Cholera is a pretty vicious illness, and it seems to track disasters.

I'm no expert, but from what I've read, the actual cause of death in cholera cases is electrolyte imbalance. The bush cure IIRC is "a handful of sugar and a pinch of salt" mixed into sterilized water. The salt(s) are what they need to survive; but it can't pass through the intestinal wall without a bit of sugar. Something to do with the chemistry of osmosis (?).

Others here can comment with more authority.