A credible related theory- most supernatural creatures are immune/resistant to disease. A sign of supernatural power... or a sign that disease is humanity's bane?

To answer the question, some theories:
  • The godmachine/exarchs/both did it, ensuring supernaturals have reason not to just rule the world in broad daylight.
  • Vampires were, seemingly, created by a curse- so were all the rest, and the banes remind them that they are not meant to be gods.
  • It all comes from arcadia and runs on story logic, and what good is a story with an invincible character?,
  • The underworld infests