History Main / BeneficialDisease

* The Vinn Parasite in ''Webcomic/DriveDaveKellett'' re-jiggers its host's DNA through a comorbid retrovirus. This results in [[MakeThemRot cytotoxic venom]], [[ShockAndAwe Bio-electrogenisis]], electropreception, and [[InvisibilityCloak chromatophores in the skin]]. The downside is that the parasite rejiggers the brain and germ cells too, resulting in personality death and sterilization.

** [[http://www.scp-wiki.net/scp-016 SCP-016]] is a disease which [[AdaptiveAbility adapts]] the infected to any life-threatening situation they are put in to keep them alive. For example, if an infected person is locked in a room being flooded with water, they may gain the ability to breath underwater or they may gain increased strength to help them break out of the room.

* In ''VideoGame/MegaManX'', the Maverick Virus is this to Zero. According to WordOfGod, the virus had ironically fixed a programming bug in his "cognitive" system that made him very violent and disobedient, to the point that he performed a HeelFaceTurn soon after and joined the Maverick Hunters to face down other Mavericks. (The virus is supposed to make other robots violent by removing their inhibitions and their empathy). This is even taken into gameplay in ''VideoGame/MegaManX5'', where Zero getting infected by the floating viruses that roam in some stages makes him temporarily invincible (while X instead loses part of his health).

* The Vinn Parasite in ''Webcomic/DriveDaveKellett'' re-jiggers its hosts DNA through a comorbid retrovirus. This results in [[MakeThemRot cytotoxic venom]], [[ShockAndAwe Bio-electrogenisis]], electropreception, and [[InvisibilityCloak chromatophores in the skin]]. The downside is that the parasite rejiggers the brain and germ cells too, resulting in personality death and sterilization.

* For a beneficial parasite example, an attached lamprey in ''VideoGame/ArkSurvivalEvolved: Aberration'' saps your health but prevents radiation sickness. There are less painful ways to block radiation, but if you don't have those and can heal off the damage...

* In ''VideoGame/MegaManX'', the Maverick Virus is this to Zero. According to WordOfGod, the virus had ironically fixed a programming bug in his "cognitive" system that made him very violent and disobedient, to the point where he performed a HeelFaceTurn soon after and joined the Maverick Hunters to face down other Mavericks. (The virus is supposed to make other robots violent by removing their inhibitions and their empathy). This is even taken into gameplay in ''VideoGame/MegaManX5'', where Zero getting infected by the floating viruses that roam in some stages makes him temporarily invincible (while X instead loses part of his health).

* One increasingly common fan theory in ''Franchise/ResidentEvil'' is that constant ''light'' exposure to the series' various mutagenic viruses and substances has given most of the mainstay protagonists the superhuman strength, agility, and endurance they all seem to enjoy in the later games. The developers have [[ShrugOfGod neither strongly supported nor denied this.]]
** Directly confirmed to be the case for Sherry Birkin in ''VideoGame/ResidentEvil6'', however; after being exposed to, and then cured of the G-virus back in ''VideoGame/ResidentEvil2'', her DNA has been modified just enough to give her amazing [[HealingFactor tissue-regenerative capability]] ''without'' turning her into a monster the way it did her father.
** BigBad Alexia Ashford from ''VideoGame/ResidentEvilCodeVeronica'' created the t-Veronica Virus believing it would give her godlike powers if her body was given time to assimilate the virus. [[spoiler:She was right, after fifteen years in cryogenic sleep Alexia was able to fly, use her combustible blood as a projectile, was almost invulnerable, and could psychically control an unknown amount of giant tentacles. It also made her grey and ant-like, but she was too crazy to care.]]
** ''VideoGame/ResidentEvilTheDarksideChronicles'' shows further benefits of the t-Veronica virus. [[spoiler:Manuela Hidalgo was injected with the virus by her father to combat an unnamed illness and (unknowingly) had her infected organs regularly replaced for fifteen years. This cured her original illness and gave her the combustible blood power, though if she uses that power too much it can lead to self-immolation, and it disfigured her right arm.]]

[[folder:Web Originals]]

* Appears several times in the ''VideoGame/TraumaCenter'' series:
** In ''Under the Knife 2'', all strains of Neo-GUILT grant the host benefits such as making them more intelligent, faster, or stopping the aging process. Well, [[DeadlyUpgrade until they get activated, that is...]]

** In ''Trauma Team'', [[spoiler:Naomi Kimishima, already weary from the GUILT she contracted during the events of ''Second Opinion'', gets infected with Rosalia.]] While the parasite formed by the two becomes a deadly threat, it also makes the latter, until then incurable, take a shape that allows CR-S01 to eliminate it with ease.

