Source :WHO
Ebola
virus disease
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%
|
Source : WHO http://www.who.int/mediacentre/factsheets/fs103/en/