Many animal species migrate seasonally, including those known to harbor zoonotic infectious diseases, yet little is known about how these movement patterns affect host-pathogen interactions. Importantly, host dispersal across a landscape can prevent host population extinction in the face of a debilitating pathogen, and long-distance movements could further allow animals to escape contaminated habitats or cull infected animals from the population.  To investigate relationships between host movement patterns, seasonal habitat use and infection prevalence we used an insect-pathogen system of monarch butterflies (Danaus plexippus) and a neogregarine protozoan, Ophryocystis elektroscirrha. Using field-collected infection data we examined broad-scale associations between monarch movement ecology and population-wide prevalence.  Next, we used spatiotemporal citizen science data collected within eastern N. America to examine how host breeding densities, the duration of habitat use and landscape characteristics affect parasite transmission and accumulation in the hosts’ environment. Third, we developed mathematical models to examine how seasonal movements between breeding and wintering grounds could affect the dynamics of a directly-transmitted specialist parasite such as O. elektroscirrha. 
Results/Conclusions

Results showed that parasites occur in all monarch populations examined to date and prevalence varies dramatically among globally-distributed populations, with highest parasite loads in non-migratory populations in S. Florida and Australia, and low prevalence in N. American migratory populations. Prevalence was similarly low in non-migratory populations sampled in Puerto Rico and Costa Rica, indicating a role for ecological variables other than migration in causing prevalence variation. Analyses of spatiotemporal data in eastern N. America showed that parasite prevalence increases over time within the monarchs’ breeding season. We also examined hotspots of infection within the hosts’ breeding range and ecological variables (host density, patch characteristics) that best predict this fine-scale variation. Finally, modeling results indicated that annual movements between breeding and wintering grounds, as demonstrated by monarchs and other migratory species, can lower parasite prevalence under a limited set of conditions. Collectively, these results are relevant for predicting future changes in the complex relationships between migratory host populations and infectious diseases, including those with human health impacts.