* The Creator/CoryDoctorow short story "0wnz0red" features co-protagonist Liam, who's been implanted with a retrovirus linked to a microcontroller, essentially allowing [[MasterOfYourDomain bodyhacking]]. What does he do with it?

* The Rot in ''VideoGame/{{Armello}}''; any hero infected with severe rot (especially the king) loses one HP on odd-numbered rounds (morning) and becomes susceptible to the cleansing magics of the Wyld, [[EvilerThanThou but at high levels Rot can be used to overpower the Banes, other Rot players, and the King himself]][[note]]In a Rot battle, whoever has a higher Rot stat gains dice equal to their opponent's Rot stat.[[/note]]

* Matou Kariya from ''Literature/FateZero'' allows himself to be infected with "crest worms" that eat away at his body and will eventually kill him, but infuse him with enough magical power to summon and control Berserker, the strongest class of servant in the Grail War. It's his only hope of winning the Holy Grail and getting his wish granted.

* In the 25th episode of ''Manga/{{Mushishi}}'', "Eye of Fortune, Eye of Misfortune", a woman was blind until a mushi entered her eye and allowed her to see again. Of course, it also eventually allowed her to see through objects and then into the future, before [[spoiler: ''crawling out of her head and taking her eyes with it'']]
* A ''Manga/TokyoMewMew'' episode featured a Chimera Anima with [[{{Fartillery}}a smelly fart attack.]] Mew Pudding just happened to have a cold that day, so...

* ''Animation/KikoRiki'' episode "The Chill" subverts this. Dokko catches a cold and Wally thinks it would be cool to catch one too because that way, he'd get treats. Despite doing everything possible, he fails to catch anything, but gets Krash and Chiko (who were trying to stop him) to feel sick. After he's informed that the two will have to get a lot of shots to get cured, Wally decides that he'd rather stay healthy.

* ''Fanfic/AngerManagement'': Downplayed-- Haiku describes her cold negatively, but likes the pallor it gives her.
* The live vaccine against [[SyntheticPlague synthetic]] HatePlague called Madsen's Hollow in ''Fanfic/ProjectTatterdemalion'' is arguably this. It gives you fuzzy CombatTentacles, {{retractable|Appendages}} [[AbsurdlySharpClaws razor-sharp claws]], [[AlienHair technicolor tendrils]] in place of hair, PsychicPowers, the ability to sense and generate {{EMP}}s and use them to [[InnateNightVision navigate]] and communicate not entirely unlike [[{{Telepathy}} telepaths]] (sometimes to the point of MentalFusion if the tendrils get close enough to interweave); FlashStep, [[GoodThingYouCanHeal an amazing healing factor]], predatory instincts, and [[TrueCompanions instinctively bond with other shinigami]]. Though it's partially {{Justified}} in that Madsen's Hollow gives its victims almost all of those things as well, in addition to driving them insane.
* There's the ''Literature/HarryPotter'' fanfic "[[http://www.fanfiction.net/s/1399984/1/ Recnac Transfaerso]]", where having cancer causes Harry to develop on-off superpowered magic.

* ''Film/{{Doom}}''. The Martian virus either turns you into a horrible monster, or gives you superstrength, limited bursts of speed and insane hand-eye coordination. The monsters know who will get which effects before trying to infect them. [[TheHero Reaper]] didn't know, but he sure benefited from it.
* In ''Film/{{Phenomenon}}'', Creator/JohnTravolta's character develops hyperintelligence and even psychokinesis because of what is eventually discovered to be a terminal brain tumor.
* ''Film/ResidentEvilApocalypse''. Alice gains superhuman strength, speed and agility because the T-virus that infected her has bonded with her on a cellular level.
* According to the {{backstory}} of ''Film/Underworld2003'' is that the original immortal Alexander Corvinus became one after a deadly plague that wiped out pretty much everyone else in the area mutated in his body, giving him eternal life. Later, he had three sons, two of them inherited the active form, while the third was a normal human but with a latent form of the virus. The first two sons, twins, were bitten by a wolf and a bat, further mutating the disease into [[OurWerewolvesAreDifferent lycanthropy]] and [[OurVampiresAreDifferent vampirism]], respectively. Both species have superhuman strength and speed, as well as eternal life and perfect health. The only real disadvantages are weaknesses to silver (Lycans) and UV rays (vampires), although the original Lycans couldn't control themselves, transforming permanently in their lycan form and going on mindless violent rampages.

