Page 341 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART IV Clinical Virology
330
polymerase in the virion. The nucleocapsid has helical
occurred in Liberia, Sierra Leone, and Guinea in which
symmetry. The surface proteins of Ebola virus are antigeni-
cally distinct from those of Marburg virus.
more than 10,000 people died. The fatality rate is 60% in
Ebola virus is one of the most virulent human viruses
this epidemic. This epidemic included cases in both rural
and is cultured only under the highest biosafety contain-
and highly populated areas.
ment (BSL-4). It can be inactivated by lipid solvents and
bleach (hypochlorite).
There are five types: Ebola-Zaire is the most pathogenic
The high mortality rate of Ebola virus is attributed to sev-
for humans and Ebola-Reston is pathogenic for monkeys Pathogenesis & Immunity
eral viral virulence factors: Its glycoprotein kills endothelial
but not for humans. Ebola-Sudan is also highly pathogenic.
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cells, resulting in hemorrhage, and two other proteins
The degree of pathogenicity of Ebola-Ivory Coast (Tai For-
inhibit the induction and action of interferon. Lympho-
est) and Ebola-Bundibugyo for humans is uncertain
because the number of cases is relatively small. The Zaire,
result, the antibody response is often ineffective in prevent-
Sudan, Ivory Coast, and Bundibugyo types are found in
ing disease. Hepatocytes are also killed leading to liver
Africa whereas the Reston type originated in the
failure.
Philippines.
Clinical Findings
Summary of Replicative Cycle
The general outline of its replication is similar to that of
to 21 days. EHF begins with a constellation of symptoms
other negative-stranded RNA enveloped viruses. After the
some of which are fever, headache, sore throat, myalgia,
virion envelope glycoproteins bind to the surface of the The incubation period is typically 5 to 7 days but may be up
arthralgia, epigastric pain, vomiting, and diarrhea. Later,
human cell, the nucleocapsid enters the cytoplasm where
bleeding into the skin and gastrointestinal tract occurs, fol-
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the virion RNA polymerase transcribes the seven genes
lowed by shock and disseminated intravascular coagulation
into individual messenger RNAs. The m-RNAs are trans-
leading to multiorgan failure. The hemorrhages are the
lated into structural and nonstructural proteins. The
negative-strand progeny genome is synthesized by the
thelial cells. Marked lymphopenia occurs. The mortality
virus-encoded RNA polymerase using a plus-strand tem-
rate associated with this virus can be up to 90%.
plate. The newly synthesized nucleocapsid proteins sur-
In some patients who recover from EHF, a post-Ebola
round both the progeny genome and the virion RNA
syndrome (PES) occurs. The findings in PES include eye
polymerase. The matrix protein then mediates the inter-
pain, blurred vision, hearing loss, headache, joint pain,
action of the nucleocapsid protein with the outer cell
fatigue, and insomnia. In one patient with uveitis, infec-
membrane at the site of the progeny envelope proteins.
tious Ebola virus was recovered from fluid aspirated from
The progeny virus then buds from the surface of the
the interior of his eye several months after recovery.
infected cell.
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Transmission & Epidemiology
Diagnosis is most often made by detecting viral antigens in
serum using an ELISA assay, by detecting viral RNA using
The natural reservoir of Ebola virus is unknown. Fruit bats
a PCR assay, or by detecting IgM antibody in the serum.
or rodents are suspected of being the reservoir. Monkeys
(Extreme care must be taken when handling specimens in
can be infected but, because they become sick and die, are
the laboratory.) The virus can be cultured in monkey cells
unlikely to be the natural reservoir. The mode of transmis-
in BSL-4 containment facility. Electron microscopy may
sion from the reservoir host to humans is unknown.
reveal the long rod-shape of a filovirus, implicating either
Transmission from human to human occurs via blood
Ebola virus or Marburg virus.
and body fluids. Hospital personnel without adequate pro-
tection are especially at risk. Many cases arise by secondary
transmission from contact with the patient’s blood or secre-
No antiviral therapy is available. Supportive therapy includ-
tions (e.g., in hospital staff). Reuse of needles and syringes
has been implicated in the spread in some hospitals in Treatment & Prevention
ing intravenous fluids and electrolytes is useful. Treatment
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resource-poor countries. There is no evidence for human
with immune serum globulins containing antibody to
Ebola virus has had variable results. An experimental
disease occurring via airborne transmission or by casual
personal contact. There is evidence of Ebola virus persist-
monoclonal antibody (ZMapp) was used in the 2014 epi-
ing in the semen of survivors of the disease.
Subsequent to the first recorded outbreak of EHF in
Prevention centers on limiting secondary spread by
1976, there have been sporadic outbreaks in rural areas in
proper handling of patient’s secretions and blood and by
the wearing of personal protective equipment (PPE).
various sub-Saharan African countries, mostly in the 1990s
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