If you join http://groups.yahoo.com/group/Ferret-Health-list you can ask your question there. It has a number of excellent ferret vets, a ferret veterinary pathologist, and other experts so just pose your question. In our home (20 years with ferrets in the family come June) I can not recall any ferret getting a strain a second time around. I have seen people give ferrets influenza and ferrets give people influenza, and I have seen that happen with a sinus infection which DID trade back and forth multiple times in the same individuals. [Posted in FML issue 3689]