The Evolution of Virulence: An Ecological Perspective

The evolution of pathogen virulence is a central question in evolutionary epidemiology. This review examines the development of these ideas over the last 75 years from an ecological perspective using a mixture of theoretical and empirical studies. I begin with Fenner’s work on myxomatosis, which led to the key concept that trade-offs exist between transmission and virulence in pathogen life histories. I then consider how models of Fenner’s study gradually developed into a major area of theoretical epidemiology. The emerging concepts were constantly challenged by new empirical studies that illustrated how virulence may be modified by culling, vaccination, and different forms of heterogeneity within and between species and spatial heterogeneity. The emerging field of phylodynamics has provided multiple new tools to analyze and visualize the evolution of virulence and a much broader perspective on the diversity of viruses and their hosts. I conclude with a brief discussion of possible future directions of study.