I have a ferret and my father raised ferrets on and off over the years. I think I have heard of the disease your talking about but not familiar with it off hand. What are the symptoms? That may give a clue as to the cause or the right diagnoses. It could be an environmental change is needed to fix the issue.
Recently, I found out that Ferrets are the only animal that can actually catch colds from humans! My ferret had a cold and I got one after handling it. The good news is there are over the counter medications for cold symptoms in ferrets available.
By the way, have you had any problems with fleas with your ferret? I can't get mine to STOP getting fleas. I've given her flea baths and spray almost weekly. They go away for a day and come back. They hide at her ears and nose! I am worried about some of the flea medications are too strong. Any suggestions? Thanks!