The most obvious less to me is the nature of good and evil. A person can try to be good, but be “infected” by evil, just as metaphorically a person becomes infected as a vampire. Then you live a cursed life, rather than a life of eternal bliss.
There are a number of interpretations we might make if we read the story thematically or symbolically.
I'd like to say that the Dracula story functions as a counter-part to our notions of idealized eternal life. What if we were granted our wish to live a human life forever, but we must become a monster in the process?
Taking this as the comment, we can see the story as an expression of the idea that human life is only "human" within its natural limits.