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 |
|
