My first fortress on the 31.01 release had a very interesting encounter with a FB. I had walled myself off from the caverns, and after several dozen FB's came, eventually one came that excreted some sort of poison whenever it went through water, turning it white. Eventually I needed a source of freshwater, and since I was on the ocean, I had to use cavern water for a water source. After a while I noticed I was getting a lot of messages about job cancellation, resting injury. Apparently the water had been contaminated with a paralytic, and anyone who drank from it became numb, temporarily.
And my dwarves became immune to pain.
Ooh, more info, please? I'm syndrome-obsessed, and I don't know where or how what you described would work in the current system...
If you care about my syndrome: it was spread by forgotten beast blood, which you obviously get in spades. Immediate symptoms were skin blistering (usually on the feet, since it was being tracked around, but full-body for the unlucky champions who killed it), which eventually spread to fat, muscle, and bone, causing extreme pain. Within several days the blistering developed into full scale necrosis necessitating surgery to correct, and leaving massive scarring. I'm unsure if this was a bug, but on several occasions necrosis developed without any signs on the 'wound' screen, only visible through the z-menu. When treatment was impossible or insufficient, dwarves perished due to infection within a few weeks, although several became paralyzed and suffocated within *literally* one to two days of exposure. It would have been quite cool, if it weren't totally uncounterable.