Human disease agents can get transmitted both horizontally--through infection--and vertically--from parent to offspring. Depending on details of their evolutionary dynamics, they may increase or decrease in virulence over time. The evolutionary dynamics of bacterial transposable elements resembles that of human pathogens in these and other respects. I here briefly highlight similarities and differences in the two evolutionary processes. I also suggest that an epidemiological perspective, combined with future estimates of parameters of transposable element evolution from hundreds of genomes, may yield insights into the forces that maintain transposable elements in bacterial populations.