History Main / InfectiousInsanity

* In the ''Literature/{{Discworld}}'' novel ''Discworld/{{Hogfather}}'', HEX contracted psychosis after talking to the Bursar, which was something of a backfire since talking to HEX was supposed to ''alleviate'' the Bursar's[[note]]although on one occasion they used HEX to run one of those hokey "therapist" chatbots and it actually managed to confuse him into lucidity, whereupon he accused it of making fun of him[[/note]]. Ridcully, in a flash of insight, convinces HEX that it's been given a very large dose of dried frog pills (the Bursar's normal treatment), which puts it back in working order.

* This is one of the creepiest aspects of ''Webcomic/{{Homestuck}}'s Trickster Mode.

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** Later Malkavia was added to [[TabletopGame/VampireTheRequiem]] as truly contagious madness among vampires, working similar to old Malkavians.

** Later Malkavia was added to [[TabletopGame/VampireRequieme]] as truly contagious madness among vampires, working similar to old Malkavians.

* Hao from ''ShamanKing'' is insane but particularly good at striking people at their emotionally weakest, having built a seemingly random band of spiritually aware random passers-by with otherwise wildly varying ideals. They're all insane in that they all want to kill every non-shaman on Earth, but behave like perfectly normal people around other shamans.

* The Blood Angels from [[TabletopGame/{{Warhammer 40000}} Warhammer 40K]] got a lovely case of this known as the "Black Rage." It's literally the psychic imprint of their gene-father the Primarch Sangiunus fighting almost to death in defense of the Emperor's Palace during the Literature/HorusHeresy, and then ''actually'' dying fighting Horus himself. It tends to make those that share his gene-seed randomly start living out his last moments, which turns them into [[AxCrazy terrifying close-combat assailants]]. It's also almost incurable, taking all but literal divine intervention, and even then it's only happened twice in 10,000 years.

* "Entry Taken From A Medical Encyclopaedia" (also known as "Buscard's Murrain") by ChinaMieville. When a specific word is spoken with the correct pronunciation, the speaker is infected and will continue to speak the word out loud.

Plaguedoctors ran rampant in the streets like some town in the midst of a siege by criminals. The Leaches and the Birds and the Cockroaches and the Jugglers and the Warlocks and the Herblores and the Buzzers and the Adzentils and the Day-Nights and the Catholic Priests. The Criminals also ran rampant, snatching and taking and fleeing and besieging the city. The Rebels ran rampant, and they both consorted.

The Madmen did what they do best. The Flagellants marched beating themselves while the Madmen danced around them singing mad hymns against the Plague, and the Doctors went after them in the parade. And after them grotesque floats of Plague and the Dead and the End of the World.

The Soldiers ran rampant trying to chase them all down. Told to beat them into submission they instead verily thought they had locked them up in hastily constructed prisons that were called Plaguedoctors and Middle Walls. But they also resorted to locking Plaguedoctors up in their Congresses and Criminals up in their Taverns and Rebels up in their Parties and Madmen up in their Bedlams and Congregations up in their Churches and Wall-Crossers up in the Catacombs and Mobs up in the street. And none could hold them.

Spies ran rampant. People rampantly crossed the Middle Wall and they rampantly ran about in the fields picking flowers and going mad with Ergot. And Ergot were beginning to get rampant.

The Barons angrily screamed at their Officials, and like a Plaguedoctor demanded ever harsher measures. They told the people that it were not as it appeared in every street and every home. And they even said they had the matter well in hand.

The Rulers of the City were Confusion, Madness and the Plague.

-The Strange Account of Molst-Karnburg, Anonymous, 1355

* [[spoiler:The entire reason the title BigBad of]] ''{{VideoGame/Slender}}'' exists. [[spoiler:So long as one person knows he exists (or possibly even ''knows about him in fiction'') he will keep showing up. And his victims who go off the deep end go to great lengths to spread knowledge of his existence to the next unlucky soul. [[InvincibleVillain And people, inevitably, get dragged into it by accident, too.]] [[FromBadToWorse And with the games, there's the chance]] [[YourMindMakesItReal that he is bleeding over into this world.]] Just a possibility, of course, but still... ParanoiaFuel, much?]]

* In ''ErnestSavesChristmas'', Ernest and Harmony go in disguise to try and free Santa Claus from jail. By the time they get there, Santa has already convinced the other inmates of his identity (to the point they're singing ''carols!''), which Ernest uses as an excuse to get him out by claiming that his insanity is infectious and he belongs in an asylum.

* In the ''Series/TwilightZone'' episode "Need to Know", insanity is spread throughout a small town by the repeated utterance of the meaning of life.

** Insanity spreading within a dragonflight is questionable. Dragon Aspects are the most powerful members of their dragonflight and are the political and social leaders, but the entire flight is also linked to and responsible for protecting its domain (the earth, for example, or magic), so insanity spreading from the leader and most powerful member of a group to the followers might be [[JustifiedTrope entirely justified]].

** No, anyone who spends a couple of minutes talking to Gracie gets confused. Those who talk to her more than a few minutes risk going completely bonkers. A studio executive who spoke with her required "two strong men" to carry him away to the sanitarium.

** Rabies could count as this.

* When [[spoiler:Asura is released]] in ''SoulEater'', his madness infects people across Shibusen, most notably [[spoiler:Stein]].

* In one of the TIPS of ''VisualNovel/HigurashiNoNakuKoroNi'''s Meakashi-hen, Kumagai discusses this trope with Ooishi regarding [[spoiler:Shion]]'s diary, along with DespairEventHorizon.

* The Blood Angels from [[TabletopGame/{{Warhammer 40000}} Warhammer 40K]] got a lovely case of this known as the "Black Rage." It's literally the psychic imprint of their gene-father the Primarch Sangiunus fighting almost to death in defense of the Emperor's Palace during the HorusHeresy, and then ''actually'' dying fighting Horus himself. It tends to make those that share his gene-seed randomly start living out his last moments, which turns them into [[AxCrazy terrifying close-combat assailants]]. It's also almost incurable, taking all but literal divine intervention, and even then it's only happened twice in 10,000 years.

* In one of the TIPS of HigurashiNoNakuKoroNi's Meakashi-hen, Kumagai discusses this trope with Ooishi regarding [[spoiler:Shion]]'s diary, along with DespairEventHorizon.
-->''"It’s a diary of a lunatic. Even the ones reading it were becoming insane. That last page, [[spoiler:I’m sorry for being born]], ...would make even the people reading this jump to their deaths…"''

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* In ''WesternAnimation/AdventureTime'' With [[DistaffCounterpart Fionna And Cake]], Fionna tells Cake not to touch the Ice Queen's tiara because she "might catch her crazy", which sounds like she's talking about "power corrupting" and whatnot since the tiara (and crown, in the original's case) is the source of her magic power. [[spoiler: But then later the Ice King's origin is revealed and he turns out to have been a sober, buttoned-down archaeologist before he found the crown, which he put on one day while indulging in a silly moment with his girlfriend, and as a direct result of that one act slowly became the Ice King we're familiar with today]].

* Since the "criminal coefficient" that makes you a criminal in ''Anime/PsychoPass'' is heavily affected by stress, latent criminals tend to increase the coefficient of victims and onlookers, especially since people have become so accustomed to uninterrupted peace. [[spoiler:When some people, and the populous goes absolute nuts in fighting them back.]]