EBOLA VIRUS

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.

Source: W.H.O