The high globulin and the GI signs made me think about AD also.  Since you
do have some AD positive ferrets in the house and 1 in the same cage, I
would recommend doing a CEP test thru United Vaccines.  A second option
is to do an electrophoresis to see what % gammaglobulins this one has.
 
As for having the "non-active variety" of AD, I do not think that can be
said.  So far only 1 strain of ferret AD has been found!  I do not know
why some appear to have the virus with no clinical signs and others have
mild to fatal signs.  At this time we do not even know the exact modes of
transmission of AD in ferrets.  You have been lucky that the positive one
has not shed the virus and exposed your other ferrets.
 
If the CEP comes back positive, then I would use pediapred to help control
the immune complexes and GI signs.
 
Hope that helps,
Jerry Murray, DVM
[Posted in FML issue 3427]