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. However, 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.
Joker's Blood and Titan Disease Made a Deadly Disease in Batman; Arkham City. As if he wasn't toxic enough, the Joker's blood is also poisonous.
Although it seemed that Henry was immune, he had succumbed to Joker's blood as the others. However, Henry feigned immunity to gain Batman's trust. Before following Batman's invitation, he met with Harley Quinn and revealed himself as the new Joker.
To motivate Batman to find a cure, Joker infected Batman with his infected blood, and also poisoned the blood transfusion service at the hospital. The four people in the cells at Panessa have received a transfusion of Joker's blood. They're slowly turning into Joker before dying, same as Batman.
Joker Venom is a chemical compound, most typically used by the Joker, that forces the human body to smile and/or laugh uncontrollably. In its most common form, it kills within seconds of exposure and affixes the victim's jaw muscles into a grotesque rictus grin.
There, Batman learns that the unstable properties of the Titan formula are mutating in Joker's blood, gradually killing him. Joker captures Batman and performs a blood transfusion on him, infecting him with the same fatal disease.
Joker's 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's unleashed.
Injustice: Gods Among Us Year 2
Harley reveals to Black Canary that she has a four-year-old daughter named Lucy who is being raised by her sister. After discovering she was pregnant, Harley left the Joker for almost a year to have their baby instead of abortion.
Joker Venom is the Joker's signature weapon. Joker Venom is a toxin, usually dispersed as a gas that makes victims laugh uncontrollably. The Joker himself is immune to the effects of Joker Venom after prolonged exposure to it.
In Joker's case, pseudobulbar affect probably occurred secondary to severe traumatic brain injury (TBI). A number of studies have established that TBI increases the risk of mood disorders, personality changes and substance use disorders.
Much like her son, Penny suffered from an unspecified mental illness. She was responsible for letting her former boyfriend abuse Arthur in his childhood and was temporarily sent to the Arkham State Hospital for unsolicited claims.
At one point, Arthur does visit Arkham State Hospital and reads his mother's file, which says that she adopted him as a child and an abusive boyfriend took advantage of both her and Arthur when he was an infant/toddler.
History. According to the Joker, his father was "a drinker and a fiend". Joker claimed that his father gave him his cheek scars due to his being terrified when his father brutally stabbed his mother sadistically with a kitchen knife when she attempted to use to defend herself.
While fans got to hear many memorable quotes from Joker in Batman: Arkham, the series also revealed what his greatest fear is supposed to be. As it turned out, The Joker feared being forgotten more than anything else because it meant nobody was afraid of him anymore, rendering all his crimes void.
Arthur Fleck is a failed comedian and party clown struggling with mental illness and a laughing disorder. It's later revealed that he actually is sociopathic and gradually begins to become evil as result of his abusive treatment from the people of Gotham City, leading him to become the vengeful anarchist Joker.
Cures. It has been stated that the Joker constantly alters the formula to the Venom (which he is immune to) so no antidote can be prepared for it. However, there have been some antidotes concocted.
Introduction to mainstream DC continuity
Dini also gave Harley new abilities, such as immunity to toxins and enhanced strength and agility, which she received after having been injected a special formula by Poison Ivy.
Arguably the Joker's greatest weakness is his ego, however. He turns to crime to get the attention he desperately craves from Batman.
Believe it or not, this tale saw the Clown Prince of Crime himself become pregnant and give birth to a child. The mother of the child? That was none other than DC's famous magical hero Zatanna, who cast a spell on the Joker after he tried to persuade her to start a family with him.
A spell that backfires gets him pregnant
To make this happen, the most famous clown in comics persuades the wizard Zatanna, however, she wants nothing to do with the Joker and she casts a spell but it backfires and he is the one that becomes pregnant.
Joker Jr. is the son of Harley Quinn and the mass-murdering criminal The Joker.
On the surface, this Joker wants to look “happy.” That's what he's told he's supposed to be. And, his uncontrollable laughing condition is because of how he's been forced to control his anger and sadness; to “stuff it” deep down inside.
His face is indeed white like clowns' faces, but this is because he literally fell into a vat of acid, while real clowns (and the Red Triangle Gang) use face paint. He eschews the clown color scheme and doesn't wear a frilly collar or red nose, instead opting for a sleek purple and green suit.
Image via Warner Bros. Key to Arthur's spiral is new information he learns from his mother Penny (Frances Conroy), with whom he lives. Arthur finds a letter Penny has written to Thomas Wayne, claiming that Wayne is Arthur's real father.