Biotechnology: Its Promises and Pathways

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BiotechnologyIts Promises and Pathways

• Spring 2006 Series

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• The Innovators
• Why Diseases EmergeThe World of Surveillance,
  Risk, and Response

Guy H. Palmer, DVM, Ph.D. Diplomate, American
College of Veterinary PathologistsProfessor of
Microbiology and PathologyCollege of Veterinary
Medicine
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Ro The Basic Reproductive Rateof Infection
Spread

• Three primary determinants of Ro
• Intrinsic ability to replicate and spread
• Infectious contacts
• Duration of infectiousness
• Ro gt1 Ongoing transmission
• Ro lt1 Self-limiting transmission

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Transmission of Measles Virus
Susceptible (uninfected)
Infectious (infected)
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Transmission of Measles Virus
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Effect of Small Population Sizeon Transmission
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Effect of Small Population Sizeon Transmission
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Effect of Large Population Sizeon Transmission
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Effect of Vaccination on Transmission
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Effect of Vaccination on Transmission
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Vaccination has DramaticNon-linear Effects on Ro
Threshold effects
Variation
Ro (Transmission risk)
50
100
of vaccinates in the population
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Effect of Population Structureon Transmission
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What causes major shifts ininfectious disease
patterns?

• Beneficial Development and deploymentof an
  effective vaccine
• Threshold for vaccine efficacy are unknownfor
  most major diseases
• Susceptible ?Infected ?Resistant
• Susceptible ?Infected (infectious) ?Infected
  (non-infectious)
• Detrimental Penetrance of a pathogeninto a
  susceptible population
• If highly virulent, leads to disease epidemic

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Emergence/Outbreak Reflectsan Increase in Ro

• Change in the intrinsic ability of a pathogento
  replicate and spread
• Genetic mutation or recombination
• Increase in infectious contacts
• Higher of susceptible individuals
• Increase in duration of infectiousness
• Pathogen or host level

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Evasion of Population Immunityis a Driving Force
in Emergenceof Infectious Disease
Susceptible (uninfected)
Infectious (infected)
Resistant (non-infected/immune)
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Study of Evasion of Population Immunity in
Real-time

• Anaplasma marginale isa tick-transmitted
  pathogen of livestock
• High rate of transmission in tropical countries
• Newborn calves are infected within the first6
  months
• Infection prevalencein a herd is 90-100

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Infected Animals are Resistantto Infection with
GeneticallySimilar Pathogen Strains

• Multiple closely related strains are presentand
  are transmitted within an animal population

A/F/A/F/I/F/F/H A/F/A/F/I/F/H A/F/A/F/H A/F/H
A/H
Strain diversity in a population of persistently
infected animals

• Individual animals carry only a single strain

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Detection of Strain Emergence
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St. M
D6E
B4
B5
B6
EM?
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1
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Emergence and spread of genetically distinct
strains
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35
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8
20
10
10
10
10
10
1
22
22
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55
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ES
ES
ES
ES
ES
ES
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Unanswered Questions

• How different does a new emergent strainneed to
  be?
• How frequent is pathogen emergence?
• How does population size affect frequencyand
  consequence of emergence?
• How does integrated control affect frequencyand
  consequence of emergence?
• What is the linkage between related traits(e.g.
  virulence) and emergence?

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How does understanding disease transmission
benefit society?

• Clearly understood models can effectivelydrive
  public health and animal health policy
• Uncertainty has a real cost
• Threshold effects show that integrated
  control(e.g. vector control and vaccination) may
  have disproportionate and unpredicted impact
• Population size has direct relevance to
  bothdisease risk and vaccine implementation
• Small-holder farms in sub-Saharan
  Africa,South-east Asia, and Central and South
  America

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Vector-borne Pathogens are theMajor Cause of
Livestock Disease in Tropical Lesser Developed
Countries

• The mean cattle herd size in Africa ranges from
  3.2-5.9 animals
• Is a primary determinant of household economic
  security
• Vaccine development targeted to the small-holder
  population

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Initiative to Develop Sustainable Vaccine Control
in Central and South America

• WSU is the lead institution in the U.S.
• Field based research in Mexico and Argentina
• Role of WSU alumni
• Extension to Central America and Andean countries

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Washington State University U.S. National
Institutes of Health The Wellcome Trust
Initiative in AnimalHealth in the Developing
World
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• Coming Soon
• Fall 2006 Innovators Series
• www.wsu.edu/theinnovators
• Toll free 1-877-978-3868

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