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Heartworm Disease In Ferrets

R. S. Hines DVM PhD

You can read a 2017 update on heartworm disease, prevention, diagnosis and spread here.

Advantage Multi for ferrets here

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The heartworm, Dirofilaria immitis , is actually a true parasite of dogs.

How Would My Ferret Get Heartworms ?

For your pet to get heartworms, it must be bitten by an infected mosquito.

Heartworm disease is uncommon in ferrets because most people keep their pet ferrets indoors. But if your ferrets catches a few of these worms the results are often fatal.

Mature heartworms normally live in the right side of the heart of infected dogs - not ferrets. Female heartworms pass millions of microscopic larva into the bloodstream of these dogs. From there, they are sucked up by mosquitoes catching a meal on the dog’s skin.

But heartworms can mature in the hearts of ferrets too. If the infected mosquite leaving the dog later bites your ferret, the larval heartworms slowly migrate to the ferret’s heart where they develop into mature parasites. Heartworms come in both male and female, ranging in size from the smaller 3-inch males to 6-8 inch females. It only takes a few female worms to seriously plug up the circulatory system of a ferret.

Who Should Worry About Their Ferret Getting Heartworms ?

If your ferret doesn't get bitten by mosquitoes, it will not contract heartworms. Most owners of ferrets who live in houses that have window screens are safe from mosquitoes. But if mosquitoes within your house are a problem for you, they are a problem for your ferret too.

Where ever heartworms are a problem in dogs, the mosquito population carries heartworms. If you live in wet, semi-tropical areas of the US, mosquitoes are more likely to carry heartworm larva. If you keep your ferret outside in these areas, your ferret should receive a monthly heartworm preventative.

What Signs Would I See If My Ferret Had Heartworms ?

Symptoms of heartworm infection in ferrets are not the same as in dogs. Because the ferret heart is smaller than most dog hearts, it takes less worms to cause heart failure in ferrets.

In dogs, the first signs of heartworm disease are gradual and usually caused by chronic irritation of the lining of the heart and arteries of the lungs.

Ferrets react more similarly to cats when they develop heartworms. Like cats, ferrets with heartworms suddenly have difficulty breathing. Their gums turn pale and grayish and their pulse is rapid. This is because the heartworms have blocked the blood passageway from the heart to the lungs.

When one listens to their chest with a stethoscope, heart murmurs may be present, the heartbeat may be irregular and lung sounds congested.

Ferrets with heartworms occasionally cough and fluid may back up into their abdominal cavity and lungs, but more often, the only sign of infection is general weakness. Some cases are easier to recognize because these ferret, cough, have trouble breathing and their heart sounds are abnormal.

X-ray of these ferrets may show and enlarged heart and pulmonary edema. Death is often sudden without heartworms entering the owner or veterinarian’s mind.

How Would My Veterinarian Know My Ferret Had Heartworms ?

Several of the tests we use to detect heartworms in dogs do not work in ferrets. That is because the simpler tests rely on finding baby heartworms in the pet's blood. These immature heartworm larva are not found in infected ferrets. The other common test is for products that adult heartworms release into the pet's blood. But ferrets are so small that the 1-2 worms that might be present, don't release enough of this material to be detected. A test marketed by Idexx to check cats for similar low numbers of heart worms may be the best current option.

Occasionally, the worms can be seen in an echocardiogram examination that utilizes doppler and ultrasound to visualize the heart and blood flow.

Is Their A Treatment For Heartworms In Ferrets ?

Treatment of heartworms in ferrets is quite difficult and often unsuccessful. This is because the small diameter of the blood vessels exiting the ferret heart make them prone to plugging with dead worms after the treatment. No product is approved by the Government for this use. Approximately half of ferrets treated with the heartworm-killing drug, Immiticide do not survive.

Many veterinarians give a corticosteroid (prednisone) during treatment to try to prevent life-threatening blood clots.

For a time, moxidectin (ProHeart) seemed to offer potential. It did not kill the heartworms as rapidly as Immiticide, so the chances of arterial worm blockages appeared less. It was only approved for heartworm prevention in dogs. It was removed from the market due to side effects but It reappeared on the market in 2008. In dogs, it only prevents new heartworm infections. But it appears to sometimes cure them in ferrets. [ Note: Advantage Multi contains moxidectin and is approved for use on ferrets] (ref)

Ferrets should be caged and not allowed to exercise during and for one month subsequent to treatment .

Following treatment, a SNAPS feline heartworm test should be done every two months to determine if the worms were killed.

How Can I Prevent My Ferret From Getting Heartworms ?

You can see why preventing heartworms is much preferable to treating them. If you live in a high heartworm area and your ferret is subject to mosquito bites, it is wise to keep your ferret on a monthly heartworm preventative. Although the risks are quite low, heartworm-carrying mosquitoes can and do bite indoor ferrets. The preventative of choice for ferrets is ivermectin. Many ferret owners purchase Heartgard for cats or a similar ivermectin product and give one half tablet to their ferret every month (or a portion appropriate for its current weight). If your ferret will not eat it readily, wrap or crush it in tuna or liver paste. Some ferret owners find that the <25-lb dog tablet can be broken into quarters and a quarter given monthly.