D&D 5E Give me your best diseases!

[Wepwawet]

In my Curse of Strahd game one character got blessed by Mother Night.
One of the effects is a blood thirst surge when in melee combat:

After doing a melee attack she must make a DC 13 Charisma save, if she fails she must use her bonus action to bite the target of her attack. She has proficiency with the attack and it deals 1d4 damage.

That could be an interesting disease (Bloodlust Fever? Rabies?). Of course now she learned to do her bonus actions first, but occasionally forgets.

 

[Nebulous]

A disease that removes the darkvision ability.

Now that I would like to see.

 

[lowkey13]

*Deleted by user*

 

[CapnZapp]

Got a friend running a game in a pestilent land and she asked me for the worst diseases to fill the place with. I've got the ones in the 5e books and a few of my own, but what are your best homebrew diseases?

Anything that can't be trivially fixed with Lesser restoration or Paladin Lay on Hands, to be honest.