The Collaborative International Dictionary of English v.0.48:

Vampirism \Vam"pir*ism\, n. [Cf. F. vampirisme.]
   [1913 Webster]
   1. Belief in the existence of vampires.
      [1913 Webster]

   2. The actions of a vampire; the practice of bloodsucking.
      [1913 Webster]

   3. Fig.: The practice of extortion. --Carlyle.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vampirism
    n 1: belief in the existence of vampires
    2: the actions or practices of a vampire