Check out this excerpt from the Epilogue of Crime and Punishment by Dostoevsky. (Bonus, it also has to do with parasites)

"While sick, he had dreamed the whole world was condemned to suffer a terrible, unprecedented and unparalleled plague, which had spread to Europe from the depths of Asia. Except for a small handful of the chosen, all were doomed to perish. A new kind of trichinae had appeared, microscopic substances that lodged in men's bodies. Yet these were spiritual substances as well, endowed with mind and will. Those infected were seized immediately and went mad. Yet people never considered themselves so clever and so unhesitatingly right as these infected ones considered themselves. Never had they considered their decrees, their scientific deductions, their moral convictions and their beliefs more firmly based. Whole settlements, whole cities and nations, were infected and went mad. Everybody was in a state of alarm, and nobody understood anybody; each thought the truth was in him alone; suffered agonies when he looked at the others; beat his breast; wept and wrung his hands. They did not know whom to bring to trial or how to try him; they could not agree on what to consider evil, what good. They did not know whom to condemn or who to acquit. People killed each other in a senseless rage. Whole armies were mustered against each other, but as soon as the armies were on the march they began suddenly to tear themselves apart. The ranks dislashed and stabbed, ate and devoured each other. In the cities the alarm bells rang for a whole day."