The wanton dead. Their flesh moves only to fulfill their selfish desires. A Vampire is a hideous creature, draining the life of those around them.
A Vampire tends to keep at least one Thrall among those that they take from. This Thrall is the enabler. The one person who feeds the Vampires belief that their actions are OK.
Just being in the presence of most Vampires, you could never tell what they are. Generally, they are charismatic and oft times a pleasant person socially. The problem comes behind the scenes, they live off of others by any means.
Under a guise of sweet words and good intentions, the Vampire will lead on those around them gaining free living and a free place to feed. Their good nature makes them hard to turn away and their Thrall will defend them.
How do you eliminate the Vampire's nature? This is the hardest part of the situation. You cannot let them continue what they are doing. Yet, is it worth it to cast them out and lose the friendship with their Thrall?
Yes. Being a good person is of utmost importance, but standing up for yourself to the leeches on society is more important. You can do nothing to improve life for yourself or others if your life is not where it should be.
Are you outside of a group with a Vampire in it? You can try two things. Confront the Vampire privately or talk with your friends why they let it happen. This circumstance is difficult to handle, but with respect and tact you can gain insight into the situation. The most important thing to remember about it... If it doesn't effect you, don't get involved.
Do not let yourself fall prey to the wiles of those that would use you. The cycles of life will bring people in and out of your world regularly, you never need to support someone at the expense of the self.
Support your students, those that will learn from you, grow from you, and when the learning ends, it is time to part ways. Do not force the relationship to linger, nor let them hold on like a nursing child. When the end comes, let it go and make it end, lest you end up having a Vampire take roost in your home... or worse, you fall to becoming one yourself.