From the writings of Guniya Cress
There are no records of vampires before the Terror of Belzaor. My own investigations into their nature and origins, applied to hundreds of years of archival records, suggests it is some kind of parasitic spirit, another kind of specter or demon, from whence Belzaor emerged.
They are not unreasoning or intrinsically hostile monsters, however. Consider the actress Luminara Ombre, living openly as a vampire has given her a certain notoriety. One cannot deny she is extremely skilled in the performing arts and, by all accounts, she drains life energy only from those willing and never fatally.
Vampires, specters, curses and blighted creatures.. Belzaor must be destroyed, somehow. It must be possible.