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.
Joker Venom has a variety of depictions over the years, ranging from liquids to gases. In each form, Joker venom causes its victims to laugh uncontrollably and incapacitate them. The venom's effects also causes the victims' faces to turn into rictus grins through the effects on their muscles.
A flashback reveals that before the Joker died, his infected blood was used in blood transfusions, infecting five people including Batman; Batman, concealing his infection from others, imprisoned the four other recipients who were physically and mentally transforming into the Joker.
How Joker's Blood Was Converting Batman Into Joker? Joker's Disease And Blood Infection - Explored
What is Batman's blood type?
Bruce's blood type is AB-. He helped Kate and Maggie with their wedding and got Wonder Woman to officiate it. He wore pastels to it. A young Bruce Wayne found coal in his stocking one year.
While Harley Quinn's immunity to the Joker's toxins is a great benefit for herself, Harley being able to cure others of the villain's sinister serum is something that seriously comes in handy.
In the documentary I Am Heath Ledger (via Digital Spy) it's revealed that, in order to keep the prosthetics in their place as they got loose when he spoke, Ledger had to lick his makeup to keep it in place, and it ended up becoming part of the Joker's manic personality, as well as his most memorable mannerism.
Due to Joker's past of abuse, his pain receptors learned to block pain, and in fact give him a different feeling when ever feeling pain. He could, he was just ignoring it.
If you ask Joker, it's a moot point—as he famously states in Detective Comics #664, a side effect of Joker's tumble into the Ace Chemicals vat is an immunity to all toxins, up to and including fear gas.
Harley's immunity to toxins and enhanced strength and agility, which were gained from a special formula created by Poison Ivy, were carried over from Batman: The Animated Series, with Dini stating that they would give her a sort of "physical edge" over Batman and other heroes.
It is then revealed that the Joker's real name is "Jack Oswald White." Martha then shares that she visited the Flashpoint universe's version of Jack Oswald White, discovering him to be a struggling family man supporting his wife and a child as a janitor at Wayne Casino.
Arthur, as a result of the constant abuse and trauma he had endured, grew up to forget that Penny was apart of this abuse and this resulted in him growing up with her. She began writing letters to Thomas Wayne to get his attention, believing that she once had a relationship with the man.
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.
What happens if you cut your mouth like the Joker?
A Glasgow smile (also known as a Chelsea smile, or a Glasgow, Smiley, Huyton, A buck 50 or Cheshire grin) is a wound caused by making a cut from the corners of a victim's mouth up to the ears, leaving a scar in the shape of a smile.
Narratively, he got a permanent smile scarred into his face just by being born, which is tragic. But cinematically, the idea came from the 1928 silent movie that inspired the character's creation in the first place, The Man Who Laughs (the link to The Batman Who Laughs is clear).
He taunts his victims with pseudo stories of trauma in order to ramp up the tension before he inevitably gets his laugh by maiming or killing someone. The origin of his scars remains a mystery because the Joker doesn't care about how he got them anymore; he merely cares for the effect they have invoking fear in people.
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.
However, his serums did manage to infect Shazam, Blue Beetle, Donna Troy, Hawkman, Supergirl, and Commissioner Gordon (the latter was infected during issue 7 of The Batman Who Laughs miniseries by Scott Snyder).
Contact with Joker venom causes uncontrollable spasms of laughter and then causes a painful death. Some have speculated that the venom hyperstimulates the laughter functions of the brain and the victim is unable to breathe. Prolonged exposure to the non-fatal forms can cause permanent brain damage.
“Type O blood seems to be a mosquitoes' preferred blood type as compared to A, B and AB, but the only significant difference was when it was compared to Type A,” says Ulysses Wu, MD, Hartford HealthCare's chief epidemiologist and medical director of infectious disease.
Whilst “golden blood” is still part of the Rh system, it is the rarest known type. It is Rh-null: 61 Rh antigens are absent in it. If you're Rh negative, you still have some Rh proteins but you have more missing than you have present. If you're Rh-null, you have none of these antigens at all.
O positive red blood cells are not universally compatible to all types, but they are compatible to any red blood cells that are positive (A+, B+, O+, AB+). Over 80% of the population has a positive blood type and can receive O positive blood. That's another reason it's in such high demand.