* ''Literature/AnitaBlake'': Lycanthropy is depicted as a blood-borne disease that kills all other diseases and foreign substances (like toxins) in the carriers. You turn furry once a month, but can't ever get sick with anything else again. It's enough of a disease that there's even a vaccine, though a bad batch can actually turn you into a lycanthrope.
* A Creator/CoryDoctorow short story, "0wnz0red", features co-protagonist Liam, who's been implanted with a retrovirus linked to a microcontroller, essentially allowing bodyhacking. What does he do with it?

* The ''Literature/{{Discworld}}'' series features the talking dog Gaspode, who notes that (like the Mr Burns example discussed below) he suffers from so many diseases (including licky end, which should apparently only be contractable if one is a pregnant sheep) that he's only still alive because they're too busy fighting each other to focus on killing him.
%%* ''Literature/TheDresdenFiles'': At one point, Harry is captured by vampires after he had intentionally consumed a deadly mushroom which would kill if he didn't get medical treatment in a few hours in order to force his evil fairy godmother to let him go, with the result that the vampires can't drink his blood without becoming poisoned.
* In ''Literature/TheFireman'' a deadly spore causes SpontaneousHumanCombustion. It is possible however to control the spore which in turn gives the host the power to create and control fire.
* ''Literature/FoundationSeries'''s ''Literature/FoundationsFear'': The childhood illness of BrainFever is an [[InvertedTrope inversion]] because catching "brain fever" makes one susceptible to R. Daneel's PsychicPowers. Hari Seldon had been lucky enough not to get sick at a young age, which means Daneel could not read his mind.

* ''Series/SesameStreet'''s ''[[Literature/ItsNoFunBeingSick It's No Fun Being Sick]]'': Herry thinks being sick should be useful because you get lots of attention, [[SubvertedTrope but when he does get sick]], he feels bad and can't enjoy said attention.
* Creator/LarryNiven's ''Literature/KnownSpace'' has the Tree-of-Life virus carried by a species of root vegetable native to the Pak homeworld, when Paks reach middle age the roots become irresistible to them and they eat them, becoming infected with the virus and turning into super-intelligent and super strong Protectors single-mindedly dedicated to the preservation of their bloodlines. And since Earth is one of their lost colonies, [[HumanityCameFromSpace humans can become Protectors as well.]]

%%* In ''Literature/NakedLunch'', [[MadScientist Dr. Benway]] discusses curing several terminal catatonics by getting them addicted to heroin.

* Creator/ScottWesterfeld's ''{{Literature/Peeps}}'': Carriers of the parasite enjoy super strength, enhanced senses, and extended lifespan. Unfortunately, most people who get infected become feral with a [[OurVampiresAreDifferent craving for blood]] and aversion to things they loved before their infection. And the parasite is very contagious, kissing is enough to infect someone.
* Creator/NealAsher's ''[[Literature/ThePolity The Skinner]]'': Set on a DeathWorld that has this gigantic leech whose bite carries a virus with interesting properties, "victims" become super-strong and nearly immortal and indestructible. Almost all animals on-planet are infected by it, as are most humans who live there. The real downside is that the evolutionary "purpose" is so predators can have permanent prey, and even if you can't die, it doesn't mean you can't feel pain/suffer a FateWorseThanDeath.
* Two different examples in ''Literature/SuperMinion''. Benedicci is a clear-cut example, as it strengthens the immune system, modifies the brain to understand tinker tech, and in some cases also provides enhanced strength, reflexes, intelligence, or regeneration. In very rare cases these improvements can be strong enough to compete with supers and powerful mutants. Mutavus is less clear-cut, as it will frequently save the lives of people with medical conditions or life-threatening injuries and occasionally grant abilities on par with super powers, but basically all results cause the patient to [[FantasticRacism stand out in a crowd]], And some mutations can put nearby people at risk or have [[BodyHorror other]] [[HorrorHunger serious]] [[FateWorseThanDeath side effects]].
* In ''Literature/TheExpanse'' Holden's chronic cancer makes him immune to the microbes colonizing the vitreus humors of every other human on Illus. Specifically his medication is toxic to them and administering it to everyone else causes their vision to clear up within an hour.

* In the ''Series/BuffyTheVampireSlayer'' season 2 episode "[[Recap/BuffyTheVampireSlayerS2E18KilledByDeath Killed by Death]]", Buffy's flu makes her sick, but also allows her to see the [[MonsterOfTheWeek demon of the week]], which had been killing sick children in the hospital [[FridgeHorror for years.]].
* ''Series/{{House}}'' has used one disease to cure another on more than one occasion. Such as when the teenage faith healer whose touch seemed to cure cancer turned out to have herpes, which attacked tumors.

