Ebola
virus disease outbreaks can devastate families and communities, but the
infection can be controlled through the use of recommended protective
measures in clinics and hospitals, at community gatherings, or at home.
In Brief
- 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.
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.
Source: WHO
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