This idea... is incredible. Or, at the very least, has incredible implications. I think it's exactly the kind of thing that poisons and diseases should do.
Other ideas for fungal parasites:
* One that causes nerve damage (this may or may not also cause insanity).
* One that (eventually) causes berserk, melancholy, or insanity, like a failed strange mood. Tripping out is different for everyone, so this could be a single parasite, or several different ones.
* One that causes limbs to wither, like they grow mushrooms that feed on the limb they're attached to. ... Actually, it would make more sense if they slowly spread across the dwarf's whole body, eating limbs as they go and making for a very unsightly Dwarf. The description block would be great for this.
* One that causes attributes to wither.
* One that changes personalities, or preferences.
* One that simply causes unhappy thoughts (like a fungal parasite version of the common cold. I guess this is more like a disease than a parasite, but the two topics seem similar enough).
* One that alters the digestive tract, leading to... actually, without putting poop in the game (which Toady seems against, for good reason), I'm not sure how we could handle this except for unhappy thoughts.
Other parasites would be great, too. Like fleas. Imagine a whole zoo full of elephants and giant leopards getting fleas, and spreading them to all visiting Dwarves. Cats spread fleas by the thousands. Misery ensues as your entire fortress is forced to take flea baths in carp-infested waters. Oh, yes. Fun will be had by all.
Ideas for dealing with this:
* Getting rid of your Infected Plump Helmet problem would actually be kind of easy. Stocks->Plants->Plump Helmets->Dump. Making sure your entire farming population were clear of the disease? Not so simple. How does a diagnosis work if there are no immediate symptoms? Hmmm...
* Any disease that is not incredibly terrifying should probably have a decent period of symptoms before something crazy happens, giving our future hospitals a really good reason to be there (as if injured soldiers, woodcutters, and fisherdwarves weren't reason enough).
... Okay, so I don't have a lot of ideas for this end of it. c.c