Seasonality and the persistence of vector-borne pathogens

Many vector-borne diseases are affected by the seasonality of the environment. Yet, seasonality can act on distinct steps of the life-cycle of the pathogen and it is often difficult to predict the influence of the periodic fluctuations of the environment on the persistence of vector-borne pathogens. Here we analyse a general vector-borne disease model and we account for periodic fluctuations of different components of the pathogen’s life-cycle. We develop a perturbation analysis framework to obtain useful approximations to evaluate the overall consequences of seasonality on the persistence of pathogens. This analysis reveals when seasonality is expected to increase or to decrease pathogen persistence. We show that seasonality in vector density or in the biting rate of the vector can have opposite effects on persistence and we provide a useful biological explanation for this result based on the covariance between key compartments of the epidemiological model. This framework could be readily extended to explore the influence of seasonality on other components of the life cycle of vector-borne pathogens. Significance statement Does seasonality increase or decrease the persistence of vector-borne diseases? The devil is in the details and our analysis shows that the effect of seasonality depends on which pathogen traits are affected by seasonality. We highlight the contrasting effects of seasonality in the abundance and/or in the biting rate of the vector on pathogen persistence.