WMG / Planet Terror

The Planet Terror Virus is Mutated Culebra venom

But they didn't get the "mix" right, it was intended as a super-soldier serum, turning their soldiers into powerful vampires, they didn't realise that you need a living Vampire to inject it, being that the vampires in both the movie and TV series of From Dusk Till Dawn the vampires are psychically linked, without the "Sire" the people infected with the virus turn into just bloodthirsty ghouls.