Smallpox, a potential problem

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Smallpox, a potential problem

• Julia Higgins
• MSc Molecular Medical Microbiology

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Contents

• Introduction and History
• Epidemiology and Transmission
• Microbiology and Pathogenesis
• Clinical Features
• Methods to counteract pre-exposure and
  post-exposure
• Potential as a Bioterrorist Weapon
• Conclusion

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Introduction and History

• Introduction
• Smallpox (Variola) feared most devastating of all
  infectious diseases
• WHO declared smallpox extinct 1980
• Consequently no further need for immunisation
  programs

• History
• Smallpox illness of humans 3,000 years
• Edward Jenner, father of smallpox vaccination
  1798
• Smallpox largely eradicated early 20th Century

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Epidemiology Transmission

• Only officially exists in two laboratories in
  World CDC Atlanta USA Koltsovo former USSR
• Transmission mainly via airborne route
• Only person to person, no animal reservoir or
  insect vector
• Can be via direct contact of vesicle fluid,
  saliva and respiratory secretions
• Contaminated linen and clothing

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Microbiology Pathogenesis

• Microbiology
• Member of genus Orthopoxvirus
• Double-stranded DNA virus
• Virion brick-shaped structure 200nm diameter
• Uses host enzymes for replication

• Pathogenesis
• Infective dose believed to be only few virions
• Migration multiplication in lymph nodes
• Asymptomatic viremia
• 20 viremia followed by fever

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Clinical Features

• Incubation period 12 days
• Flu-like symptoms
• Lesions to macules to papules to vesicles to
  pustules
• Scabbing of pustules

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Table 1 Comparison in onset, symptoms and rates
of fatality in variations of Smallpox
Infections  
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Smallpox lesions on skin of trunk. Picture taken
in Bangladesh, 1973. Public Health Images Library
(PHIL) ID 284. Source CDC/James Hicks
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• A Practical treatise on smallpox
  illustrated by coloured photographs from life /
  by George Henry Fox with the collaboration of
  S.D. Hubbard, S. Pollitzer, and J.H. Huddleston.
  Philadelphia Lippincott, c1902

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Figure 1. Typical Temperature Chart of Patient
With Smallpox Infection
Chart adapted from JAMA June 9th 1999
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Measures to counteract pre-exposure and
post-exposure

• Pre-exposure
• Natural immunity from previous exposure to virus
• Routine vaccination Completely stopped in 1979
  as recommended by WHO.
• Vaccination only effective for 10 years
• Previous vaccination reduces effects of virus

• Post-exposure
• Vaccine up to 4 days after exposure to virus
• No Antiviral therapy except treatment of symptoms
• Compounds cidofovir and adefovir
• Cidofovir evidence of promising results

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Potential as a Bioterrorist Weapon

• Widespread immunity no longer in population
• Increase in immune disorders results in increased
  fatality
• Only 90 million vaccines readily available
  worldwide (15.4 million USA alone)
• Rate of transmission estimated at 10-20 new
  infections per infected person
• Reports from Ken Alibek of successful programs to
  produce smallpox in large quantities

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Conclusion

• Worldwide need to produce sufficient supply of
  vaccines to combat potential deliberate release
• Worldwide need to mass produce bifurcated needle
  to administer vaccines
• Merck Company to mass produce vaccines for USA
• Research to develop antiviral drugs to treat
  virus
• Because of the lack of immunity all the above
  need to be addressed post haste in the event of
  an intentional release
• As it stands the release of smallpox would pose a
  potential danger