Replacing vampires

A little bit off the "vamp" path, but if you read Stephen King's "Wolves of the Calla", you'd know about a group of supposed "vampires" that forcefully take children from their villages to their den. After some weeks have passed, they come back as giant half-wits (basically, lobotomised) and become a burden to their parents and caretakers.

What I mean is that your "Renfields" don't have to be eternal blood-thirsty servants or zombies, they can just be "consumed" once and left hollowed and empty, like a bag of bones.