This is actually something I wrote for someone on the FHL, but it can
answer questions that a couple of folks on the FML posed, too.
 
       -----
Well, first off they are not known to get the rhinoviruses that we call
human colds, though they can catch influenza (which may seem like a cold
if a human has only a mild case), and we have had a bacterial sinus
infection in the household years ago that they turned out to be able to
get.
 
Such infections are not caused by being exposed to the cold; they are from
exposure to the infectious organism which causes the disease, so isolation
during contagious times, many hand washings, facial masks, etc. can be
useful in stopping the spread.
 
Ferrets actually do well in the cold, and I sure that many a British
ferret keeper will tell you of their ferrets out in the winter.  They
actually have more of a problem with too much heat.
 
There are special types of heating pads made for animal use or for being
able to be covered.  Using standard ones for those uses can at times
result in a fire.  I am sure that is something you would rather avoid.  I
can well recall the day a friend who is a fireman dropped by to relax and
told us of a fire that day in which a person had tried to use a standard
heating pad to heat seedlings and instead wound up burning down the house
 -- total loss.
 
If you are worried then give them extra blankets. They will use the
ones they want and toss off the rest.
[Posted in FML issue 3631]