Thankfully, I've only had to deal with fleas twice, once after bringing them home on myself, and once when I rescued a flea infested boy from a less-than-ideal situation. Thankfully in both instances, I was able to eradicate the fleas by following a few simple steps.
--note: I am not a vet. If you have questions about what treatments to use on your ferret, or your ferret is severely infested, please consult with your personal veterinarian--
What I do is wash the ferret in the tub.If you have multiple ferrets, wash them one at a time, keeping everyone in the bathroom.
Many people tout the use of Dawn dish soap but I've used regular shampoo with the same results. It's important to note that shampoo/Dawn will only kill the adult fleas on the ferret. It will not kill eggs, nor prevent fleas from returning. It works for a short-term situation-such as when I got home at 10pm at night with a flea infested ferret and had no Revolution on hand, but for long term prevention, medication will likely be needed.
Anyway, begin your standard bathing procedure and get your ferret nice and wet. Start lathering the soap at the neck so the fleas can't crawl up the head and escape. Let the soap sit a few minutes and then rinse well. If you'd like, add some conditioner/oatmeal rinse to soothe the skin. Leave the ferret to dry in the bathroom. (wash the towels once he's dry!)
While your ferret is drying, remove all bedding from the cage and wash well in hot water and regular detergent. If you think you have an infestation, then it may help to wash bedding that may have been stored near the cage as well. I also give the cage a good wipe down. I'm not sure this has any effect on fleas, but makes me feel better, and I'm sure the ferrets appreciate a nice clean cage!
You can also sprinkle Borax/salt/diatomaceous earth on the carpet and vacuum up to kill any eggs that may have been laid there.Repeat several times a week. There are pros and cons to each type of carpet sprinkling medium; I suggest researching the pros and cons of each and making an educated choice.
It may also be helpful to place a flea collar in your vacuum bag to prevent any eggs from hatching and re-infesting your house.
Flea powders may also be used, but use caution, as they are usually not safe if inhaled.
Once your ferret is completely dry, apply a flea treatment. I personally use Revolution which is off-label for ferrets, though it has been tested on them (see linky below)
I get a large cat dose of Revolution and split it between my 3. You vet may be able to advise how to do this.
Advantage Multi is one that is actually approved for ferrets, though I have not used it myself.
Advantage kitten and Frontline have also been used (off-label) by ferret owners, but I'd personally go with Revolution or Adv. Multi first. Percy had a slight reaction to Advantage; he got a red itchy spot where it was applied, so I don't use it any more.
Avoid products made for dogs, as these usually are not safe for ferrets. I will note that Revolution for dogs is the same formula, so splitting of a large dose may be feasible. Again, your vet may be able to advise you how to do this.
One thing I can't stress enough is to avoid cheap brands like BioSpot, Sargents, and Hartz. At best they are ineffective, at worse, your pet could have a serious reaction. There are some seriously scary videos out there of pets having devastating reactions to these types of meds. Even though they are cheap, avoid them at all costs.
I occasionally also see "natural" remedies such as garlic, vinegar, or essential oils touted as flea repellents. While I have not personally tested these methods, here are a few things to consider:
-fleas have no mechanism for scent, so they are not repelled by strong smells
-garlic has been known to cause anemia in pets. There is no safe threshold when feeding alliums; the tolerance level may vary by pet, and size is not an indicator of tolerance.
-vinegar can be irritating to open skin and may be drying
-essential oils can be irritating to a ferret's respiratory system and there is some evidence to suggest that the phenols contained in some oils may build up in the system over time, causing toxicity. If you choose to use EOs on or around pets, please consult with a certified aromatherapist (note: someone who sells EOs may very well NOT be a certified aromatherapist.)
It's important to note that whatever method you choose, in the case of severe infestation, you may have to treat for several months before the infestation is eradicated. If you have other animals in the house, treat them as well, so they are not acting as a happy host the fleas can transfer to.