Dear Anonymous (name withheld)-
 
>I'd like to know why you recommend pretreatment for all CDV vaccinations
>in ferrets.  Particularly, what convinces you that pretreatment w/
>histamine blockers doesn't substantially affect immune response, and that
>DVMs will know not to pretreat w/ steroids?
 
The reason I now am tending to recommending pre-treatment for all ferrets
with anti-histamines is for a number of reasons -
 
1) there is absolutely no way these days to predict who is going to react
and who is not.  A history of no reactions does not guarantee that the
next vaccine won't be the one to cause a reaction.  While it is extremely
unlikely that a kit experiencing its first vaccination will react, as it
has never been exposed to the offending antigen before, the chance
increases every time a vaccine is given.
 
2) Antihistamines are cheap, readily available, and have no long-term
complications.  The margin of safety is also extremely high.
 
3) Not to belittle the intelligence or memory of veterinarians and owners,
but I strongly feel that if it becomes the "rule" of vaccination for CDV in
ferrets that if you pretreat with antihistamine, then it will most likely
get done.  If it continues to be the exception, then reactors will slip
through, and ferrets will die.  Unfortunately, we may never know how many
ferrets are helped by pretreatment - by the theory behind this practice is
sound, so I will continue to advocate that all ferrets are pretreated.  If
someone decides that it is not warranted, and ferrets react, then that will
be on their head.
 
Antihistamines do not affect the animal's appropriate reaction to the
vaccine.  What they do is block the histamine receptors on mast cells for
a short period of time, preventing the aberrant component in the vaccine,
which causes the reaction, from binding to the mast cells and starting
the anaphylaxis cascade.  This immediate reaction has no bearing on the
long-term reaction to the vaccine, and is only a nasty and life-threatening
complication - mast cell degranulation has no useful purpose in
vaccination!
 
The problem with steroids is that it diminishes the body's ability to
react immunologically in a number of ways.  It decreases the ability for
lymphocytes (the main cell type involved in the processing of vaccines and
antigenic memory) to migrate out of the lymph nodes and blood vessels to
the site of vaccine injection, or into the draining lymph nodes where the
vaccine antigen is processed.  It also reduces lymphocyte proliferation,
and in higher doses, results in actual death of lymphocytes within nodes
and lymphoid organs (lytmphocytolysis.) Antihistamines have no effect on
the lymphoid organs or the cells within them - they simply block histamine
receptors on mast cells - a cell that really does not participate in the
bodies long-term response to vaccines.
 
How can I be sure that vets don't use steroids as part of the pretreatment -
I can't.  All I can do is stress pretreatment with antihistamines ONLY,
and hope that the vets understand the recommendation and why it is given.
I also can't prevent vets from using injectable anesthesia, or doing
abdominal surgery without appropriate fluid therapy and watchfulness for
hypothermia, but I do attempt to educate on these points whenever the
opportunity presents itself.
 
With kindest regards,
Bruce Williams, DVM
[Posted in FML issue 3247]