Epidemiology

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Epidemiology

• Study of Disease Occurrence and Transmission

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Emerging Infectious Disease

• Mutation of organism to new serovar (antigenic
  type)
• Migration of humans and animals into new
  environments
• Travel
• War and natural disasters
• Decline in vaccination rates
• Climatic changes

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Microbe of the Day

• Vibrio cholerae
• Gram negative curved rod
• Toxin alters sodium pump in intestinal cells ?
  fluid loss

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Cholera 1800s
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Cholera the Disease

• Entry oral
• Colonization small intestine
• Symptoms nausea, diarrhea, muscle cramps, shock

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Infant with Cholera
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First Cholera Pandemic

• Why does an epidemic end?

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Second Cholera Pandemic
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Cholera New York 1830s
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John Snow and the Pump Handle

• John Snow and cholera in 1854 London
  http//www.ph.ucla.edu/epi/snow.html

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John Snow

• John Snow is credited by many with developing the
  modern field of epidemiology

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London in the 1850s

• Germ theory of disease not widely accepted
• People lived in very crowded conditions with
  water and privies in yard (NY 1864 900 people in
  2 buildings 180 deep x 5 stories 1 pump a
  block away, privy in yard)

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Water Supply London 1850s
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John Snows Observations

• People with cholera developed immediate digestive
  problems cramps, vomiting, diarrhea
• Face, feet, hands shriveled and turned blue died
  in less than a day
• Probably spread by vomiting and diarrhea

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Cholera Epidemiology

• Comparison of pump location with cholera deaths,
  first 3 days of epidemic in 1854

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Cholera Epidemiology

• Of 83 people, only 10 lived closer to a different
  pump than Broad Street
• Of these 10, 5 preferred taste of Broad Street
  water and 3 were children who went to nearby
  school

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Cholera Epidemiology

• Snow convinced neighborhood council to let him
  remove handle from water pump on Broad Street -
  new cases declined dramatically
• Many on council not convinced by his evidence

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Snow Index Case
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Snow Index Case

• Index case is first person to become ill
• 40 Broad Street husband and infant child became
  ill
• Wife soaked diapers in pail and emptied pail into
  cistern next to pump

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The Great Experiment

• Two water companies supplied central London
• Customers mixed in same neighborhood
• Snow went door to door asking which water company
  served home and compared locations with cholera
  data

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The Great Experiment

• Lambeth Company water intake upstream of London
  sewage outfall into Thames
• Southwark Vauxhall Company water intake
  downstream of sewage outfall

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The Great Experiment
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Cholera in the 1990s

• Epidemic in Peru beginning 1991
• From 1991-1994
• Cases 1,041,422
• Deaths 9,642 (0.9)
• Originated at coast, spread inland

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World Cholera 2000-01
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Why Has Cholera Re-emerged?

• Deteriorating sanitary facilities as larger
  population moves into shanty towns
• Trujullo, Peru fear of cancer from chlorination
  so water untreated
• Use of wastewater on crops
• Africa civil wars and drought caused migrations
  into camps

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How Has Cholera Re-emerged?

• Simultaneous appearance along whole coast of
  Peru
• Traveled in ship ballast?
• Traveled in plankton from Asia?
• Always present in local zooplankton (copepods)
  but dormant until triggered by ???

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Copepod Carrying Vibrio cholerae
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Cholera and El Niño

• Periodic warming of water near coast of Central
  and South America
• Large plankton blooms, especially in coastal
  waters with nutrients from sewage runoff

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Cholera and El Niño

• Cholera in Bangladesh also seen to fluctuate with
  El Niño, but with 11 month lag
• Rita Colwell and multinational group studying
  link between climate and cholera
• Satellite and surface data used to show cholera
  incidence is related to sea surface temperature

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Cholera from Space
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Cholera and Sea Surface Temperature
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Cholera in the 1990s

• Cholera O139 emerges in Asia
• Different O (coat) antigen, 99 genetic identity
• O antigen is how human immune system recognizes
  and protects against V. cholerae
• More people susceptible

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Cholera Antibiotic Resistance

• Cholera is becoming resistant to several
  antibiotics