Abstract
Infectious diseases often spread as spatial epidemic outbreak waves. A number of model studies have shown that such spatial pattern formation can have important consequences for the evolution of pathogens. Here, we show that such spatial patterns can cause cyclic evolutionary dynamics in selection for the length of the infectious period. The necessary reversal in the direction of selection is enabled by a qualitative change in the spatial pattern from epidemic waves to irregular local outbreaks. The spatial patterns are an emergent property of the epidemic system, and they are robust against changes in specific model assumptions. Our results indicate that emergent spatial patterns can act as a rich source for complexity in pathogen evolution.
Highlights
Recent studies show that in spatial models, evolutionary dynamics of infectious diseases change with respect to predictions from non-spatial model, which implicitly assume complete mixing of individuals [1,2,3,4,5]
We recently examined a spatial epidemic model in which infection of hosts leads to waning immunity instead of host death [14], and we found that, after the system selforganizes into epidemic waves, natural selection is directed toward increasing outbreak frequency
The reversal in the direction of selection is triggered by a switch in the spatial patterns from epidemic waves to irregular local outbreaks
Summary
Recent studies show that in spatial models, evolutionary dynamics of infectious diseases change with respect to predictions from non-spatial model, which implicitly assume complete mixing of individuals [1,2,3,4,5]. Starting with Rand et al [10], a number of authors have analyzed a spatial pathogen-host model in which a host population with local reproduction is infected by a lethal pathogen that is transmitted through direct local contact [4,11,12,13]. We recently examined a spatial epidemic model in which infection of hosts leads to waning immunity instead of host death [14], and we found that, after the system selforganizes into epidemic waves, natural selection is directed toward increasing outbreak frequency. Frequency selection occurs in spatial competition in chemical reactions [15], autocatalytic hypercycles [16] and parasitoid-host systems [1,17]
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