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"Two years ago, I uncovered Joker's plot to unleash a genetically-enhanced army on Gotham. The drug he used to modify his henchmen was called Titan. Before I could stop him, Joker ingested a massive dose of the Titan formula and mutated into a gigantic abomination. I managed to defeat him, but his overdose had devastating side-effects. Joker was dying and he needed a cure. To ensure my cooperation, he infected my blood with his own, leaving me no choice but to help him. But that wasn't all. He contaminated Gotham's blood banks too. The result: the patients currently quarantined here. Joker's mutated blood behaves like a prion infection, attacking the brain and transforming these people... into him. Unless we find a way to reverse the process, no-one will be able to stop what he has unleashed."
—Batman on the Joker Infection.

The Joker Infection was a unique condition created by the Joker's mutated blood that slowly turned those infected into direct copies of him.


Before Arkham City[]

Prior to the events of Batman: Arkham City, the chances for a cure to the Titan Disease were looking slim. Joker had the doctors Hugo Strange sent him drain his infected blood and transfuse healthy blood to extend his life while also having Strange send him Mr. Freeze's wife Nora Fries as leverage to get Freeze to develop a cure.

Arkham City[]

Not wanting to go out by himself, Joker blackmailed Strange into sending his tainted blood to hospitals all over Gotham City by reminding him about his experiments with the Arkham Lunatics, Mad Hatter and Quincy Sharp. Joker even managed to poison Batman with his blood forcing the Dark Knight into helping him get the cure for the disease. Unfortunately for Joker, when Batman gained the cure and took his share the Clown Prince of Crime caused him to drop the vial which made the spilled cure lose its potency and fail to heal Joker, Batman then revealed even after all the horrible things Joker did, he would've given him the cure.

Arkham VR[]

After repeated nightmares involving him killing Nightwing and Robin, while attempting to understand them as well as the Joker repeatedly showing up in these nightmares and actually communicating to him in these dreams, Batman realised that Joker's blood had still infected him, although what the effects were weren't known to him. Fearing the infection would take him over as he still had the mad clown's blood in him, Batman would make attempts at pushing away any help from Nightwing and Robin in a conscious effort to keep them safe in the event he would actually lose control and kill them.

Before Arkham Knight[]

Although Batman managed to replicate and distribute the cure, saving thousands of lives as well as rounding up most of Joker's contaminated blood samples with the help of James Gordon, four people were given blood transfusions containing Joker's blood, something that would be discovered far too late by Batman due to hospital errors leaving the transfusions unrecorded. It was sometime afterwards that those individuals began showing signs of the infection leading to their discovery and incarceration by Batman. Through studying the four infected, namely Christina Bell, Albert King and Johnny Charisma Batman would discover exactly what had happened to them, the effects of the Joker's infected blood as well as confirming the reoccurring nightmares he has had.

Batman linked the infection to being a form of Creutzfeldt-Jakob disease (CJD), but it was mutated beyond anything on medical record. Like CJD, the infection attacked the brain and damaged the tissue affecting the victim's mood and behavior. However, this unique infection was not fatal and instead slowly made the host inherit the personality traits and behavior of the Joker until they would likely become a literal copy of the Clown Prince of Crime, although the disease could not change their body structure and/or gender, with Bell, King and Charisma developing the same white skin and, except King, hair color as Joker, with each inheriting different parts of the Joker's personality. Batman would bring Gordon to Panessa Studios, where he was keeping the infected, and reveal that five individuals had been infected with Joker's blood. Batman believes that he and Robin are getting close to finding a cure however, as one of the four infected, Henry Adams, has shown no signs of the Joker Infection manifesting at all, and could actually be immune to the disease. While overwhelmed at the situation Gordon quickly realizes that there were only four of the infected locked up, rather than five as Batman had said there were, unaware that the fifth Joker infected was Batman himself, who has prepared a cell ready in case he fully gives into the infection.

Arkham Knight[]


Fear Toxin allows Batman's Joker personality from the infection to manifest as hallucinations.

To his horror, Batman found Scarecrow's new strain of Fear Toxin could exaggerate the infection to the point of causing hallucinations. In Batman's case a very vivid hallucination of Joker appeared that represented the embodiment of his worst fears and darkest desires along with Scarecrow Nightmares and flashbacks to Joker's past crimes.

Harley Quinn would break into Panessa Studios and free the Joker infected after learning that there were people becoming Joker locked inside, Batman and Robin being aided in finding the infected by an injured Adams, who Quinn had attacked before freeing the infected. However, after stopping Quinn and bringing her back to the main cell room of the studios, Batman and Robin would discover the infected dead, killed by Henry Adams, who Batman realizes had been just like the rest this entire time. Having inherited the more deceitful and manipulative aspect of the Joker's personality, Adams reveals himself to be the one who reprogramed the security system as the reason Quinn was able to break into the studios so easily, having at some point contacted Harley and revealed to her him becoming another Joker, as well as the existence of three others like him. However, just as he's about to shoot Batman Adams discovers he's just as infected as the others were, and believing Batman will be an excellent Joker, he shoots himself in the head, killing both himself and seemingly any hope there had been for a cure.

So far the only known way to cure oneself is to fight the infection from within their mind. The infection took the form of Joker, who Batman was finally able to genuinely scare and lock away in a dark corner of his mind represented by Arkham Asylum's Extreme Isolation, purging himself of Joker's insanity for good. In that case it is heavily implied that Batman exploited the use of Scarecrow's toxin to ensure he could take on the infection. Other than that, a quick death would be needed.

