PART V: Discussion

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PART V Discussion
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Factors leading to the emergence of infectious
diseases
Changes in society, technology, environment and
microorganisms are leading to increases in host
susceptibility and/or disease transmission and
the evolution of new or drug-resistant
microorganisms
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Candidate Factors AffectingEmergence of SARS

• Human demographics and behavior
• Human susceptibility to infection
• Economic development and land use
• Changing ecosystems
• International travel and commerce
• Microbial adaptation and change
• Breakdown of public health measures
• To be determined . . .

IOM Microbial Threats to Health Emergence,
Detection, and Response. March 2003.
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Infectivity

• Infectivity is the ability of a virus to jump
  from one person to another
• The recipient must receive a dose large enough to
  cause the disease
• From epidemic reports, it appears that SARS virus
  has low infectivity (ie it requires a large dose
  to pass on to the recipient)
• Other members of the coronavirus family have very
  high infectivity.

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Virulence

• Virulence is the property of the virus to cause
  damage to the patients organs
• The SARS virus is very virulent
• Other members of the coronavirus family have low
  virulence.

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Attenuation

• Attenuation is a phenomenon seen in some members
  of the coronavirus family, where the virulence
  decreases when it jumps from person to person.
• Initial decrease in cases suggested attenuation
• Enough information is still not available to
  suggest this phenomenon in the current SARS
  outbreak
• Recent clusters suggest that the virus might be
  getting more virulent

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Seasonal incidence of coronavirus infections
Disease is now in the Spring season?
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Research in China

• Organ samples of 7 fatal cases of SARS
• 293 cell line inoculated from materials derived
  from lung to isolated the agent(s)
• Agents in organs and cell cultures revealed by
  immunoassay
• Result
• Chlamydia-like Coronavirus-like particles found
  on EM
• Chlamydia-like agent visualized in both organs
  and cells
• Were non-reactive with
• genus-specific antibodies against Chlamydia
• monoclonal antibodies against chlamydia
  pneumoniae and c. psittaci
• Results consistent with a novel chlamydia-like
  agent

Source Hong T. et al. Chlamydia-like and
coronavirus-like agents found in dead cases of
atypical pneumonia by electron microscopy.
National Medical Journal China 200383632-6
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Addressing the Threat of SARS

• Enhancing global response capacity
• Improving global infectious disease surveillance
• Rebuilding domestic public health capacity
• Developing diagnostics
• Educating and training multidisciplinary
  workforce
• Vaccine development and production
• Need for new antimicrobial drugs

IOM Microbial Threats to Health Emergence,
Detection, and Response. March 2003.
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Unanswered Questions?

• Future course of outbreak
• Source of virus
• Mode of transmission in community
• Risk of household transmission
• Risk of transmission on airplanes and ships
• Environmental persistence/decontamination

• Period of infectiousness
• Explanation for age distribution
• Importance of hypertransmitters
• Role of co-infection
• Optimal diagnostic test(s)
• Effective therapy
• Vaccine approaches

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Thank you!!!!!!