There was a question about giardia...
 
There are lots of listings on the Web under the search terms "giardia AND
pet"--too many to list here, but here are a few
 
One about dogs, but still informative:
http://www.flatcoat.com/giardia.htm
 
and another on internal parasites including giardia:
http://www.nsvh.com/internal_parasites.htm
 
and one about its origins and effect on humans:
http://vm.cfsan.fda.gov/~mow/chap22.html
 
Giardia is a protozoan and it is tough to kill.  The medicine your ferret
got for it, Flagyl, is the same thing humans are given.
 
Giardia has become a problem in the 'pure' mountain streams of the
Rockies--I live in the mountains and know a lot of folks who've gotten
giardia while hiking and camping-- but it is fairly common everywhere.
Some people say it came from beavers.  I think, but I don't know, that dogs
can get infected with it but not have too many symptoms, so I would not be
surprised if it could be spread via the family pup to the family ferts.
[Posted in FML issue 2587]