Species-level variation in disease burden is common in multi-host disease systems and can promote zoonotic disease emergence, affect persistence of endangered populations, and impact ecosystem stability. Explanations of observed differences in the distribution of disease burden among species sharing a generalist pathogen typically rely on species-level differences in contact structure, behavior, and/or immune defense. However, both demography and seasonality may also contribute to differential disease burden among host species. While the dynamics of one-host disease models are known, as are the dynamics of multi-host disease models with constant birth; seasonal host birth has not been investigated as a potential mechanism of differential disease burden in multi-host disease systems. We used mathematical models to study how the epidemic dynamics of a focal host species with constant births is affected by interaction with a second host species that exhibits seasonal births. We tested how disease dynamics of both species are affected by the amplitude of seasonal fluctuations in birth and the timing of the initial introduction of the disease relative to the birth cycle of the seasonally reproducing species.
Results/Conclusions
While differences in disease burden between hosts are often explained by immunological differences, behavior, or social contact structures, we find that different seasonal birth patterns alone can also drive differences in disease burden over time. Most importantly, we find that the timing of disease introduction relative to annual birth cycles in one species can profoundly influence transient and long-term disease dynamics in both species. When the disease is introduced at the beginning of the birth cycle in the seasonally reproducing species, the magnitude of the epidemic peak and endemic disease prevalence in both species was amplified, whereas introduction of the disease at the end of the seasonally reproducing species’ birth cycle dampened the size of the epidemic peak and endemic prevalence in both species. Therefore, demographic seasonality may explain differences in both the transient and steady-state behavior of otherwise seemingly similar disease systems in nature, since the epidemic dynamics are sensitive to when the disease is introduced into the system. Our study provides qualitative understanding of the effects of species interactions between species with varying seasonality in birth and is an initial step for further work studying the effects of seasonal demography in multi-host disease systems.