Ebola virus disease
Fact sheet N°103
Updated April 2014
from World Health Organization Web page
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
