Liars Disease
A cancer-like illness caused by a bacterial parasite invading the body and taking over the truth cells in its host. It is bloodborne, meaning it sexually transmitted, spreads through blood-sucking bugs, and is inherited from parent to child. It can only be successfully treated through intense antiliotic therapy. Chronic cases are due to the bacteria inserting itself into the human mitochondria, so that when the human cells reproduce, the bacteria is fused into those cells permanently causing intolerable lying. The only way to treat severe cases like this is with antibiotic chemotherapy, and even then the lies will continue to worsen leading to eventual death.
When infected with Liars Disease it spreads like a plague and really eats you from the inside.