* An episode of ''Series/{{Smallville}}'' featured a little boy with a brain tumor that gave him telepathy. It's revealed to be fatal in a later episode, however, and they are unable to reach an expert who could possibly save him before it's too late.

[[folder:Puppet Shows]]
* ''Series/SesameStreet'': In one episode, Telly gets something called "triangle-sneeze-[[SomethingItis itis]]", which makes him sneeze whenever a triangle is near. However, this is the only symptom so it's not like he has to rest or anything, and the sneezing comes in useful when they use it to find some valuable triangular objects.
[[/folder]]

* ''FAPP'' ({{NSFW}}): Every living thing in the world of Jizzral, or those that enter it, are infected by a phenomenon called "the Fappening"; it causes those affected by the infestation to quickly recover from any injury at such a speed that they're practically immortal, receive abnormally increased sexual urges, and undergo random and strange physical mutations that often fall into the lewd area. There is no cure (at least, not any known ones), and the effect is spreading to many other worlds, and yet it does not seem malicious since the inhabitants of Jizzral consider it natural.

%%** There's also an interesting interaction with the Toxic effect and Dung Pies. In Blighttown, certain enemies shoot toxic darts at you. This inflicts a devastating damage over time effect that is usually a death sentence unless you have the curative item. There's an item called Dung Pies, however, which inflict a much less harmful "strain" of the same effect. If you're on the verge of being infected by Toxic, quickly using a Dung Pie will infect you with the less harmful strain, which is much easier to survive and, unlike curing it outright with your limited healing items or spells, [[OneCurseLimit prevents you from getting it again]] for a little while.

* ''VideoGame/EternalSonata'': ALL diseases in Chopin's dream world. Any fatal illness gives the victim access to magic, leaving them pariahs but capable of surviving heavy-duty combat in lacy skirts.
%%* In ''VideoGame/FinalFantasyXI'', having a damage-over-time effect on you prevents all standard forms of Sleep by instantly waking you each time the damage ticks. For many [=NMs=] that utilized Sleep inducing attacks it was common practice to chug Poison Potions.
* [[VideoGame/StarcraftII Stukov]] in ''VideoGame/HeroesOfTheStorm'' has the ability to spread a virus that heals his teammates.

* This is part of the quarians' backstory in ''Franchise/MassEffect''. As their home planet was full of beneficial diseases, their immune system grew to be very welcoming to foreign organisms, adapting to the disease rather than fighting it off. After their geth rebelled and drove them from the homeworld, this became a fatal weakness, so they were forced to live in personal containment suits and keep their spaceships like a clean room.

%%* Not exactly this trope, since Insanity is not a disease, but in ''VideoGame/MightAndMagic'' ''VI-VIII'' it causes a significant drop of Personality and Intelligence (that determine the efficiency of Self and Elemental magic) as well as stopping mana regeneration by resting, but the strength of affected party member skyrockets. If it hits your Knight who has zero magical abilities to begin with but makes great use of that strength boost, you're golden.
* ''Franchise/{{Pokemon}}'':
** From Generation II onward, the main video games have had the Pokérus virus. If you're very, very lucky, a wild Pokémon you fight might just spread Pokérus to one of your Pokémon. With this condition, that Pokémon will gain twice as many effort points (effort values are a complex hidden stat-growth mechanic, look it up) when an enemy mon is defeated. Basically, it will save you time when trying to fine-tune your Pokémon's stats. It can be spread to any Pokémon in the trainer's party who hasn't been infected before. Pokérus does, however, "cure" after so many hours of play, and though the effect never goes away, it can't be spread anymore. A way to avoid this is to keep a Pokémon with the virus in your PC, where Pokérus will stay active indefinitely.
%%** Related, though not precisely this trope (since they aren't exactly diseases per se): Pokémon can only have one of six [[StatusEffects non-volatile status ailments]]: Burn, Freeze, Paralysis, Poison, bad Poison (most prominently from the move Toxic), and Sleep; with the exception of a Poisoned Pokémon becoming badly Poisoned, or using Rest to replace one of the other ailments with Sleep, it's impossible for an enemy Pokémon to inflict a different one of the six on a target. Thus there are strategies like having a Pokémon hold a Flame Orb (which gives it the Burn status at the start of battle) to prevent other, more limiting status ailments from being applied. Some effects, such as Poison Heal also make these status beneficial on top of granting immunities to the others.

