You do not say how your ferrets are being treated, with what medication. James Fox's Biology and Diseases of the Ferret 2nd E. p.387 suggest dipping in a 0.0125 Amitraz suspension several times over some lengthy time with the same medication as ear drops and extra strength tail dips, followed by more higher strength dips for whole body again.with eventual complete cure. I will give the full treatment schedule if you need more details. Tony (not a vet), Sugar and Suki. In memory of Sally and Sue. [Posted in FML 5751]