Vampire Blood Transfusion

I recently watched this movie called "Dark Shadows" which features Johnny Depp and,  always, along with Helena Bonham Carter. It was a really good film if I may say so myself - the humor and weirdness really added up to the awesomeness of the movie.

There was a part of the movie where Dr. Hoffman, played by Bonham Carter, was stealing blood from Barnabas Collins, a vampire played by Depp, to obtain eternal youth and be beautiful forever through blood transfusion. When Barnabas found out about this trickery, he immediately bit Dr. Hoffman's neck and then she died. At the end of the movie, it was shown that Dr. Hoffman herself became a vampire.

Now, I was wondering how the process of becoming a vampire takes place. Well, the most popular would be by being bitten on the neck by a vampire. Apparently, it was shown in the movie, though by no means of confirmation, that transfusing vampire's blood to your own gradually makes you one - at least hinted by Dr. Hoffman in the movie.

I'm also left in wonder about the idea on how being bitten by a vampire makes you one. Do the fangs of these vampires have venoms or anything of some sort that allows the prey to succumb to being a blood-sucking immortal? I wonder.