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.
Favipiravir looks like
it may be useful in a mouse model of the disease. Estrogen receptor drugs used
to treat infertility and breast cancer (clomiphene and toremifene) inhibit the
progress of Ebola virus in infected mice. Ninety percent of the mice treated
with clomiphene and fifty percent of those treated with toremifene survived the
tests. Given their oral availability and history of human use, these drugs
would be candidates for treating Ebola virus infection in remote geographical
locations, either on their own or together with other antiviral drugs.
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.