>For a very long time now, I have been concerned and confused because I
>have heard so many conflicting stories regarding this subject.  I know
>that in dogs , you do not administer heartworm medication until a test has
>been done.  I'm told that if the dog has heartworm, then you do not give
>them the medication because of the larvae.  I'm told that this can kill
>them.  Is it the same in all animals, especially in ferrets?  Some say no
>and some say yes, so this is enough to confuse a person.  In otherwords
>should you begin heartworm prevention in a ferret and not worry about
>testing for heartworms?  In the past I also have been told that you don't
>see heartworms in ferrets real often.  What is your opinion on this?
 
Adult ferrets should always be tested prior to starting on heartworm
prevention, as should adult ferrets who have been off of heartworm
medication for a period of several months.  The prevention is actually
given to kill off larval heartworms during their immature period of growth
in the tissues of the body, before they become the large spaghetti-like
adults in the heart.  Thus, if a mosquito transfers the immature larvae
to your ferret, and the ferret is on the preventative, the larvae will be
killed before they ever have a chance to mature and set up shop in the
heart.
 
when there are adult worms in the heart, we have to be very careful.
Heartworm treatment (as opposed to prevention)is far more tricky.  You have
large worms living in the heart which must first be killed (the easy part),
and then broken down and absorbed by the body (the hard part).  If a ferret
is very active after treatment, the worms may fragment and be carried by
the blood to the lungs, where they may cause clotting (also known as
pulmonary embolism) and death.  The trick is that the body should hve time
to work on them in the heart, where they can be safely broken down and
removed.  Some small fragments always go the the lung, where they can be
safely removed - it's just when you have a massive shower of pieces of the
worm where you get into trouble with treatment.
 
Now when you just give prevention to any adult ferret you run the risk of
killing worms which you don't know about, and then setting up all the
parameters for a fatal embolism.  Thus, all adult ferrets should be tested
(preferably with the IDEXX SNAP occult heartworm test) before embarking
on any prevention program.  Young kits at 15-16 weeks, however, can start
directly on prevention, as even if they were infected by a mosquito shortly
after birth, the worms are still in the larval stages in the tissue, and
can be safely disposed of by the preventative.
 
No, we don't see a lot of heartworms in ferrets, luckily - probably as a
result of the fact that most ferrets live indoors, where the concentration
of mosquitoes is less (but not nil, so ferrets in heartworm endemic areas
should be on preventative).  However, undiagnosed cases of heartworms in
ferrets are often fatal, as the presence of even a small number of worms
can result in heart failure, as they interfere with the function of the
heart valves and over time, cause non-reversible heart damage.
 
Hopefully this has answered your question - but this is not a complete
treatise on heartworm prevention.  If you want to know more about
heartworms in ferrets, I have more information on heartworms on my site at
http://www.afip.org/ferrets
or you may visit Dr. Debra Kemmerer's section (who knows more about
heartworms in ferrets than anyone else out there on Mike Janke's
excellent medical site at
http://www.miamiferret.org/fhc/heartworm.htm
 
With kindest regards,
Bruce Williams, DVM
[Posted in FML issue 3230]