Leigh,
Otitis externa and interna refer to inflammation of the ear canal, internal
and external, as you thought.  But one thing I'd like to add to that is
inflammation isn't always just irritation, it can be an infection, as well.
Infection of the ear canal can cause hearing impairment and pain, but when
you consider how close the inner canal is to the brain, it's a very scary
thought.  There is a type of infection in human ears that is so bad it's
considered malignant (easily spreading and doing damage) to the brain.
I'm not positive, but I believe I've read that a case of ear mites left
untreated in animals can get this severe.  They are not always easy to
diagnose, either, so if you suspect that your animal has been exposed, or
have reason to believe mites may be in residence, take your ferret to the
vet.  At the least you can save the ferret some irritation, at the most,
their very quality of life.
 
Ataxic means unable to control motions, making random, unintentional
movements.
 
Thank you for sharing the information about Advantage and Frontline being
effective with ear mites, as well.  I had no idea that was the case.
 
Sherry
[Posted in FML issue 2570]