Yssgaroth Taint
From Tardis Wiki, the free Doctor Who reference
The V Factor (PROSE: Vampire Science) or vampire virus (PROSE: All Flesh is Grass) was the distinguishing characteristics that "made vampires vampires".
The V Factor involved a gene that was added to the victim's biodata vampire conversion. The Eighth Doctor devised a method of purging a vampire of the V Factor. (PROSE: Vampire Science)
