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Have
a Heart: Protect Your Ferrets from Heartworm
© Erika Matulich, Ph.D.
Just
one little mosquito bite: That's what infected my ferret Tigger with the
single heartworm that took her life at the tender age of 3.
The survival rate of ferrets infected with heartworm is poor; prevention
is the key to saving your ferret's life. And prevention is very easy! If
you live in an area where even one mosquito could enter your home, your
ferret should be on heartworm medication. In some parts of the world,
this means monthly medication during the mosquito, or wet, seasons. But
where I live, in Florida, a year-round medication regimen is a
necessity.
Heartworms are a type of roundworm parasite
called Dirofilaria immitis. This parasite is common in all sorts
of species, including dogs, cats, ferrets, raccoons, skunks, otters,
horses, pigs, and even people. Of all these critters, only the canines
(either wild, like wolves and coyotes, or domestic, like our pet dogs)
are “definitive” hosts, or hosts where the heartworm can reproduce.
All other animals are “dead-end” hosts, meaning the heartworm can
infect them and live in them, but can't breed.
When a mosquito bites a canine infected with heartworms, it sucks up the
microscopic heartworm larvae. These larvae continue to develop in the
mosquito, and the mosquito deposits the parasite into its next victims.
Mosquitoes can travel several miles from their hatch site, biting and
infecting many animals as they go.
Keeping your ferrets indoors can somewhat reduce the risk of heartworm
infection, but it can't eliminate the risk, because mosquitoes do get
past those screens! In fact, nearly half the cats and almost all the
ferrets infected with heartworms are strictly indoor pets, as Tigger
was.
Once the heartworm larvae enter the new victim, they travel through the
blood vessels, taking between three and six months to reach the heart.
Once in the heart, the parasites lodge in the right ventricle and begin
growing into adult worms that can reach a length of 12 inches. The worms
can also invade the lungs and block blood supply to the liver. Because
of the small size of the ferret's heart and lungs, even a single
heartworm is enough to kill a ferret.
A ferret may show several different signs of
heartworm, depending on how many worms there are, how big they are, and
where they are growing. The most common “symptom” for a ferret is
sudden death from heart failure, and this is what happened to Tigger.
If your ferret does show signs of infection, these may include reduced
activity and tiring easily during exercise; coughing; rapid breathing;
fainting; development of a pear-shaped stomach (because of fluid
buildup); and a bluish color to the tongue, gums, and lips.
Unfortunately, some of these signs resemble the symptoms of other ferret
diseases (such as insulinoma, lymphoma, and heart disease). But if you
have any suspicion of heartworm, don't delay in seeking professional
treatment; a wait-and-see attitude could kill your ferret.
To check for heartworms, your veterinarian should use an “occult
heartworm” test. Because these tests measure the amount of a specific
protein found on the heartworm's skin, they can detect the presence of
hidden infections.
For dogs, vets commonly take a blood sample and look for heartworm
microfilariae (larvae) under the microscope, but in ferrets these are
not present (or are not present in large enough numbers to be detected).
Deborah Kemmerer, D.V.M., a noted ferret heartworm specialist,
recommends the Snap® Heartworm PF Antigen Test (made by IDEXX) as the
most dependably accurate heartworm test for ferrets. A set of X-rays and
an echocardiogram can also help support a blood-test diagnosis by
showing any changes in the heart and lungs.
There are a number of treatments for animals infected with heartworm,
but not all work well for ferrets. For example, in larger animals, adult
worms can be removed surgically or killed with the drug Immiticide. But
these procedures have not shown a high success rate in ferrets.
Kemmerer recommends the drug Caparsolate. This drug must be administered
intravenously by a vet in a series of six injections (two shots 12 hours
apart, wait four weeks, and then four shots 12 hours apart). Ideally,
your ferret should be boarded with the veterinarian during this time,
because extra activity can cause a fatal embolism (blood-vessel
blockage) from the dying adult worms. Ferrets who undergo this treatment
show about a 60 percent survival rate.
It's much easier (and less expensive) to
prevent heartworm than to treat it after the fact. A monthly oral
heartworm preventive is the way to go. One option is to use the monthly
Heartgard pills for cats. Get the product for cats weighing up to 5
pounds, and cut the pill in half. (Most ferrets weigh 2 to 3 pounds, so
half the cat dose is plenty.) Then crush the half pill into a powder and
mix with Ferretone or Nutrical. There are also chewable tablets, which
some ferrets will eat like treats. Again, get the product for cats up to
5 pounds; ferrets can take the whole cat dose for chewable tablets.
My favorite monthly heartworm medication is a liquid made up by my vet
of 0.3 cubic centimeters of 1 percent, injectable ivermectin mixed with
an ounce of propylene glycol. This solution is inexpensive (ideal for
multiferret households!) and has a long shelf life. Each ferret gets a
dose equal to 0.1 cubic centimeter per pound of body weight. On the
first day of each month, we set up the postal scale, weigh each ferret
(and record weights on a chart), and use a little oral syringe to squirt
medicine in each mouth. The medicine apparently doesn't taste that
great, so we follow up with a liberal dose of Linatone as a treat.
So what happened to Tigger? Although she had been receiving heartworm
medication while I owned her, she apparently had gotten her single worm
from a mosquito bite before I rescued and adopted her. The heartworm
preventive will stop any new adults from attaching to the heart and
growing, but it won't necessarily kill existing adult worms. After
Tigger's surprising demise, I was quick to test all my other ferrets for
heartworm. Fortunately, everyone else was fine. And with the easy
monthly prevention regimen, they'll stay heartworm-free!
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