*** ''VideoGame/ResidentEvilTheDarksideChronicles'' shows further benefits of the t-Veronica virus. [[spoiler:Manuela Hidalgo was injected with the virus by her father to combat an unnamed illness and (unknowingly) had her infected organs regularly replaced for fifteen years. This cured her original illness and gave her the combustible blood power, though if she uses that power too much it can lead to self-immolation, and it disfigured her right arm.]]

** In ''Under The Knife 2'', all strains of Neo-GUILT grant the host benefits such as making them more intelligent, faster, or stopping the aging process. Well, [[DeadlyUpgrade until they get activated, that is...]]

* The Armed Virus from the [[VideoGame/ValkyrieDriveBhikkhuni Valkyrie Drive]] [[Anime/ValkyrieDriveMermaid Project]] gives enhanced physical capabilities to its hosts and allows them to turn into powerful weapons when aroused.
* In ''VideoGame/{{Fallout}}'', the US government [[SyntheticPlague tried to engineer one]] as part of the Pan-Immunity Virion Project, intending to create an actively evolving antidote to the New Plague ravaging the world and to immunize the US against bio-warfare attacks by China. When they discovered the potency of its MutagenicGoo properties, they scrapped that project, renamed it the Forced Evolutionary Virus, and tried to use it as a SuperSerum. This... did not work out so well, leaving the fanbase split on exactly how extensive a role FEV played in creating the various NuclearMutant creatures of post-apocalyptic America.
* Vampirism in ''VideoGame/Castlevania64'' might take away your primary weapon and ability to recover health by eating food, but it also ''makes you unable to die''. You still take damage, but you keep going even when your health reaches zero. As long as you keep in mind that you'll get a NonStandardGameOver if you remain in vamp status until next midnight, it can be situationally useful if you keep an eye on the clock and keep a Purifying Crystal on hand. It best comes into use when forced to navigate the [[ThatOneLevel odious Garden Maze]] and its invincible DemonicSpiders, since you handily fight a vampire ''immediately'' before entering the maze...
%%* Technically it's poison, not a disease, in ''VideoGame/UltimaIV'', but being poisoned does have the side effect of making anyone who has it immune to sleeping spells -- which is immensely useful in a part of the Great Stygian Abyss, where the party is confronted by multiple Balrons chain-casting sleep spells.
* For a beneficial parasite example, an attached lamprey in ''VideoGame/ArkSurvivalEvolved: Aberration'' saps your health but prevents radiation sickness. There are less painful ways to block radiation, but if you don't have those and can heal off the damage...
* ''VideoGame/{{Griftlands}}'': The Bog Parasites[[note]]acquired on Day 2 of Rook's campaign or brawl[[/note]] are generally a harmful nuisance, as they take up a card in your decks and usually deal 1 damage when they're drawn. However, draw and/or use them enough times and they 'Hatch' into special-effect cards.

[[folder:Web Comics]]
* The Vinn Parasite in ''Webcomic/{{Drive|DaveKellett}}'' re-jiggers its hosts DNA through a comorbid retrovirus. This results in [[MakeThemRot cytotoxic venom]], [[ShockAndAwe Bio-electrogenisis]], electropreception, and [[InvisibilityCloak chromatophores in the skin]]. The downside is that the parasite rejiggers the brain and germ cells too, resulting in personality death and sterilization.
* ''Webcomic/ManlyGuysDoingManlyThings'': According to Commander Badass, everyone in the future has cancer. It's such an integral part of their bodies that future humans have formed a symbiotic relationship with it to the point that cancer has stopped being dangerous and instead functions as a minor HealingFactor.

* One {{Webcomic/xkcd}} strip(#938) comments on a medical trial where the doctors tried to use HIV to treat leukemia.

[[folder:Web Original]]
* On ''Website/{{Neopets}}'', it's not unheard of to deliberately infect a pet with a disease with an inexpensive cure to get rid of a different disease with a more expensive cure, since pets can only have one illness at a time.

* ''WesternAnimation/{{Futurama}}'', "[[Recap/FuturamaS3E2ParasitesLost Parasites Lost]]": Eating a bad sandwich gives Fry worms that rebuild his body, making him stronger, smarter and irresistible to the woman of his dreams. However, Fry got rid of them after he realized Leela only loved him because they changed him.
* Played with in the ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' episode "The Cutie Pox". The titular illness makes Apple Bloom able to do amazing things like [[FluffyTamer tame lions]] and [[GoodWithNumbers do complex equations]], and it seemingly prevents her from getting tired as she tap-dances all night without seeming tired even afterwards. However, it also forces her to do those things, making day-to-day life difficult.
* Downplayed the ''WesternAnimation/PinkyDinkyDoo'' episode "Polka-Dot Pox". While Pinky and her classmates do have to stay home from school due to having the titular disease, its only symptom is [[PolkaDotDisease polka dots on the face]] and it gives them the excuse to throw a "polka-dot party".
* ''WesternAnimation/TheSimpsons'': Mr. Burns is apparently alive only because he's got so ''many'' diseases that they're all blocking each other out from outright killing him.

