If you comb through the ferret hair, you can usually see fleas if they are
there.
 
We are fostering an adrenal ferret, and he was always scratching, and we
thought it was dry skin since he is bald.  It turned out to be ear mites.
Even though the mites are in the ears, he kept scratching his back and
sides, and getting red marks there--which is why we didn't think ear mites
right away.  So, I'd suggest you check the ears.  If they are unusually
dark and waxy, chances are that you have them.
[Posted in FML issue 3378]