Paranoia is infectious. It’s also an incredibly useful tool. If you can make people afraid enough, uncertain enough, they will simply stop moving.

Madness also makes folks uneasy; they fear contagion.

Panicky fear is more contagious than typhoid or cholera. The atom bombs cause terrible panicky fear. People leave their houses and move to villages.

That’s another thing about ghosts, a very important thing — you have to be careful, because hauntings are contagious. Hauntings are memes, especially pernicious thought contagions, social contagions that need no viral or bacterial host and are transmitted in a thousand different ways. A book, a poem, a song, a bedtime story, a grandmother’s suicide, the choreography of a dance, a few frames of film, a diagnosis of schizophrenia, a deadly tumble from a horse, a faded photograph, or a story you tell your daughter. Or a painting hanging on a wall.

And it is the body's hysterical overreaction to a virus, rather than the virus itself, that makes us ill.

Suicide is contagious.

It must be classed among those phenomena of a hypnotic order, which we shall shortly study. In a crowd every sentiment and act is contagious, and contagious to such a degree that an individual readily sacrifices his personal interest to the collective interest.

I have cultivated my hysteria with pleasure and terror.

Hopelessness can be contagious, but hope can be too. And there is no medicine to match it.

Confidence is contagious. So is lack of confidence.

... courage is as contagious as fear.

Sadly, it is within the religious domain that the phenomenon of rhetorical hysteria takes its most devastating form....

'Global warming' is just the latest in a long line of hysterical crusades to which we seem to be increasingly susceptible.

You can’t stop a mental epidemic. It leaps from person to person across parsecs. It’s overwhelmingly contagious. It strikes at the unprotected side, in the place where we lodge the fragments of other such plagues. Who can stop such a thing? Muad’dib hasn’t the antidote. The thing has roots in chaos. Can orders reach there?