Ebola virus disease
Fact sheet N°103
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.
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.
Source :-http://www.who.int/mediacentre/factsheets/fs103/en/
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