'''Doctor:''' Oh, no, ''no.'' In fact, even a slight breeze could...\\

* In ''VideoGame/MegaManX'', the Maverick Virus is this to Zero. According to WordOfGod, the virus had ironically fixed a programming bug in his "cognitive" system that made him very violent and disobedient, to the point where he performed a HeelFaceTurn soon after and joined the Maverick Hunters to face down other Mavericks. (The virus is supposed to make other robots violent by removing their inhibitions and their empathy).

** [[https://www.youtube.com/watch?v=qD6fmHUXBEg SciShow has a video on the topic of the health benefits of worm infections.]] They recommend that you DontTryThisAtHome unless it is prescribed by a doctor.

* The Vinn Parasite in ''Webcomic/{{Drive|DaveKellett}}'' re-jiggers its hosts DNA through a comorbid retrovirus. This results in [[MakeThemRot cytotoxic venom]], [[ShockAndAwe Bio-electrogenisis]], electropreception, and [[InvisibilityCloak chromatophores in the skin]]. The downside is that the parasite rejiggers the brain too, resulting in personality death.

%%* ''Literature/TheDresdenFiles'': At one point, Harry is captured by vampires while dying of poison, with the result that the vampires can't drink his blood without becoming poisoned.

* ''Literature/TheDresdenFiles'': At one point, Harry is captured by vampires while dying of poison, with the result that the vampires can't drink his blood without becoming poisoned.

* In ''Literature/NakedLunch'', [[MadScientist Dr. Benway]] discusses curing several terminal catatonics by getting them addicted to heroin.

* One the abducted women in the ''Series/CriminalMinds'' episode "[[Recap/CriminalMindsS5E12TheUncannyValley The Uncanny Valley]]" was diabetic, which somehow allowed her to metabolize the paralytic drugs she was given at a faster than usual rate. [[TruthInTelevision The show did state that there was a significant chance of the drugs being absorbed into her system faster, killing her in less than a day, however.]]

* ''Series/TheOuterLimits1995'': In "[[Recap/TheOuterLimits1995S6E20Nest Nest]]", the polar mites are unable to survive in Robby Archer's body as he suffers from polycythemia, which leads to an overabundance of red blood cells.

* ''Series/StargateSG1'':
** In "[[Recap/StargateSG1S1E4TheBrocaDivide The Broca Divide]]", Daniel and Dr. Fraser's allergies make them immune to the week's malady because of the antihistamines they take, [[spoiler:conveniently preventing the only two named characters with the skills and knowledge to synthesize a cure from being afflicted by the evolutionary regression that turns everyone else into cavemen]].
** In "[[Recap/StargateSG1S4E3Upgrades Upgrades]]", the characters receive a number of armbands that bestow superpowers on the wearers. They work by infecting the wearer with a nanovirus that causes the changes. Unfortunately, this means that the armbands only work for as long as it takes the body to develop an immunity to the virus.

** From the 3.5[[superscript:th]] edition Monster Manual spin-off, ''Fiend Folio'', among the Fiendish Symbionts are parasites from the lower planes such as the gutworms and soul ticks. They have drawbacks -- like slowly turning good characters mad, and generally tempting non-evil ones into evil acts -- but also confer some advantages.

** There's also an interesting interaction with the Toxic effect and Dung Pies. In Blighttown, certain enemies shoot toxic darts at you. This inflicts a devastating damage over time effect that is usually a death sentence unless you have the curative item. There's an item called Dung Pies, however, which inflict a much less harmful "strain" of the same effect. If you're on the verge of being infected by Toxic, quickly using a Dung Pie will infect you with the less harmful strain, which is much easier to survive and, unlike curing it outright with your limited healing items or spells, [[OneCurseLimit prevents you from getting it again]] for a little while.

* In ''VideoGame/FinalFantasyXI'', having a damage-over-time effect on you prevents all standard forms of Sleep by instantly waking you each time the damage ticks. For many [=NMs=] that utilized Sleep inducing attacks it was common practice to chug Poison Potions.

