Evolution towards Multi-Year Periodicity in Epidemics

We studied why many diseases has multi-year period in their epidemiological dynamics, whereas a main source of the fluctuation is a seasonality with period of one year. Previous studies using a compartment model succeeded to generate a multi-year epidemics when they have a large seasonal difference in a transmission rate. However, those studies have focused on the dynamical consequence of seasonal forcing in epidemiological dynamics and an adaptation of pathogens in the seasonal environment has been neglected. In this paper, we describe our study of the evolution of pathogens sensitivity to seasonality and show that a larger fluctuation in the transmission rate can be favored in the life history evolution of pathogens, suggesting that multi-year periodicity may evolve by natural selection. Our result Our result proposes a new aspect of the evolution of multi-year epidemics.

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