Cage trapped beasts don't spread contaminants unless the cage gets covered before it's captured.
Thanks for the tip! I'll go snatch the thing then.
What symptoms does it have? Perhaps it's useful as a bolt poisoner?
Symptoms? No idea. It's already killed a troll, a whole herd of Draltha and another FB just by walking next to them though. They get the flashing green x that dwarves get when their guts get caught, but there's never any vomit lying around. I'll catch the thing later, and post back here to let you know.
How do you go about poisoning bolts? Also, can you poison other weapons like spears? I've never heard of that done before.
Hrm...
Perhaps you could do this:
B-|=a
Where B is the beast, - is a gap, | is a raised drawbridge, = is a retracting drawbridge (where you put the bolts).
You drop the bolts in from above, then lower the drawbridge. The beast proceeds to spew syndrome everywhere (since it spews syndrome everywhere regardless). Then, you pull the floor out to collect the bolts.
Only problem is that this might break the bolt stack. And if the noxious secretion isn't some form of dust (say it's a gas) then this is pointless.
Alternatively, you could just make a bunker by the entrance. The beast will spew is secretions regardless, so you could lower a bridge (in front of fortifications) to poison entire sieges as they path through. A different, civilian entrance might be desireable though if the syndrome spreads...