Remember that probabilities are low, but the disease is so devastating
that it makes sense to use more precautions -- a similar situation to
preventing rabies.
 
I got searching under topics like FERRETS + "Mad Cow Disease" and found:
http://www.ehso.com/ehshome/madcowdisease.htm
(In Britain, though, I would expect that those who had been around wild
polecats would have also been around, handling, or eating some game;
you'll see in there why I mention that.)  It's an interesting read from
Georgia which includes:
 
>Cattle remains in animal feed in the U.K. have also spread
>encephalopathic diseases to domestic cats, captive wild cats
>(puma, cheetah, ocelot)...
 
but that doesn't say whether ferrets could get it, or if they live
long enough to do so, and if they do get prion caused spongiform
encephalopathy that doesn't mean that they don't get a different type so
may not get the ungulate form.
 
www.pcrm.org/health/PDFs/pv_madcow.pdf
 
http://www.findarticles.com/cf_dls/m0FSL/2_70/55525527/p2/article.jhtml?
 
>The six animal TSEs and the animals in which those diseases occur
>are listed in Table 1.  Animals are used in the research of TSEs,
>especially CJD.
>
>Experimentally, the causative agent for CJD has been isolated from or
>transmitted to many animals.  These animals include monkeys and other
>primates, mice and other rodents, sheep, goats, deer, calves, minks,
>ferrets, cats, raccoons, skunks, and rabbits.(18)  Animal
>experimentation is used to determine sterilization and decontamination
>guidelines, establish a definite diagnosis, and research the unknown
>factors of the disease...
>
>Scrapie                             Sheep and goat
>Feline spongiform encephalopathy    Cat
>Transmissible mink encephalopathy   Mink
>Bovine spongiform encephalopathy    Cattle
>Chronic wasting disease             Elk and deer
>Exotic ungulate encephalopathy      Ungulates (ie, having hoofs)...
 
I think I should read that one in detail when time allows.
 
http://www.mad-cow.org/~tom/Marsh.html
 
Cattle can apparently get mink encephalopathy, but I don't know if the
other is true:
>Cattle are susceptible to experimental infection with the Stetsonville
>isolate of the transmissible mink encephalopathy (TME) agent.
 
 
http://www.mad-cow.org/99feb_cwd_special.html
(The deer and elk version in "Host range of CWD is altered on passage in
ferrets"  (Virology 1998 Nov 25;251(2):297-301) whihc can be read at
http://mad-cow.org/~tom/dec98_mid_sci_news.html#hhh
 
>investigated the use of ferrets (Mustela putorius furo) as a small
animal model of CWD.  The inoculation of CWD into ferrets resulted in
an incubation period of 17-21 months on primary passage that shortened
to 5 months by the third ferret passage... The brain tissue of animals
inoculated with ferret-passaged CWD exhibited spongiform degeneration
and reactive astrocytosis.
 
Note that laboratory infected animals used for research will have an
extreme exposure such as direct innoculation.
 
BTW, there is evidence that replicating folded proteins may be involved
in long term memory.  It would be interesting if long term memory began
as an infection.  It's easy to see the genetic advantage to both parties
of such a symbiosis.
 
http://www.nytimes.com/2003/12/25/science/25MEMO.html?
ex=1387688400&en=12fdd4613d3e2a59&ei=5007&partner=USERLAND
[Posted in FML issue 4375]