Humans certainly get infected with mind-controlling memes. How sure are we that there aren't fungal/bacterial/viral sources of change to human behavior? Maybe an infection could make us more peaceful or warlike, authoritarian or laissez-faire, pious or agnostic, obedient or obstinate. Political and religious movements sure seem to spread like biological infections. I wonder if there are epidemiological measures that could tell the difference. Velocity of spread could be discriminator, but you'd have to test that on populations that are culturally but not physically isolated and visa versa, which is a tall order.