* Not exactly this trope, since Insanity is not a disease, but in ''VideoGame/MightAndMagic'' ''VI-VIII'' it causes a significant drop of Personality and Intelligence (that determine the efficiency of Self and Elemental magic) as well as stopping mana regeneration by resting, but the strength of affected party member skyrockets. If it hits your Knight who has zero magical abilities to begin with but makes great use of that strength boost, you're golden.

** Related, though not precisely this trope (since they aren't exactly diseases per se): Pokémon can only have one of six [[StatusEffects non-volatile status ailments]]: Burn, Freeze, Paralysis, Poison, bad Poison (most prominently from the move Toxic), and Sleep; with the exception of a Poisoned Pokémon becoming badly Poisoned, or using Rest to replace one of the other ailments with Sleep, it's impossible for an enemy Pokémon to inflict a different one of the six on a target. Thus there are strategies like having a Pokémon hold a Flame Orb (which gives it the Burn status at the start of battle) to prevent other, more limiting status ailments from being applied. Some effects, such as Poison Heal also make these status beneficial on top of granting immunities to the others.

* Technically it's poison, not a disease, in ''VideoGame/UltimaIV'', but being poisoned does have the side effect of making anyone who has it immune to sleeping spells -- which is immensely useful in a part of the Great Stygian Abyss, where the party is confronted by multiple Balrons chain-casting sleep spells.

** The Foundation notes that people with diabetes are somehow immune to[[http://www.scp-wiki.net/scp-081 SCP-081]], a virus that causes SpontaneousHumanCombustion.

* Botrytis cinerea is a fungus that affects many plant species. While the resulting fungal infection can destroy crops, if wine grapes are infected under the right conditions, it becomes what winemakers call "Noble Rot", and results in highly desirable dessert wine.

This trope is related to diseases that can be cured by either a medical treatment or the body's self-defense mechanism. The characters may elect to not cure or prolong the infection to gain the maximum benefit from the disease. For immunity/superpowers arising from disabilities of a more permanent nature, (disabilities caused by genetic mutations, accidents or general inborn traits), see DisabilityImmunity. For example, '''sickle-cell anemia that arises because of a genetic mutation resulting in lowered life expectancy, but also provides a degree of immunity against malaria, is Administrivia/NotAnExample of this trope'''. It is an example of Disability Immunity, since sickle cell anemia is permanent. On the other hand, cowpox, which is a disease that provides immunity to a much deadlier disease called smallpox, is a good example of this trope.

* Matou Kariya from ''LightNovel/FateZero'' allows himself to be infected with "crest worms" that eat away at his body and will eventually kill him, but infuse him with enough magical power to summon and control Berserker, the strongest class of servant in the Grail War. It's his only hope of winning the Holy Grail and getting his wish granted.

* One the abducted women in the ''Series/CriminalMinds'' episode "The Uncanny Valley" was diabetic, which somehow allowed her to metabolize the paralytic drugs she was given at a faster than usual rate. [[TruthInTelevision The show did state that there was a significant chance of the drugs being absorbed into her system faster, killing her in less than a day, however.]]

* ''Series/TheOuterLimits1995'': In "Nest", the polar mites are unable to survive in Robby Archer's body as he suffers from polycythemia, which leads to an overabundance of red blood cells.
* Possible TropeCodifier in the ''Series/RedDwarf'' episode "Quarantine", which features the crew discovering various positive viruses such as "Luck", "Joy", and "Sexual Magnetism". ([[CasanovaWannabe Cat]] comments: "Sexual magnetism's a virus? Then get me to a hospital, I'm a terminal case!") They are used in a later episode to help our heroes escape (and Rimmer uses Sexual Magnetism for... well, it's obvious.)

** In "The Broca Divide", Daniel and Dr. Fraser's allergies make them immune to the week's malady because of the antihistamines they take, [[spoiler:conveniently preventing the only two named characters with the skills and knowledge to synthesize a cure from being afflicted by the evolutionary regression that turns everyone else into cavemen.]]
** In "Upgrades", the characters receive a number of armbands that bestow superpowers on the wearers. They work by infecting the wearer with a nanovirus that causes the changes. Unfortunately, this means that the armbands only work for as long as it takes the body to develop an immunity to the virus.

* The Vinn Parasite in ''Webcomic/{{Drive|DaveKellet}}'' re-jiggers its hosts DNA through a comorbid retrovirus. This results in [[MakeThemRot cytotoxic venom]], [[ShockAndAwe Bio-electrogenisis]], electropreception, and [[InvisibilityCloak chromatophores in the skin]]. The downside is that the parasite rejiggers the brain too, resulting in personality death.

