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.
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 clinicallyasymptomatic.
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: WHO Website
url: http://www.who.int/mediacentre/factsheets/fs103/en/
