Anon, at 4 years of age you'd have seen heat before if she wasn't spayed,
but she could have a uterine stump which is being aggravated by estrogen
output from an adrenal growth.  We've been in that situation and her
symptoms were very like what you are seeing.  The way to know is
exploratory surgery.
 
My recollection from when we had ECE here was that it came on
gang-busters.  Some vomited before the horrible runs began but some
didn't and there just was no let-up of runs so bad that dangerous levels
of dehydration were a daily occurrence through part of it, calling for
approaches like sub-cu hydration or IV.  There was nothing on and off
about it.  Your ferret may be eating something which disagrees with the
ferret's belly every now and then.  If the runs become more common then
alternatives need to be investigated, but meanwhile think about what may
be causing gastric upset and rapid transit time.
 
ECE remains contagious for at least 8 months even though symptoms are
gone which is why it not unusual for people to wait a year before any
interactions which might expose any other ferrets.
 
Remember that ECE can permanently damage some ferrets' intestines and
that it is not unusual to have lasting things like IBD crop up secondary
to it.  If dehydration was too bad then kidney damage can also occur.
[Posted in FML issue 4071]