Part 3 SARS CoV

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Part 3SARS Co-V
Coronavirus Life Cycle
Coronavirus
2
Genome Sequence

• Genome sequence data of SARS Co-V reveal that
  novel agent does not belong to any of the known
  groups of coronaviruses, including two human
  coronaviruses, HCoV-OC43 and HCoV-229E.
• SARS-CoV genome appears to be equidistant from
  those of all known coronaviruses.

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Genome Sequence (cont.)

• Closest relatives are the murine, bovine,
  porcine, and human coronaviruses in group 2 and
  avian coronavirus IBV in group 1
• Genome shows SARS-CoV is neither a mutant of a
  known coronavirus, nor a recombinant between
  known coronaviruses.

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SARS-CoV maintaining consensus genotype

• SARS-CoV seems well-adapted to the human host.
• Genetic analysis is able to distinguish between
  different strains of SARS-CoV.
• Great value for epidemiological studies and for
  clinical implications

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Morphology

• Negative-stain transmission electron microscopy
  of patient samples and of cell culture
  supernatants reveals pleomorphic, enveloped
  coronavirus-like particles with diameters of
  between 60 and 130 nm.
• Extra cellular particles accumulate in large
  clusters frequently seen lining the surface of
  the plasma membrane.
• Source MMWR 2003 52 241-248

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Organization

• SARS-CoV genome contains five major ORFs
• Replicase polyprotein
• The spike (S)
• Envelope (E)
• Membrane (M) glycoproteins
• Nucleocapsid protein (N)

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S Protein

• Bind to species-specific host cell receptors and
  to trigger a fusion event between viral envelope
  and a cellular membrane
• Shown to be a virulence factor in many different
  coronaviruses
• Principal viral antigen that elicits neutralizing
  antibody on behalf of host

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M Protein

• Major component of the virion envelope
• Major determinant of virion morphogenesis,
  selecting S protein for incorporation into
  virions
• M protein also selects the genome for
  incorporation into the virion.

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High Rate of RNA-RNA Recombination
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SARS Co-V Detected in Multiple Specimens

• Extract of lung and kidney tissue by virus
  isolation or PCR
• Bronchoalveolar lavage specimens by virus
  isolation, electron microscopy and PCR
• Sputum or upper respiratory tract swab, aspirate,
  or wash specimens by PCR

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Co-V RNA Detection

• High concentrations of viral RNA found in sputum
• RT-PCR in 32 at initial presentation and in 68
  at day 14
• In stool samples, detected in 97 of patients two
  weeks after illness
• 42 urine positive for viral RNA
• Viral RNA detected at extremely low
  concentrations in plasma

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Stability and Resistance

• Work is on-going to evaluate stability of
  SARS-CoV and its resistance against environmental
  factors and disinfectants.
• Virus is stable in feces and urine at room
  temperature for 1-2 days.
• Stability seems to be higher in stools from
  patients with diarrhea.

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Reduction in Concentration of virus

• In supernatants of infected cell cultures,
  minimal reduction in concentration of virus after
  21 days at 4C and -80C
• After 48 hours at room temperature, concentration
  of virus reduced by one log only, virus more
  stable

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Natural Host

• Researcher found the virus in masked palm civets
  and some other species.
• Civets found to harbor SARS coronavirus detected
  by a PCR.
• Serum from animals inhibited growth of SARS-CoV
  isolated from humans.
• Vice versa, human serum from SARS patients
  inhibited growth of SARS isolates from animals.

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Antiviral Drugs

• Antiviral Drugs Efforts are underway to assess
  potential anti-SARS-CoV agents in vitro.
• Ribavirin, a "broad spectrum" agent, seems to
  lack in vitro efficacy.
• Convalescent plasma and normal human
  immunoglobulin, have also been used in SARS
  patients.

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Vaccines

• Relative ease with which SARS-CoV can be
  propagated in vitro and the availability of
  vaccines against animal coronaviruses avian
  infectious bronchitis virus, transmissible
  gastroenteritis coronavirus of pigs, feline
  infectious peritonitis virus are encouraging.
• S protein is a good target for vaccines it will
  elicit neutralizing antibody.

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Vaccines (Cont.)

• Apparent genetic stability of SARS-CoV is
  encouraging with regard to the development of a
  vaccine.
• Before immunization strategies are devised, the
  immune pathogenesis of feline infectious
  peritonitis warrants careful investigation into
  whether immune enhancement also plays a role in
  SARS.

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Rapid Success Approach

• Discovery of coronavirus result of global
  collaborative exercise by WHO
• High-level laboratory investigators
• Making use of all available techniques cell
  culture through electron microscopy
• Address the threat of emerging infectious
  diseases in the 21st century

Sources World Health Organization Multicentre
Collaborative Network for Severe Acute
Respiratory Syndrome (SARS) Diagnosis
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Further out-breaks

• Unclear whether SARS will reappear or not
• Clinically "silent" infections and long-term
  carriage can not be ruled out Further out-breaks
  season-dependent manner.
• Coronavirus persists in an unidentified animal
  reservoir may again spill over into the human
  population.
• Vigilance for new SARS cases be maintained.

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Sustained control of SARS required

• Reliable diagnostic tests development
• Effective vaccine development is a realistic
  possibility.
• Suitable animal models must demonstrate efficacy.
• Time is necessary to demonstrate safety of new
  vaccine in humans.
• Involvement by commercial enterprises is clearly
  wanted and necessary.

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Electron micrograph of corona virus-like
particles in cell culture
Source Department of Virology, Bernhard Nocht
Institute for Tropical Medicine Director H.
Schmitz full-size picture
22
Cytopathic effect in Vero cell culture
Source Institute
for Medical Virology, Director H. W. Doerr
full-size picture
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Phylogenetic Tree of SARS-CoV
Source S. Günther, Department of Virology,
Bernhard Nocht Institute for Tropical Medicine
Director H. Schmitz full-size picture