Key facts
·
Ebola virus disease (EVD), formerly known as Ebola haemorrhagic
fever, is a severe, often fatal illness in humans.
·
The virus is transmitted to people from wild animals and spreads
in the human population through human-to-human transmission.
·
The average EVD case fatality rate is around 50%. Case fatality
rates have varied from 25% to 90% in past outbreaks.
·
The first EVD outbreaks occurred in remote villages in Central
Africa, near tropical rainforests, but the most recent outbreak in west Africa
has involved major urban as well as rural areas.
·
Community engagement is key to successfully controlling
outbreaks. Good outbreak control relies on applying a package of interventions,
namely case management, surveillance and contact tracing, a good laboratory
service, safe burials and social mobilisation.
·
Early supportive care with rehydration, symptomatic treatment
improves survival. There is as yet no licensed treatment proven to neutralise
the virus but a range of blood, immunological and drug therapies are under
development.
·
There are currently no licensed Ebola vaccines but 2 potential
candidates are undergoing evaluation.
Background
The Ebola virus causes an acute, serious illness which is often
fatal if untreated. Ebola virus disease (EVD) first appeared in 1976 in 2
simultaneous outbreaks, one in Nzara, Sudan, and the other in Yambuku,
Democratic Republic of Congo. The latter occurred in a village near the Ebola
River, from which the disease takes its name.
The current outbreak in west Africa, (first cases notified in
March 2014), is the largest and most complex Ebola outbreak since the Ebola
virus was first discovered in 1976. There have been more cases and deaths in
this outbreak than all others combined. It has also spread between countries
starting in Guinea then spreading across land borders to Sierra Leone and
Liberia, by air (1 traveller only) to Nigeria, and by land (1 traveller) to
Senegal.
The most severely affected countries, Guinea, Sierra Leone and
Liberia have very weak health systems, lacking human and infrastructural
resources, having only recently emerged from long periods of conflict and
instability. On August 8, the WHO Director-General declared this outbreak a
Public Health Emergency of International Concern.
A separate, unrelated Ebola outbreak began in Boende, Equateur, an
isolated part of the Democratic Republic of Congo.
The virus family Filoviridae includes 3 genera: Cuevavirus,
Marburgvirus, and Ebolavirus. There are 5 species that have been identified:
Zaire, Bundibugyo, Sudan, Reston and Taï Forest. The first 3, Bundibugyo
ebolavirus, Zaire ebolavirus, and Sudan ebolavirus have been associated with
large outbreaks in Africa. The virus causing the 2014 west African outbreak
belongs to the Zaire species.
Transmission
It is thought that fruit bats of the Pteropodidae family are
natural Ebola virus hosts. Ebola is introduced into the human population
through close contact with the blood, secretions, organs or other bodily fluids
of infected animals such as chimpanzees, gorillas, fruit bats, monkeys, forest
antelope and porcupines found ill or dead or in the rainforest.
Ebola then spreads through human-to-human transmission via direct
contact (through broken skin or mucous membranes) with the blood, secretions,
organs or other bodily fluids of infected people, and with surfaces and
materials (e.g. bedding, clothing) contaminated with these fluids.
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.
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.
People remain infectious as long as their blood and body fluids,
including semen and breast milk, contain the virus. Men who have recovered from
the disease can still transmit the virus through their semen for up to 7 weeks
after recovery from illness.
Symptoms of Ebola
virus disease
The incubation period, that is, the time interval from infection
with the virus to onset of symptoms is 2 to 21 days. Humans are not infectious
until they develop symptoms. First symptoms are the sudden onset of fever
fatigue, muscle pain, headache and sore throat. This is followed by vomiting,
diarrhoea, rash, symptoms of impaired kidney and liver function, and in some
cases, both internal and external bleeding (e.g. oozing from the gums, blood in
the stools). Laboratory findings include low white blood cell and platelet
counts and elevated liver enzymes.
Diagnosis
It can be difficult to distinguish EVD from other infectious
diseases such as malaria, typhoid fever and meningitis. Confirmation that
symptoms are caused by Ebola virus infection are made using the following
investigations:
·
antibody-capture enzyme-linked immunosorbent assay (ELISA)
·
antigen-capture 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; laboratory
testing on non-inactivated samples should be conducted under maximum biological
containment conditions.
Treatment and vaccines
Supportive care-rehydration with oral or intravenous fluids- and
treatment of specific symptoms, improves survival. There is as yet no proven
treatment available for EVD. However, a range of potential treatments including
blood products, immune therapies and drug therapies are currently being
evaluated. No licensed vaccines are available yet, but 2 potential vaccines are
undergoing human safety testing.
Prevention and control
Good outbreak control relies on applying a package of
interventions, namely case management, surveillance and contact tracing, a good
laboratory service, safe burials and social mobilisation. Community engagement
is key to successfully controlling outbreaks. Raising awareness of risk factors
for Ebola infection and protective measures that individuals can take is an
effective way to reduce human transmission. Risk reduction messaging 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 from
direct or close contact with people with Ebola symptoms, particularly with
their bodily fluids. 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.
·
Outbreak containment measures including
prompt and safe burial of the dead, identifying people who may have been in
contact with someone infected with Ebola, monitoring the health of contacts for
21 days, the importance of separating the healthy from the sick to prevent
further spread, the importance of good hygiene and maintaining a clean
environment.
Controlling infection
in health-care settings:
Health-care workers should always take standard precautions when
caring for patients, regardless of their presumed diagnosis. These include
basic hand hygiene, respiratory hygiene, use of personal protective equipment
(to block 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 extra infection control measures to prevent
contact with the patient’s blood and body fluids and contaminated surfaces or
materials such as clothing and bedding. 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 humans and
animals for investigation of Ebola infection should be handled by trained staff
and processed in suitably equipped laboratories.
WHO response
WHO aims to prevent Ebola outbreaks by maintaining surveillance
for Ebola virus disease and supporting at-risk countries to developed
preparedness plans. The document provides overall guidance for control of Ebola
and Marburg virus outbreaks:
When an outbreak is detected WHO responds by supporting
surveillance, community engagement, case management, laboratory services,
contact tracing, infection control, logistical support and training and
assistance with safe burial practices.
WHO has developed detailed advice on Ebola infection prevention
and control:
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
Telephone: +41 22 791 2222
E-mail: mediainquiries@who.int
