Even if your ferrets are never outdoors, you can bring in fleas or
their eggs on your shoes or clothing.

There's a whole FAQ dedicated to ridding your pet and your home of
fleas and ticks.  It's distributed in the usenet newsgroup rec.pets.
You can also get it by FTP:
<URL:ftp://rtfm.mit.edu/pub/usenet/news.answers/pets/fleas-ticks>
(that is, ftp to rtfm.mit.edu and get the indicated file)
or by sending email to
<mail-server@rtfm.mit.edu>
with the line
SEND usenet/news.answers/pets/fleas-ticks
in the body of the message (with an empty subject line).

In general, most products which are safe for use on kittens are safe
for ferrets.  Products containing pyrethins are okay, but don't use
anything containing organophosphates, carbamates, or petroleum
distillates.  Be especially careful with dips and sprays; shampoos are
much safer.  Follow the directions on the bottle carefully.

Dr. Bruce Williams, DVM, adds:

    You can use a premise spray around the cage, but often, the house
    requires bombing, too.  Get a bomb from your vet which contains
    methoprene (a flea growth regulator).  This will allow you to
    complete the job in just two applications - one to kill the adults
    and larva, the second two weeks later to get the ones that have
    hatched out since the first spray. (Make sure of course to remove
    your ferrets from the house at the time of the bombing...)  Fleas
    can be a real nuisance - before you bomb, make sure to wash all of
    their bedding and vacuum carefully so you only have to do it
    twice....

    Most insect foggers don't have a strong enough residual effect to
    hurt your ferrets. We routinely bomb our house for fleas and two
    hours later, the ferrets and dogs are romping through the house.
    (But I know that Siphotrol has a weak residual.)

    Signs of trouble - lack of appetitie, rumbling stomachs, diarrhea,
    vomiting, salivation, dilated pupils, stumbling.  You probably
    won't see them, but it's nice to know what to look for...

Long-term flea treatments

None of the three common long-term flea treatments -- Program,
Advantage, and Frontline -- have been tested on ferrets, so use them
at your own risk.  However, many people have been using them in
ferrets successfully for some time.  At least one vet prefers
Advantage because it's entirely external and never makes its way into
the ferret's bloodstream.

Program is used at the cat dosage per pound, administered monthly.
The medicine circulates in the blood and prevents fleas which have
bitten the ferret from laying viable eggs.  Therefore, every pet in
the house should be on Program to completely break the cycle; and you
may need to use this in combination with another product temporarily,
to kill most of the adults.  The pills can be crushed and mixed
with a treat or food, or the suspension can be put directly on the food.
Be sure that the right ferret gets the whole dose.  It should be taken
with a meal; in fact, the more food it's taken with, the more
effective it will be.  Have your vet call Ciba-Geigy at 800-637-0281
with questions.

Advantage comes in a tube.  It's applied once a month to the shoulder
blades, where the ferret can't easily lick it off (but other pets
could).  Ferret owners report that it works very well.  It's water
soluble, so you shouldn't bathe your pet except right before another
application, and the ferret must be completely dry before the next
dose.  The idea is to kill the fleas before they can lay their eggs,
and hopefully before they bite.

Frontline is also applied externally, and is also said to work very
well.  It's alcohol-based and smells a bit until it dries, but it's
also water resistant.  This means it may last longer than Advantage,
but if your ferret should happen to have a reaction to it (which I've
never heard of), getting it off could be more difficult.