The ecological mechanisms underlying the dispersal of parasites are poorly understood, which is of particular concern in view of currently emerging infectious diseases. In a new study, Pérez-Tris and Bensch examined the distribution and prevalence of avian malaria in a migratory bird across Western Europe. They concluded that repeated independent evolution of year-round transmission has enabled some avian malaria lineages to become more widespread, and more prevalent, than lineages that are transmitted only during the summer. This study blurs the boundaries of evolutionary ecology, epidemiology and macroecology with great potential for cross-disciplinary research.