What is Ebola Virus?
The Ebolavirus is a virus from the family of Filovirus. The species in this
genus are called ebolaviruses. Five species are known, and four of these
cause Ebola virus disease in humans, a type of hemorrhagic fever having
a very high case fatality rate. The five known virus spcies are
named after the region where each was originally identified. They include Bundibugyo ebolavirus, Reston
ebolavirus, Sudan
ebolavirus, Taï Forest ebolavirus (originally Côte d'Ivoire ebolavirus) and Zaire ebolavirus. The Zaire ebolavirus species is a sole
known member, which since 2010 has been called simply Ebola virus; this virus has the
highest mortality rate of the ebolaviruses and is also responsible for the
largest number of outbreaks of the five known members of the genus,
including both the first documented outbreak (1976) and the outbreak
with the most deaths (2014). The name Ebolavirus is derived from the Ebola River in Zaire (now
the Democratic Republic of the Congo), where Ebola virus was first discovered.
What is Ebola virus disease (EVD) or Ebola
hemorrhagic fever (EHF)
It is an infectious and generally fatal
disease marked by fever and severe internal bleeding, spread through contact
with infected body fluids by a filovirus ( Ebola virus ), whose normal host species is unknown.
Causes of the EVD
The EVD is generally caused
by four of five viruses classified in the genus Ebola virus, family Filoviridae,
order Mononegavirales. 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. Spreading through the
air has not been documented in the natural environment. Fruit bats are
believed to carry and spread the virus without being affected.
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.
Signs and Symptoms
Symptoms start two days to three weeks after contracting the
virus, with an influenzalike stage characterized by fever, fatique, muscle and abdominal pain and headaches. Less common symptoms include sore throat,
chest pain, hiccups, shortness of breath and trouble swallowing.
Typically, vomiting, diarrhea and rash follow, along
with decreased functioning of the
liver and kidneys. Around this time, affected
people may
begin to bleed both within the body and externally. 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 average time between
contracting the infection and the start of symptoms (incubation period) is 8 to
10 days, but it can vary between 2 and 21 days.
Skin manifestations may include a maculopapular rash (in
about 50% of cases). Early symptoms of EVD may be similar to those of malaria, dengue
fever or other tropical fevers, before the disease progresses to the
bleeding phase.
Diagnosis
To make the diagnosis, typically other diseases with similar
symptoms such as malaria, cholera, typhoid fever, shigellosis,
leptospirosis, plague, rickettsiosis, relapsing fever, meningitis, hepatitis and
other viral hemorrhagic fevers are first excluded. To confirm the
diagnosis, blood samples are tested for viral antibodies, viral RNA,
or the virus itself. This is achieved by
isolating the virus, detecting its RNA or proteins, or detecting antibodies against
the virus in a person's blood.
Isolating the virus by cell culture, detecting the viral
RNA by polymerase chain reaction (PCR) and detecting proteins by enzyme-linked
immunosorbent assay (ELISA) is effective early and in those who have died
from the disease. Detecting antibodies against the virus is effective late in
the disease and in those who recover.
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.
Prevention and Control
Ebola viruses are contagious,
with prevention predominantly involving behavior changes, proper full-body personal protective equipment, and disinfection. Techniques to avoid
infection involve not contacting infected blood or secretions, including from
those who are dead. This involves
suspecting and diagnosing the disease early and using standard precautions for all patients in the healthcare
setting. Recommended measures when caring for those who
are infected include isolating them, sterilizing equipment, and wearing
protective clothing including masks, gloves, gowns, and goggles. Hand washing is important but can be difficult in
areas where there is not even enough water for drinking. In an ongoing (2014) outbreak of Ebola in West
Africa, infection control items, even soap, are in short supply. When soap is difficult to obtain
during emergencies, the WHO promotes using substitutes such as clean ash (or
sand). The Ebola virus can be eliminated with heat (heating for 30 to 60
minutes at 60 °C or boiling for 5 minutes). On surfaces, some lipid
solvents such as some alcohol-based products, detergents, sodium hypochlorite
(bleach) or calcium hypochlorite (bleaching powder), and other suitable disinfectants
at appropriate concentrations can be used as disinfectants.
Due to lack of proper equipment and hygienic practices,
large-scale epidemics have occurred mostly in poor, isolated areas without modern
hospitals or well-educated medical staff. Traditional burial rituals, especially those requiring
washing or embalming of bodies, should be discouraged or
modified. Airline crews are instructed to isolate anyone
who has symptoms resembling Ebola virus.
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).
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.
Quarantine, also
known as enforced isolation, is usually effective in decreasing spread. Governments
often quarantine areas where the disease is occurring or individuals who may be
infected. In the United States, the law allows quarantine of those
infected with Ebola. The lack of roads and transportation may help
slow the disease in Africa. During the 2014 outbreak, Liberia closed schools.
Vaccine and Treatment
No vaccine is
currently available for humans. Several vaccines are being tested. They include DNA
vaccines or vaccines derived from adenoviruses, vesicular
stomatitis Indiana virus (VSIV) or filovirus-like particles
(VLPs) because these candidates could protect nonhuman primates from
ebolavirus-induced disease. DNA vaccines, adenovirus-based vaccines, and
VSIV-based vaccines have entered clinical trials. Recently there was a
breakthrough with Zmapp though it is still an experimental treatment.
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.
