Heartworm disease in the domestic ferret is a significantly
under-recognized problem. Many veterinarians do not know
enough about the ferret to understand that ferrets are susceptible
to Dirofiaria immitis.
Clinical signs are similar to those in the dog, but often
progress much more rapidly, so early diagnosis is extremely
important. Clinical signs include dyspnea (trouble breathing),
tachypnea (rapid breathing), anorexia, pulmonary rales (harsh
lung sounds), holosystolic heart murmur, ascites (fluid
in the abdomen), coughing, fluid in the thoracic cavity,
and sometimes sudden death. Many cases of "unexplained"
sudden death in ferrets are heartworm-related.
Diagnosis is made readily with the IDEXX Snap heartworm
antigen test. I have used the IDEXX test for about thirteen
years and it has proved to be extremely useful. Ultrasound
has actually been less accurate in that it has produced
both false negatives and false positives. There have been
two cases of heartworms diagnosed by experienced ultrasonographers
where no heartworms were found on antigen tests or necropsies.
Conversely, two cases of heartworms diagnosed by antigen
test and confirmed on necropsy were not seen by ultrasound.
It is possible that the presence of only one worm accounted
Until recently, treatment has been marginally successful.
Both Caparsolate and Immiticide have been used and survival
rates with both treatments have been disappointing. Ferrets
are at high risk of sudden death from worm emboli. Immiticide
has not been superior to Caparsolate in this regard. In
fact, judging from my early experience, Immiticide survival
may be lower, although the ability to administer the drug
via intramuscular injection makes it a more attractive option
for veterinarians who are not experienced working with ferrets.
I have treated about 40 ferrets with either Caparsolate
or Immiticide and the survival rate is about fifty percent
(50%) with each drug.
I do not recommend Immiticide to treat adult heartworms
in ferrets. A new drug called ProHeart (moxidectin) shows
great promise as an adulticide in ferrets, although it is
marketed and approved only as a preventive for dogs.
ProHeart is an injectable heartworm preventive administered
every six months. In the dog, it does not have the capability
to kill adult worms at the recommended dose. It does, however,
kill all larval stages of the worm. Since adult heartworms
in ferrets tend to be stunted and do not achieve the size
and reproductive ability they do in dogs, this may make
them more susceptible to moxidectin in the ferret.
I have used ProHeart in four heartworm-positive ferrets
with excellent results. All four ferrets not only survived,
but thrived and tested negative six to twelve months post-injection.
All ferrets received a single dose of 0.1 cc’s regardless
Much more research is needed to prove consistent efficacy
and safety, but ProHeart is the best treatment option I
have found to date. In our hospital, we now also offer ProHeart
as an option for heartworm preventive in ferrets
Please remember that this drug, like almost every other,
is not approved for use in ferrets, and you must understand
there is not much information available on its use in ferrets.
Prevention is the preferred method of dealing with heartworm
in ferrets. It is important to stress that living indoors
in endemic areas does not eliminate the need for administration
of heartworm preventive. Many cases of heartworm disease
have occurred in ferrets that have seldom or never been
The oral administration of a monthly dose of liquid Ivermectin
diluted in propylene glycol is dependable and safe. Simply
add 0.3 ml’s of 1% Ivermectin injectable to one ounce of
propylene glycol, making a 100 microgram/ml solution. Dose
this at 0.1 ml per pound of body weight (10 micrograms per
pound) once monthly. It should be dispensed in an amber
bottle and given a two-year expiration date. This method
has been used and recommended by me for over ten years and
I know of no cases in which a ferret has become infected
while on this regimen.
Heartgard® for Cats monthly tablet may prove to be a
useful alternative. Although the chewable dog tablet is
effective, most ferrets will not ingest the entire tablet,
but the feline tablet is much smaller and more readily consumed.
In a test conducted in my hospital, about sixty percent
(60%) of ferrets found the tablets attractive and palatable
and did consume the entire dose willingly. Placing a few
drops of Ferretone on the tablet makes it even more palatable.
ProHeart injectable heartworm preventive also appears
to be safe and effective in ferrets. We have been using
it in our hospital since 2002 and to date have not had any
bad reactions or problems with it.
The recent recall of ProHeart from the veterinary market
presents a common problem for practitioners who treat patients
other than dogs and cats. Since most drugs used in exotics
are used off-label, the FDA has little knowledge of their
success or failure in so-called minor species. Whether or
not ProHeart returns to the market in an approved form for
dogs and cats, it is to be hoped that it may continue to
be available to practitioners under the new Minor Use Minor
Species Act (MUMS).
It is apparent that there is still much to be learned
about heartworms in ferrets. Further study of survival rates
of treated versus non-treated animals would be very useful,
as would more information on safe and effective adulticide