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Infectious Insanity

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Being in the stressful hubbub of a psychiatric ward could make you feel even more crazy!

Alice is driven insane just by talking to (or otherwise interacting with) an already insane Bob. If Alice goes insane because of a particular bit of information that drove Bob insane in the first place, it's also an example of Go Mad from the Revelation.

Critical Psychoanalysis Failure is a Sub-Trope, so examples where this happens to psychiatrists trying to help madmen only go there.

Compare and contrast Mind Virus, for literal contagions that change the way its victims think; Madness Shared by Two, where two people develop the same delusion (but may have done so independently); Contagious Cassandra Truth, where the "mad" people are actually delivering a truth no one else believes; and Go Among Mad People, where this is invoked on purpose... and very often becomes this trope, either because madness is really infectious or just because of the level of "care" in the particular Bedlam House.


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    Anime & Manga 
  • In one of the TIPS of Higurashi: When They Cry's Meakashi-hen, Kumagai discusses this trope with Ooishi regarding Shion's diary, along with Despair Event Horizon.
    "It's a diary of a lunatic. Even the ones reading it were becoming insane. That last page, I'm sorry for being born, ...would make even the people reading this jump to their deaths..."
  • Since the "criminal coefficient" that makes you a criminal in Psycho-Pass 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. When some people fake their displayed crime coefficient to go on a crime spree, the populace goes absolutely nuts in fighting them back.
  • Hao from Shaman King 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.
  • When Asura is released in Soul Eater, his madness infects people across Shibusen, most notably Stein. It's later revealed that all the Great Old Ones have this power on a global scale, including Excalibur and Death.

    Comic Books 
  • In Johnny the Homicidal Maniac and I Feel Sick, Johnny and Devi go on a date. Later, we find out that the painting that's been talking to her is part of the supernatural insanity that Johnny has.

    Fan Works 
  • In The Dark Lords of Nerima, Beneda was originally a weak and cowardly youma who tried to use Ranma and his circle of associates as a means of getting back into the good graces of the Dark Kingdom. However, after Becoming the Mask and spending enough time around people who are barely slowed down by helpless odds, their thinking rubs off on her and leads her to attack an enemy that she'd previously been scared to death of.
  • In the The Two-Faced Turnabout, the Joker is called as a witness to the night that an Arkham guard was killed, and Athena Cykes uses Widget to read his emotions when examining his testimony. Phoenix warns Athena to be careful about reading Joker, and it seems the trope is in effect when Athena starts calling Joker "Mr. J" and acts friendly and even flirty with him. It is later subverted, as it turned out to be an act by Athena. As a psychology student, Athena had already read about Dr. Harleen Quinzel falling for the Joker and becoming Harley Quinn, so she recreated Harley's fall to madness to get Joker to loosen up.

    Film — Animation 
  • Dragon Ball Z: Broly – The Legendary Super Saiyan: Paragus was a relatively normal Saiyan with more empathy than most before his son was born. When his son was proven to be abnormally strong, King Vegeta tried to have them both murdered so they wouldn't challenge his Throne. Broly more or less went insane from the combination of his first memory of Goku crying, almost being executed, having to escape Frieza blowing up the planet, and from his own unbelievably strength and sense of superiority that came with it. After years of raising a son that would occasionally hurt or even try to kill him, Paragus started to lose it. As Broly was the only person he had left, he couldn't abandon him, but the danger he posed to Paragus and the universe backed Paragus into a corner. As he tried to put on the crown to control Broly, his son woke up dazed and confused and childishly called after his father. They got into a struggle and Paragus got the crown on, but Broly had worked himself into a frenzy and almost killed Paragus yet again before the crown took over. Paragus was relieved but saddened by having to do this to his son. Yet as time went on, he went mad with power now that he controlled his son similar to how the power drove Broly insane.

    Film — Live-Action 
  • 12 Monkeys: "Telephone call? Telephone call? That's communication with the outside world. Doctor's discretion. Nuh-uh. Look, hey - all of these nuts could just make phone calls, they could spread insanity, oozing through telephone cables, oozing into the ears of all these poor sane people, infecting them. Wackos everywhere, plague of madness."
  • In Ernest Saves Christmas, 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.

  • Discworld:
    • In 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'snote . 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.
    • In The Amazing Maurice and His Educated Rodents, this trope applies to fear and panic among the Clan of Talking Animal rats. Because rats rely so heavily on their sense of smell and have the 'flight-over-fight' instincts of prey animals, merely smelling the fear-pheromones of scared fellow-rats makes them terrified and unable to think rationally.
  • In "Entry Taken from a Medical Encyclopaedia" (also known as "Buscard's Murrain") by China Miéville, when a specific word is spoken with the correct pronunciation, the speaker is infected and will continue to speak the word out loud.
  • The first story in The Martian Chronicles deals with a telepathic society in which insanity is highly contagious. As a result, when you think someone is crazy (because they're claiming to be from another planet, for instance), the automatic reaction is to shoot them immediately — and possibly then shoot yourself, just to be on the safe side.

