I'm definitely up for something a bit more original than good old fashioned vampires, though as long as they're not completely textbook or completely sparkly, they [i]would[/i] work well here. The idea of a Wendigo is more interesting on a moral and cultural level (though it really belongs to a different reasonable set of native beliefs). There's also the related Wechuge, which is slightly more geographically appropriate and may be worth checking out.

In general, I like the idea of the threat being something a bit insidious and of it potentially being able to disappear within the host or go back into hiding when all is said and done. On the one hand, it could lead to a sort of 'witch hunt' situation, but on the other, it gives people some hope and maybe makes them hesitate a bit before just blowing monsters to smithereens.