Every vampire knows the stories of the Taint. It is the sweetest blood and addictive. However, no one has drunk it for centuries. The secret of it was hidden, on a remote Greek island, by some Monks. It increases the urge to feed over any other single impulse. It stops vampires from thinking rationally. It intoxicates them, draws them in like a siren, and makes them quite inefficient at hunting.
It is a virus in the human blood, which is caused by a bite of a very rare spider. It is like bloodpoisoning. The human who is infected by this can die of it. All of the vampires will run after the human because of the sweet smell of the blood. When they smell it they can't controll themselfs anymore. All they can think of is feeding.