The Serpentes bloodline came from a snake who contracted vampirism by the original vampiric infected bat.
There are five vampire bloodlines from five different species who contracted vampirism by an infected bat centuries ago. The five bloodlines are Panthera the panther, Serpentes the snake, Desmodus the bat, Crocodilia the crocodile, and Aotidae the monkey. These five vampire bloodlines make up the Houses of Valemont University, tho Desmodus House burnt down years ago and since there were no known Desmodus vampires left, it was not rebuilt.
-Spoilers Alert- Edit
Beatrice Granville is a member of the Serpentes House on campus.