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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. Outline of Presentation. Background to Disease Evolution - Evolution of virulence - Antibiotic resistance - Disease emergence
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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
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
Background to Disease Evolution Evolution of Virulence Antibiotic Resistance Disease Emergence
Background to Disease Evolution Evolution of Virulence Antibiotic Resistance Disease Emergence
Background to Disease Evolution Evolution: Achange in genetic material in a population from generation to the next. - We say that organisms evolve to “maximize their fitness”
Background to Disease Evolution Evolution: Achange in genetic material in a population from generation to the next. - We say that organisms evolve to “maximize their fitness” 2. Fitness ≅ Reproductivity
Background to Disease Evolution Evolution: Achange 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
Background to Disease Evolution Evolution: Achange 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
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.
What is the ESS for a Pathogen? A strategy adopted by some kind of pathogen, for which an alternative (mutant) strategy, cannot invade.
What is the ESS for a Pathogen? A strategy adopted by some kind of pathogen, for which an alternative (mutant) strategy, cannot invade.
What is the ESS for a Pathogen? A strategy adopted by some kind of pathogen, for which an alternative (mutant) strategy, cannot invade.
What is the ESS for a Pathogen? A strategy adopted by some kind of pathogen, for which an alternative (mutant) strategy, cannot invade.
What is the ESS for a Pathogen? A strategy adopted by some kind of pathogen, for which an alternative (mutant) strategy, cannot invade.
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)
ESS for a Pathogen? What are the evolutionary tradeoffs faced by pathogens?
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.
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! ?
ESS for a Pathogen? Tradeoff between transmission and killing the host v
ESS for a Pathogen? Maximize Ro with respect to v v* v
ESS for Multiple Pathogens? Maximize Ro with respect to v v* v
ESS for Multiple Pathogens? Maximize Ro with respect to v
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 prisoner’s dilemma.