    Live-Action TV 
  • Cheers: It's played for laughs, but it's generally suggested that the bar itself does something like this on occasion, especially the inane conversations of Norm and Cliff. Carla certainly believes so, trying to warn Boston Celtics player Kevin McHale about getting involved (alas, by the time she does, it's too late).
    Carla: I knew this guy, he was a respected psychiatrist. It's too late for him, but I can still save you.
  • Since Criminal Minds frequently deals with the criminally insane, this pops up from time to time. Mostly among families, where a genetic component could very well be in play. There's also the general idea that their line of work could be doing this to the team (in a "the Abyss stares back" sort of way).
    • Downplayed but important in "The Fisher King, Part 1 & Part 2". The unsub was already mentally ill to begin with, which is why he voluntarily entered a psychiatric facility. But talking with one of the other patients there (Reid's mother) solidified and furthered his delusions. Mrs. Reid accidentally managed to convince him that her son and his colleagues were analogues to King Arthur's knights and that his daughter Rebecca was a metaphor for happiness, which caused him to abduct Rebecca and set a deadly quest for the BAU team in the sincere belief that doing so would heal his wounds.
    • "Heathridge Manor" features a woman who believed that the devil had claimed her fellow actresses as his wives, so she attacked them and then disfigured her own daughter so the devil wouldn't come for her. Her son and daughter internalized those delusions, leading them to team up and kill "the Devil's wives" — random women the son painted while a delusion of his mother spoke to him. The last shot of the episode is the daughter taking the hand of what she believes to be the devil himself (in reality, there's no one there). Prentiss outright says that the titular house "breeds delusions".
  • Farscape: In "Coup by Clam", Space Madness is treated as an infectious disease and anyone suffering from it is killed. A doctor blackmails the crew of Moya by giving them similar symptoms, and promising the antidote if they pay up.
  • In the Firefly episode "Bushwhacked", it is shown that this can happen to survivors of Reaver attacks. The horror of the experience drives them into becoming Reavers themselves.
  • A mild case in The George Burns and Gracie Allen Show: anybody who spends more than a couple of minutes talking to Gracie starts getting confused about what they're talking about.
  • Star Trek: Strange New Worlds:
    • In "Ghosts of Illyria", the crew is exposed to an illness that makes them addicted to light and each crew member becomes gradually unhinged, except Una, who is protected by her Illyrian physiology and becomes the one who saves the day but at the cost of revealing her true ethnicity.
    • In "Lost in Translation", when the crew is having trouble getting a nebula refinery online Pelia correctly suspects sabotage. Meanwhile Uhura is having memory and cognition problems thanks to hearing a Brown Note. The saboteur turns out to be a crew member named Lt. Ramon, who is having the same symptoms as Uhura. He goes insane and spaces himself trying to destroy the refinery. Uhura fears she will suffer the same fate, but with the help of Kirk, she realizes that aliens who live in the nebula and are being killed by the refinery are crying out for help.
  • The Twilight Zone (1985): In the episode "Need to Know", insanity is spread throughout a small town by the repeated utterance of the meaning of life.

    Tabletop Games 
  • Delta Green:
    • One of the plots of MAJESTIC-12's Project OUTLOOK is to create a "psychological virus", a way of causing a cascading spiral of riots and unrest through manipulation of the media.
    • Hastur. Unlike vanilla Call of Cthulhu, Hastur is not an Elder God or Old One, but an infectious and pervasive force of decay. Knowing about Hastur or its related mythos trappings allows such decay to happen on a person's psyche, and "infected" people will become a vector in spreading Hastur's influence. Even worse is that it can infect places too, which also become "insane" in their own way. Both places and people can infect eachother and vice-versa, until they are affected enough and get pulled to the city of Carcosa.
  • In Dungeons & Dragons, the degenerate Kuo-Toa suffer from this as a result of centuries of inbreeding and the cruel regime of their patron deity. A Kuo-Toa who suddenly snaps during a religious rite or the stress of everyday life can inspire homicidal outbursts in its neighbors, so a special caste called Monitors closely watches a settlement's population for any signs of madness and exiles those whose sanity begins to break. These crazed Kuo-Toa fend for themselves on the settlement's periphery and act as the first line of defense adventurers will encounter. In other cases, Kuo-Toa clerics, called Whips, will imprison insane Kuo-Toa in dungeons beneath the temples of Blibdoolpoolp, ready to unleash them upon any trespassers — and the maddened howls of these prisoners add a unique flavor to religious services.
  • Old World of Darkness/Chronicles of Darkness:
  • Warhammer 40,000:
    • The Blood Angels have a lovely case of this known as the "Black Rage". It's literally the psychic imprint of their gene-father the Primarch Sanguinius fighting almost to death in defense of the Emperor's Palace during the Horus Heresy, 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 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.
    • The ancient C'tan curse that created the original Necron Flayed Onesnote  is contagious, and non-infected Necrons stay well clear of Flayed Ones when they appear and sometimes even kill them to keep the curse from spreading.
    • Ork special character Mad Dok Grotsnik is so bloodthirsty that any Orks around him get caught up in his madness, so not only is he and his unit Fearless, unlike other special characters he can't leave a squad he's joined until he's the last one in it.
  • Warhammer: Age of Sigmar: Flesh Eater Courts are created as a result of this trope: an Abhorrent Ghoul King is a particular kind of devolved, debased vampire, more like a raving flesh-hungry beast, but they're also all hopelessly deluded into believing that they're actually regal and noble kings presiding over courts of heroic and resplendent knights. Thus, when they come across communities, particularly those who've already engaged in cannibalism out of desperation or starvation, their delusions spread, and whole groups of people get swept up into the Ghoul King's internal narrative as a Shared Mass Hallucination, and become his "court" seeing themselves as noble soldiers and heroic warriors, all while outwardly degrading into deformed, cannibalistic savages.

