created an aide–memoire on standard precautions in
health care (currently being updated). Standard precautions are meant to reduce
the risk of transmission of bloodborne and other pathogens. If universally
applied, the precautions would help prevent most transmission through exposure
to blood and body fluids.
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%
|
|
For more information contact:
WHO Media centre
Telephone: +41 22 791 2222
E-mail: mediainquiries@who.int
