Seasonal birth pulses are frequently observed in wildlife and are expected to affect the dynamics of infectious diseases within populations. We recently showed that the range of birth pulse shapes observed across mammalian species could have a strong impact on the persistence of diseases, as measured by the critical community size1. Here I present the predictions from our model and investigate the potential consequences of seasonal birth pulses for the evolution of virulence in pathogens. I then discuss the implications for the evolution of life history traits in host species.