From Lost Fables Wiki
Spread through blood contact with undead.
Any undead, aside from sentient ones, or infected person can spread the virus, typically through bites or fluid transfer, though Ghosts created through necromantic Truths or by Covrudurth himself as opposed to naturally occuring can also cause the disease to spontaneously mutate in those who they touch.
All but Drachev may contract the Gift
Only minutes after contact with the virus, the body begins to respond, breaking out in chills, accompanied by body aches, and a couple days after a runny nose and sneezing will develop. Generally speaking, for the majority of people, this is as far as it goes, an unpleasant experience which lasts for a couple of months, but for those who understand and have used Truths, the illness spirals downward. Firstly, the symptoms never stabilize, the body aches and runny nose steadily grow worse, eventually spreading into a cough and then pneumonia. The chills spiral into core temperature cooling, and, coupled with the pneumonia, this can prove deadly. About six weeks into this process, the caster will begin to hear the voice of Covrudurth or one of his False Dragons in their mind, promising them relief from the illness and life eternal should they pledge their spirit to him. If they do, their soul is yanked from their body, immediately becoming a ghost shackled to the will of The Bitter Cold. Sometimes they find themselves recreated into Dauridar through this, but most frequently, they are simply left to their own devices, to wander the material plane eternally, without any ability to resolve their condition.
For a non-Truthsayer, it is non-deadly, while for a Truthsayer, it is always deadly without careful management of the symptoms
The only cures are magical panaceas, or to let the virus run its course. With careful symptom management, only 80% of Truthsayers will perish to the virus.