Part of this will help Patty with all content being for FML members.

Raisins and Grapes are most documented causing this in dogs and cats
but toxicity in ferrets from grapes and raisins also has been reported.
The number may need to be large (7 or more) for most ferrets but
ferrets stash treats so large numbers eaten at once can occur. If
health is compromised or perhaps if the individual has a genetic
vulnerability then it may happen for fewer pieces of fruit.

An excellent veterinary article on this was in Ferrets magazine in the
past. I hope that it becomes available online some time.

Multiple possible reasons that this happens have been studied but as
far as I know the actual cause MIGHT unfound though there is an
interesting article I can not access. It looks like sultanas (yellow
raisins) and currents ALSO cause the problem. The article is Vet Rec.
2009 Apr 4;164(14):430-1.
Factors influencing outcome of Vitis vinifera (grapes, raisins,
currants and sultanas) intoxication in dogs.
Sutton NM, Bates N, Campbell A.
Veterinary Poisons Information Service (London), Medical Toxicology
Unit, Avonley Road, New Cross, London SE14 5ER.

PMID: 19346542

Speaking of nephrotoxicity, there are some interesting threads going on
right now in the FHL on possible causes like zinc poisoning from some
types of cage wire or galvanized dishes or from cadmium, and a list
member has posted that her vet has found the zinc toxicity can cause
the onset of reversible diabetes in ferrets (once the ferrets are
treated also to remove the excess zinc and the cause of poisoning is
removed).

Something else new: The Michigan State Ferret Health group has found
ferret Tyzzer's Disease. That has not been published yet but mention
was in the Veterinary School Publication, "Perspectives", so I asked.

Sukie (not a vet)

Recommended ferret health links:
http://pets.groups.yahoo.com/group/ferrethealth/
http://ferrethealth.org/archive/
http://www.afip.org/ferrets/index.html
http://www.miamiferret.org/
http://www.ferrethealth.msu.edu/
http://www.ferretcongress.org/
http://www.trifl.org/index.shtml
http://homepage.mac.com/sukie/sukiesferretlinks.html

[Posted in FML 6366]