    Video Games 
  • The backstory of The Elder Scrolls has Emperor Pelagius the Mad. Infamous for his eccentricities, Pelagius was prone to severe mood swings and outbursts of Ax-Crazy violence. He did not show signs of madness as a child, being perfectly personable. However, his madness crept in when he moved to Castle Solitude, which was still said to be infected by the madness of his aunt, the Wolf Queen Potema.
  • The entire reason the title Big Bad of Slender exists. 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. And people, inevitably, get dragged into it by accident, too. And with the games, there's the chance that he is bleeding over into this world. Just a possibility, of course, but still... Paranoia Fuel, much?
  • In the Warcraft lore and World of Warcraft, it seems like any time a dragon Aspect goes bonkers, almost everyone else in the dragonflight are afflicted with the same insanity their leader/king/parent/etc. has been. They don't even have to be near or around the cause of their leader's corruption into insanity; they just seem to be like some sort of magical or psychological sponge when it comes to their Aspect. The only non-evil black dragons around are the ones who were brought up in another dimension, which presumably removed them from Deathwing's influence.

  • This is one of the creepiest aspects of Homestuck's Trickster Mode. First starting off as a Psycho Serum affecting only person, it's shown to spread upon physical contact with the uninfected.
  • On the second page of A Miracle of Science, the Trope Namer of Science-Related Memetic Disorder, the antagonist is shown acquiring an infection of SRMD from reading a book, Crank Theories in Robotics. Mars, which is a sort of Hive Mind formed from everyone on the planet using Electronic Telepathy, is also very worried about what might happen if a Martian were to come down with it.
  • Stand Still, Stay Silent: Infection by a Kade results in being its puppet for a time before eventually joining its Mind Hive. Before that point, eye contact between a Kade puppet and normal person results in the normal person becoming a puppet themselves.

    Western Animation 
  • In Adventure Time, 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. However, the Ice King's origin is later 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 — and Fionna and Cake is a Show Within a Show that Ice King wrote.
  • Two unfinished Invader Zim would have shown a cross between this and a Computer Virus.
    • In "Ten Minutes to Doom", after Zim's PAK comes off, Dib takes it, and it later attaches itself to his chest. He starts acting like Zim, saying that he's going to take over the Earth, calling people filthy humans, and even calling himself Zim.
    • In "The Trial", the Control Brain connects to Zim's PAK to erase it and starts going insane, even declaring Zim the Most Incredible Irken Ever.
  • In the My Little Pony: Friendship Is Magic episode "Party of One", Pinkie thinks her friends don't want to be her friends anymore and so surrounds herself with imaginary friends, using flour bags or turnip-buckets for the bodies. When Rainbow Dash comes over, Pinkie uses her voice to supply the voices for her imaginary friends, and hides behind her "pile of rocks" friend to call Rainbow Dash a chump. Rainbow Dash responds by asking "who are you calling a chump, chump?" to the pile of rocks, as if she were catching some of Pinkie's insanity.

    Real Life 
  • There are forms of certain mental illnesses (such as schizophrenia) that arise from being in contact with a sufferer of another form of the illness. The historical term is folie a deux (literally "madness for two").
  • In the Middle Ages it was believed that all forms of madness were contagious like any other disease. This was exploited by at least one town who didn't want the king to pass through (since they would be liable for a levy) and pretended they were all insane to make his courtiers think again.
    • There's a good possibility that many cases of these were somewhat true, insomuch as poor medieval milling techniques could allow Ergot to infest local bread stores, leaving to fits of unknowingly drug-fueled insanity among entire townships. An Ergot infestation - combined with religious hysteria, is credited as the reason behind the Salem witch trials.
  • Richard Dawkins is the originator of the term "meme" and the concept of memetics. As an avowed atheist, he's written a number of articles and books using his model to liken religion to a disease—even outright labelling it as a "mind virus" in The God Delusion. Calling religion a "mind virus" has subsequently become popular among "New Atheists," who tend to be fans of Dawkins.