I'm no expert on it but I wouldn't want them in my discus...
http://digitalcommons.unl.edu/cgi/vi...text=usfwspubs
indicates its probable that any species of fish can be infected.
This pathogen is usually free living but can switch modes to parasitic depending on its environment and needs.. Not something I would take a chance on. I would think Metronidazole would work on it.
hth,
al