Vampires have a long story in european folklore, and their myth probably have benefit from numerous sources.
However, a couple of months ago I was watching an old horror movie and I suddenly wondered if the legend of vampirism might have developed from the real disease of rabid (spelling?).
At least some (but definitely not nearly close to being all) of the D&D vampire's traits may have something to do with symptoms of a rabid person, can some physician around comment about them? I am trying to make the following up, because I have no real knowledge on the disease:
- rabid disease is transmitted via bite = someone drained by a vampire becomes a vampire himself
- rabid disease is (among others) transmitted by dogs/wolves, bats, rats = affinity/shape to this kind of creatures
- one symptom is intolerance to strong light and strong odors = weaknesses against sunlight and garlic
- one symptom maybe hydrophobia? = that would explain the running water legend
- general behaviour of a rabid could be quite uncontrolled (rage?) = perhaps could explain exceptional strength and endurance
Add in some religious elements (impossibility to cure a disease may lead public opinion to add some supernatural to it) like "the cross is the only defense", or that the vampire is actually evil/possessed/dead, and popular phobia of plague spreading can do a lot to improve the legend.
These are just some thoughts I had a couple of months ago, completely unsupported by any source or medical knowledge, so don't take them seriously
