What counts as a disease?

Do any books contain a rules definition of what is and is not a disease.

Here are some examples of aliments I, the DM, would like to see if they match the definition if such a thing exists. I put a broad range of aliments here and included things like Kidney Failure to try to illustrate what I would like to compare to the definition.


  • Down Syndrome
  • Diabetes
  • Kidney Failure
  • Malaria (Dormant or Active)