So, so many.
Cholera comes to mind (bacterial)
CJD (prion)
Various forms of mass hysteria (psychological)
Then there are weird edge cases like Rheumatoid Arthritis: epidemology and paleontology looks /exactly/ like a pathogen (inducing an autoimmune response to the tissues it hides among) except we've looked, a lot, and no microcritter has been convicted yet.
Yeah the psychological is interesting.. and autoimmune, right. I wasn't really thinking a disease like diabetes which is caused by lifestyle. I was thinking germs. The bacterias make sense, but I don't know if they have been pandemic scale. But I guess basically over the last century the population increase makes "pandemics" possible whereas before not so much maybe... But in that time I don't think there has been a national-level bacterial contagen. Maybe because that easier to fight with antibiotics and containment.
Koch's own work shows that Cholera was not caused by the bacteria supposedly responsible
He drank a beaker full of vibrio cholerae and didn't develop cholera disease
