Evolution of Virulence

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Evolution of Virulence Matthew H. Bonds The
François-Xavier Bagnoud Center for Health and
Human Rights Harvard School of Public
Health Partners in Health
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Outline of Presentation

• Background to Disease Evolution
• - Evolution of virulence
• - Antibiotic resistance
• - Disease emergence
• Evolutionary Stable Strategies (ESS)
• Evolution of Virulence
• - single infection
• - multiple infections

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Background to Disease Evolution

1. Evolution of Virulence
2. Antibiotic Resistance
3. Disease Emergence

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Background to Disease Evolution

1. Evolution of Virulence
2. Antibiotic Resistance
3. Disease Emergence

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Background to Disease Evolution

• Evolution
• A change in genetic material in a population
  from generation to the next.
• - We say that organisms evolve to maximize
  their fitness

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Background to Disease Evolution

• Evolution
• A change in genetic material in a population
  from generation to the next.
• - We say that organisms evolve to maximize
  their fitness
• 2. Fitness ? Reproductivity

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Background to Disease Evolution

• Evolution
• A change in genetic material in a population
  from generation to the next.
• - We say that organisms evolve to maximize
  their fitness
• 2. Fitness ? Reproductivity number of
  surviving offspring or number of reproductive
  offspring

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Background to Disease Evolution

• Evolution
• A change in genetic material in a population
  from generation to the next.
• - We say that organisms evolve to maximize
  their fitness
• 2. Fitness ? Reproductivity number of
  surviving offspring or number of reproductive
  offspring

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Evolutionarily Stable Strategy
Evolutionarily Stable Strategy (ESS) A
strategy which, if adopted by a population,
cannot be invaded by any alternative strategy
that is initially rare. An ESS is a kind
of Nash equilibrium.
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What is the ESS for a Pathogen?
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What is the ESS for a Pathogen?
A strategy adopted by some kind of pathogen, for
which an alternative (mutant) strategy, cannot
invade.
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What is the ESS for a Pathogen?
A strategy adopted by some kind of pathogen,
for which an alternative (mutant) strategy,
cannot invade.
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What is the ESS for a Pathogen?
A strategy adopted by some kind of pathogen, for
which an alternative (mutant) strategy, cannot
invade.
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What is the ESS for a Pathogen?
A strategy adopted by some kind of pathogen,
for which an alternative (mutant) strategy,
cannot invade.
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What is the ESS for a Pathogen?
A strategy adopted by some kind of pathogen, for
which an alternative (mutant) strategy, cannot
invade.
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What is the ESS for a Pathogen?
A strategy adopted by some kind of pathogen, for
which an alternative (mutant) strategy, cannot
invade.
A strategy that maximizes the Basic Reproductive
Ratio is evolutionarily stable (Anderson and May,
1982)
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ESS for a Pathogen?
What are the evolutionary tradeoffs faced by
pathogens?
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ESS for a Pathogen?
What are the evolutionary tradeoffs faced by
pathogens? Pathogens should evolve to maximize
the transmission rate and minimize the
disease-induced death rate.
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ESS for a Pathogen?
What are the evolutionary tradeoffs faced by
pathogens? Pathogens should evolve to maximize
the transmission rate and minimize the
disease-induced death rate. There must be a
tradeoff between transmission and virulence! ?
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ESS for a Pathogen?
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ESS for a Pathogen?
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ESS for a Pathogen?
Tradeoff between transmission and killing the host
v
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ESS for a Pathogen?
Maximize Ro with respect to v
v
v
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ESS for Multiple Pathogens?
Maximize Ro with respect to v
v
v
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ESS for Multiple Pathogens?
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ESS for Multiple Pathogens?
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ESS for Multiple Pathogens?
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ESS for Multiple Pathogens?
Maximize Ro with respect to v
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ESS for Multiple Pathogens?
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ESS for Multiple Pathogens?
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ESS for Multiple Pathogens?
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ESS for Multiple Pathogens?
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ESS for Multiple Pathogens?
CoESS
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Summary
The evolutionarily stable strategy for a pathogen
is the strategy that maximizes its basic
reproductive ratio Typically, the phenotype that
we consider to be evolving is the disease-induced
mortality rate (virulence) There may be a
tradeoff between virulence and transmission The
ESS level of virulence depends on
coinfection. The host represents a common
property resource, and the Co-evolutionarily
stable strategy is the outcome of a prisoners
dilemma.