EBOLA

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.
Table: Chronology of previous Ebola
virus disease outbreaks
Year Country Ebolavirus
species Cases
2012 Democratic
Republic of
Congo Bundibugyo 57
2012 Uganda Sudan 7
2012 Uganda Sudan 24
2011 Uganda Sudan 1
2008 Democratic
Republic of
Congo Zaire 32
2007 Uganda Bundibugyo 149
2007 Democratic
Republic of
Congo Zaire 264
2005 Congo Zaire 12
2004 Sudan Sudan 17
2003
(Nov-Dec)
Congo Zaire 35
2003 (Jan-
Apr)
Congo Zaire 143
2001-2002 Congo Zaire 59
2001-2002 Gabon Zaire 65
2000 Uganda Sudan 425
1996 South
Africa (ex-
Gabon) Zaire 1
1996 (Jul-
Dec)
Gabon Zaire 60
1996 (Jan-
Apr)
Gabon Zaire 31
1995 Democratic
Republic of
Congo Zaire 315
1994 Cote
d'Ivoire Taï Forest 1
1994 Gabon Zaire 52
1979 Sudan Sudan 34
1977 Democratic
Republic of
Congo Zaire 1
1976 Sudan Sudan 284
1976 Democratic
Republic of
Congo Zaire 318
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