New diagnosis of mites

Hi all
My bunny has just been spayed and when I picked her up the vet noted that she had some fur mites.
She went for her check up a month ago and didn’t have any then, and since then hasn’t been in contact with any other animals other than my other rabbit (nothing was detected on him either).
Does anyone know how rabbits are able to pick up fur mites when they don’t meet any other animals? Just want to make sure they don’t get them again!
Thanks
Note from Rabbitmatters:Unfortunately mites can sometimes be inherited from the mother and may well re-occur from time to time, without any contact from other animals