Fleas are nasty because ferrets are so low to the ground they just become natural flea picker-uppers. Vacuum every other day and use flea powder the first time to suck up and kill the fleas IN the vacuum cleaner. Do NOT use flea control collars on ferrets. Remove as much carpeting from the ferret play area as possible. Fleas love to hide in carpet, furniture, etc.
Soap kills fleas.
If you must use a product to ward off fleas, Advantage or Frontline, available from vets, is effective on ferrets - use the kitten dose. Ferrets are susceptible to usually three different types of cancer, and sometimes get two of the kinds at the same time. Lymphosarcoma - juvenile lympho usually strikes before two years and kills very quickly. Adult usually strikes at 5 years and up and depending on the aggressiveness of the cancer and the options of the owner and vet, can be controlled and even sent into remission. Suspected to be hereditary.