The Desmodus bloodline came from a human 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.
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Desmodus is the purest, strongest bloodline of the five bloodlines. Desmodus vampires are strong, fast, and they have a special ability the other vampire bloodlines don't have: they can see perfectly in the dark. This bloodline is so rare that only Valemont the vampire (believed to be deceased, but that may not be the case), Eric Gracen (now deceased), and Maggie Gracen are known Desmodus vampires.