The genetic structure of human pathogens

Abstract Human pathogen populations are structured by processes including within‐host competition, host–pathogen interaction, selection on the transmission cycle, historic changes in prevalence, and human migratory history. We document examples in which signatures of each process are evident and describe some of the factors that lead one process to dominate over the others. Intuitively, it might be thought that pathogen coevolutionary interaction is so intense that under normal circumstances we might expect that the signature of historic migration is obliterated. However, while this is the case for most pathogens, one pathogen, Helicobacter pylori , provides a signature of migrations, which seems, given current sequencing and analytical technologies, to be at least as informative as human genes.