SUMMARY Motile organisms can expand into new territories and increase their fitness 1–6 , while nonmotile viruses usually depend on host migration to spread across long distances 7–9 . In general, faster host motility facilitates virus transmission 10 . However, recent ecological studies have also shown that animal host migration can reduce viral prevalence by removing infected individuals from the migratory group 11 . Here, we use a bacteria-bacteriophage co-propagation system to investigate how host motility affects viral spread during range expansion. We find that phage spread during chemotaxis-driven navigated range expansion decreases as bacterial migration speed increases. Theoretical and experimental analyses show that the navigated migration leads to a spatial sorting of infected and uninfected host in the co-propagating front of bacteria-bacteriophage, with implications for the number of cells left behind. The preferential loss of infected cells in the chemotactic front inhibits viral spread. Further increase in host migration speed leads to a phase transition that eliminates the phage completely. These results illustrate that navigated range expansion of host can promote the migratory culling of infectious diseases in the migration group.
