Ebola Virus Disease

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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:
1. Bundibugyo ebolavirus (BDBV)
2. Zaire ebolavirus (EBOV)
3. Reston ebolavirus (RESTV)
4. Sudan ebolavirus (SUDV)
5. 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.

For more information contact:

WHO Media centre
Telephone: +41 22 791 2222
E-mail: mediainquiries@who.int

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