Ebola virus disease (EVD), earlier
known as Ebola hemorrhagic fever, is a severe, often causes fatal illness in
humans. The virus is transmitted to people from wild animals and spreads in the
human population through human-to-human transmission. The average EVD case
fatality rate is around 50%. Case fatality rates have varied from 25% to 90% in
past outbreaks. The first EVD outbreaks occurred in distant villages in Central
Africa, near humid rainforests, but the most recent outbreak in West Africa has
involved major urban as well as rural areas.
Community engagement is key to successfully
controlling outbreaks. Good outbreak control relies on applying a package of
interventions, namely case management, surveillance and contact tracing, a good
laboratory service, safe burials and social mobilization. Early supportive care
with rehydration, symptomatic treatment improves survival. There is as yet no
licensed treatment proven to neutralize the virus but a range of blood,
immunological and drug therapies are under development. There are currently no
licensed Ebola vaccines but 2 potential candidates are undergoing evaluation.
History
of EVD
The Ebola virus causes severe,
serious illness which is often fatal if untreated. Ebola virus disease (EVD)
first appeared in 1976 in 2 simultaneous outbreaks, one in Nzara, Sudan, and
the other in Yambuku, Democratic Republic of Congo. The later occurred in a
village near the Ebola River, from which the disease takes its name.
The current outbreak in West Africa,
(first cases notified in March 2014), is the largest and most complex Ebola
outbreak since the Ebola virus was first discovered in 1976. There have been
more cases and deaths in this outbreak than all others combined. It has also
spread between countries starting in Guinea then spreading across land borders
to Sierra Leone and Liberia, by air (1 traveller only) to Nigeria, and by land
(1 traveller) to Senegal.
The most severely affected
countries, Guinea, Sierra Leone and Liberia have very weak health systems,
lacking human and infrastructural resources, having only recently emerged from
long periods of conflict and instability. On August 8, the WHO Director-General
declared this outbreak a Public Health Emergency of International Concern.
A separate, unrelated Ebola outbreak
began in Boende, Equateur, an isolated part of the Democratic Republic of
Congo.
The virus family Filoviridae
includes 3 genera: Cuevavirus, Marburgvirus, and Ebolavirus. There are 5
species that have been identified: Zaire, Bundibugyo, Sudan, Reston and Taï
Forest. The first 3, Bundibugyo ebolavirus, Zaire ebolavirus, and Sudan
ebolavirus have been associated with large outbreaks in Africa. The virus
causing the 2014 West African outbreak belongs to the Zaire species.
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Transmission
It is thought that fruit bats of the
Pteropodidae family are natural Ebola virus hosts. Ebola is introduced into the
human population through close contact with the blood, secretions, organs or
other bodily fluids of infected animals such as chimpanzees, gorillas, fruit
bats, monkeys, forest antelope and porcupines found ill or dead or in the
rainforest.
Ebola then spreads through
human-to-human transmission via direct contact (through broken skin or mucous
membranes) with the blood, secretions, organs or other bodily fluids of
infected people, and with surfaces and materials (e.g. bedding, clothing) polluted
with these fluids.
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.
Burial ceremonies in which widows
have direct contact with the body of the deceased person can also play a role
in the transmission of Ebola.
People remain infectious as long as
their blood and body fluids, including sperm and breast milk, contain the
virus. Men who have recovered from the disease can still transmit the virus
through their sperm for up to 7 weeks after recovery from illness.
Symptoms
of Ebola virus disease
The development period, that is, the
time interval from infection with the virus to onset of symptoms is 2 to 21
days. Humans are not infectious until they develop symptoms. First symptoms are
the sudden onset of fever fatigue, muscle pain, headache and sore throat. This
is followed by vomiting, diarrhea, rash, symptoms of weakened kidney and liver
function, and in some cases, both internal and external bleeding (e.g. emission
from the secretions, blood in the stools). Laboratory findings include low
white blood cell and platelet counts and elevated liver enzymes.
Diagnosis
It can be difficult to distinguish
EVD from other infectious diseases such as malaria, typhoid fever and
meningitis. Confirmation that symptoms are caused by Ebola virus infection are
made using the following investigations:
- antibody-capture enzyme-linked immunosorbent assay (ELISA)
- antigen-capture 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; laboratory testing on non-inactivated samples should be
conducted under maximum biological containment conditions.
Treatment
and vaccines
Supportive care-rehydration with
oral or intravenous fluids- and treatment of specific symptoms, improves
survival. There is as yet no proven treatment available for EVD. However, a
range of potential treatments including blood products, immune therapies and
drug therapies are currently being evaluated. No licensed vaccines are
available yet, but 2 potential vaccines are undergoing human safety testing.
Prevention
and control
Good outbreak control relies on
applying a package of interventions, namely case management, surveillance and
contact tracing, a good laboratory service, safe burials and social
mobilisation. Community engagement is key to successfully controlling
outbreaks. Raising awareness of risk factors for Ebola infection and protective
measures that individuals can take is an effective way to reduce human
transmission. Risk reduction messaging 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 from direct or close contact with people with Ebola symptoms, particularly with their bodily fluids. 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.
- Outbreak containment measures including prompt and safe burial of the dead, identifying people who may have been in contact with someone infected with Ebola, monitoring the health of contacts for 21 days, the importance of separating the healthy from the sick to prevent further spread, the importance of good hygiene and maintaining a clean environment.
Controlling
infection in health-care settings:
Health-care workers should always
take standard precautions when caring for patients, regardless of their
presumed diagnosis. These include basic hand hygiene, respiratory hygiene, use
of personal protective equipment (to block 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 extra infection
control measures to prevent contact with the patient’s blood and body fluids
and contaminated surfaces or materials such as clothing and bedding. 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 humans and animals for investigation of Ebola infection
should be handled by trained staff and processed in suitably equipped
laboratories.