Ringworm -------- Ringworm (a fungal disease of the skin similar to athlete's foot) has been reported in young ferrets and may be transmitted by infected cats. As a rule of thumb, products manufactured and intended for use in and on cats (dewormers, flea products, ringworm medications, etc.) are safe and suitable for use in and on ferrets, with one exception: flea collars should never be used on ferrets.