Most people who react to ferrets apparently are reacting to whole males.
Adrenal neoplasia can simulate being whole because of the hormonal
production.  (General note for anyone: Surgery should cure that.  If
surgery isn't possible for health reasons look into the medication
combinations advised by Dr. Jerry Murray (Search under AFERRETVET in
the "from" box, and ADRENAL for subject in http://fhl.sonic-weasel.org
because they can block hormonal cascades if it is hyperplasia which is
the most common adrenal growth.))  Hopefully, your allergies are not
generalizing.
 
BTW, if this happens with more than one ferret have you considered that
you might be allergic to something the ferrets are eating instead of the
ferrets themselves?  This happens with humans, too.  It's funny because
it is only in recent years that it has formally been announced that if
someone with a severe allergy has been kissed by someone who has eaten
the allergen that an allergic reaction can take place, but families with
folks in them who have severe allergies have known this from experience
for ages and ages...
 
Desiree, I think that all of your questions as well as way more are
answered in past posts of Dr. Jerry Murray.  See above in the first
paragraph for how to find these posts.
 
Treating for parasites safely:
There is LOTS in the FML Archives at
http://listserv.cuny.edu/archives/ferret-search.html
A compilation can be found at:
http://www.smartgroups.com/vault/ferrethealth/common_parasites.txt
with later info in
http://fhl.sonic-weasel.org
I think there might be a vet answer in one of those for you, but not
sure.
[Posted in FML issue 4392]