Aside from the obvious adoption of Joker-like traits and to a certain extent hallucinating Joker, the disease also results in the infected having intrusive flashbacks to heinous actions Joker had caused in the past, regardless of whether the infected ever witnessed such actions. In Batman's case it was the crippling of Barbara Gordon and the end of her career as Batgirl as well as bits and pieces of Joker's torture of Jason Todd.

Known Victims[]


  • It was speculated that the very first time Batman showed symptoms of the Joker Infection was right after defeating Mr. Freeze in Arkham City as he hallucinated Joker's face in place of Freeze's while subduing him. This was actually confirmed by Sefton Hill in a Reddit AMA.
    • The first time Batman became truly aware of his infection was in Batman: Arkham VR, since it turned out all the events that took place were part of a nightmare in which he was unknowingly responsible for the deaths of Nightwing and Robin along with blowing up the Iceberg Lounge while imitating Joker.
  • Ironically, the infection enhanced a quality the victim already had:
    • Christina Bell suffered a miscarriage thus losing a baby; she became fixated on Batman.
    • Johnny Charisma was a famous singer; the infection boosted his egomania.
    • Albert King was a professional boxer; he became more violent.
    • Henry Adams was a biology teacher; he came to believe in the survival of the fittest.
    • Bruce Wayne as Batman was more ruthless but refrained from killing, although he implied [see below] that his restraints would disappear if infected long enough. Batman also understood Joker better than anyone resulting in a near-perfect copy. However, the Joker he hallucinated was too consistent and driven, constantly striving to eliminate Batman.
  • Most of the infected resembled alternate versions of the Joker from the comic books.
    • Christina Bell is visually modeled after Earth-37 Bianca Steeplechase from Thrillkiller.
    • Johnny Charisma appears to be modeled after the Joker of Earth-31 (Batman: The Dark Knight Returns). He dresses in a white suit like Joker from this story and is a singer which could be an allusion to Earth-31 Joker.
    • Henry Adams looks like an elderly Joker which could be an allusion to Earth-22 Joker from Kingdom Come.
  • It was never fully revealed what the exact cause for the creation of the infection was other than it originating from Joker's mutated blood.
    • It was probable that the chemicals that caused the Titan Disease (and maybe chemicals already in the clown's blood) caused Joker's blood to mutate, creating the infection.
  • Aside from the two names stated above, Joker referred to the illness as Joker-itis and Mad Clown Disease (a parody of hepatitis and Mad Cow Disease).
    • Batman mentioned that Joker Infection was a variant of Creutzfeldt–Jakob disease that was mutated beyond any medical record.
  • It was shown that despite having cured himself in Arkham City, Batman was still infected by the events of Arkham Knight — considering that Batman only took half the cure and intended to give Joker the other half it could be assumed that was not enough to completely cure him in the long run and was only intended to save him and Joker from immediate death to allow curing later. The hallucination of Joker revealed he had pumped four pints of his blood into Batman which could explain why the cure was ineffective.
  • It is unclear whether or not Joker knew the long-term effects of his blood. While the hallucinated Joker is aware of the effects and implies he knew it all along, it doesn't confirm that the real Joker knew. In addition, Harley shows no signs of the blood's effects thus meaning Joker either didn't know of the disease or didn't trust her sanity enough to infect her.
    • Similarly, it was also not made clear whether the various hallucinations of the Joker were hallucinations or his ghost, although some of the scenes (most notably flashing back to Jason Todd's torture as well as Barbara Gordon's crippling, despite him not being directly present to witness these events) imply that those infected, or at the very least Batman and possibly Henry Adams (the latter of whom mentions "missing [Harley Quinn] too" in his first audio tape despite meeting her for the first time, implying he inherited Joker's memories of Harley Quinn.) managed to at least gain Joker's memories.
  • It is possible that this disease helped inspire an alternate version of Batman known as The Batman Who Laughs, who killed Joker and was subsequently infected by a toxin from within Joker's body, failing to resist and becoming a Jokerized version of himself who went on to jokerize and slaughter countless people, including his family and allies.
    • There is one notable difference as the Joker infection appears to largely suppress the victim's original identity and effectively turn them into Joker copies, while The Batman Who Laughs inherited many of Joker's traits, but never actually considers himself to be Joker.
  • The Joker Infection, as well as gradually stripping Batman of his restraints, was given an indirect allusion at the ending of the Gunrunner Most Wanted mission where Batman, after he subtly threatened to kill Penguin by having him choose between the GCPD or the local morgue after the latter referenced his capture of Nightwing, admitted, when Penguin reminded him of his rule against killing, that the Caped Crusader wasn't feeling himself that night, implying that, if the infection lasted long enough, it would ultimately force Batman to break his one rule. It should be noted that this exchange only happens if the player hasn't surrendered to Scarecrow yet. This could, however, be simply a ploy by Batman to scare Penguin back into line, which nonetheless was the result of Batman's heckling.
  • Another notable side effect of the Joker Infection is the possibility of severe scarring around the areas of the body that had turned as pale like the Joker, however the severity of the scarring differed from person to person; Johnny Charisma was shown to be the most scarred on both sides of his face, while Christina Bell and Albert King showed the least amount of scarring. Out of all the infected however, Henry Adams was the only one not to be scarred, which he would use to his advantage by pretending to be immune to the Joker Disease.