* There exists a virus that infects the Marine [[https://en.wikipedia.org/wiki/Flagellate Flagellate]] ''Cafeteria roenbergensis'' (simply called the ''Cafeteria roenbergensis virus'' or ''crov'' for short) that's normally 100% fatal to the Flagellate. The exception happens when it's also infected by the [[https://en.wikipedia.org/wiki/Virophage Virophage]] ''Mavirus'', who will hijack the crov virus's replication process and make it create more mavirus particles instead. This does not only greatly reduce the fatality rate of the infected host, but the Mavirus will also encode itself into the genes of the Flagellate, basically acting like a vaccine against further infections.

** Related to all of this is ''[[https://en.wikipedia.org/wiki/Toxoplasmosis Toxoplasmosis]] [[PuppeteerParasite gondii]]'' -- a parasitic infection that kills fetuses -- but has the side effect of making the host [[CuteKitten adore cats]]. A ''big'' reason the Black Death [[DepopulationBomb depopulated]] Europe (anywhere from 75 million dead to '''200''' million dead!) is the superstition that cats are [[CatsAreMagic agents]] of [[CatsAreMean the devil]] -- and were killed wholesale, leading to population explosions among rats, which did the same to fleas which carried plague bacteria. Humans infected with Toxoplasmosis [[CrazyCatLady befriended and protected cats]], which led to them surviving where their non-carrier neighbors died. One could imagine this resulted in numerous [[BurnTheWitch accusations of witchcraft]], but apparently disease killed cat-killers more effectively than TorchesAndPitchforks killed cat lovers. Hence, Toxoplasmosis infection indirectly protected carriers from ThePlague.

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* In ''Animation/KikoRiki'', the episode "The Chill" subverts this. Dokko catches a cold and Wally thinks it would be cool to catch one too because that way, he'd get treats. Despite doing everything possible, he fails to catch anything, but gets Krash and Chiko (who were trying to prevent him) to feel sick. After he's informed that the two will have to get a lot of shots to get cured, Wally decides that he doesn't want to catch any desease.

* ''Literature/Helliconia'': Humans on Helliconia live with a virus that causes Bone Fever as the climate warms up and the Fat Death as it gets cold. Both plagues carry a terrible death toll, but the survivors are left with changed bodies that are suited to the coming season.

* In ''VideoGame/{{Fallout}}'', the US government [[SyntheticPlague tried to engineer one]] as part of the Pan-Immunity Virion Project, intending to create an actively evolving antidote to the New Plague ravaging the world and to immunize the US against bio-warfare attacks by China. When they discovered the potency of its MutagenicGoo properties, they scrapped that project, renamed it the Forced Evolutionary Virus, and tried to use it as a SuperSerum. This... did not work out so well, leaving the fanbase split on exactly how extensive a role FEV played in creating the various NuclearNasty creatures of post-apocalyptic America.

* ''Wiki/SCPFoundation'':
** The Foundation notes that people with diabetes are somehow immune to the SpontaneousHumanCombustion [[http://www.scp-wiki.net/scp-081 Virus]].

*** There have also been a few cases where patients with AIDS and leukemia were seemingly cured of AIDS after receiving bone marrow transplants from people with a gene that makes them immune to HIV, but they later experienced a resurgence of the virus.

* The live vaccine against [[SyntheticPlague synthetic]] HatePlague called Madsen's Hollow in ''Fanfic/ProjectTatterdemalion'' is arguably this. It gives you fuzzy CombatTentacles, {{retractable|Appendages}} [[AbsurdlySharpClaws razor-sharp claws]], [[YouGottaHaveBlueHair technicolor]] [[AlienHair tendrils]] in place of hair, PsychicPowers, the ability to sense and generate {{EMP}}s and use them to [[InnateNightVision navigate]] and communicate not entirely unlike [[{{Telepathy}} telepaths]] (sometimes to the point of MentalFusion if the tendrils get close enough to interweave); FlashStep, [[GoodThingYouCanHeal an amazing healing factor]], predatory instincts, and [[TrueCompanions instinctively bond with other shinigami]]. Though it's partially {{Justified}} in that Madsen's Hollow gives its victims almost all of those things as well, in addition to driving them insane.

* In ''Animation/KikoRiki'', the episode "How to Catch a Cold" subverts this. Dokko catches a cold and Wally thinks it would be cool to catch one too because that way, he'd get treats. Despite doing everything possible, he fails to catch anything, but gets Krash and Chiko (who were trying to prevent him) to feel sick. After he's informed that the two will have to get a lot of shots to get cured, Wally decides that he doesn't want to catch any desease.