Tuesday, May 19, 2015

Heartworm: A Very Different Disease in Cats vs. Dogs



Both dogs and cats are susceptible to heartworm infection from mosquitos.  However, the unique differences between each species means that heartworm disease in cats is very different than in dogs.  Cats are not a natural host for the heartworm parasite, Dirofilaria immitis.  So, when a cat is bitten by an infected mosquito, the cat’s immune system is able to kill most of the immature worms (microfilaria) before they reach adult life stages.  Therefore, only a few worms usually reach adulthood in cats.  Heartworms thrive in dogs, however, because dogs are a natural host of heartworm.  A dog may have upwards of 50 worms inside him.  

Unfortunately, it takes only one adult worm in a cat to cause clinical signs such as respiratory distress, coughing, vomiting, and even death.  Furthermore, the immature worms and the cat’s own immune response to them can cause asthma-like lung disease with lifelong symptoms, known as Heartworm Associated Respiratory Disease (HARD).   In dogs, it is usually only the adult worms that cause problems by damaging the heart and surrounding blood vessels.  These dogs often develop a cough, which can progress to difficulty breathing, weight loss, and ultimately heart failure and death.  

Heartworm is easily diagnosed in most dogs with a simple blood test which detects the presence of adult worms.  Because infected cats usually only have 1 to 3 worms in their bodies,  there are often too few worms for the blood tests to detect.  Diagnosing heartworm infection in cats can be very challenging because false negative test results are common. When a dog is diagnosed with heartworm, there is an FDA-approved medication to eliminate heartworms.  However, since there is NO approved treatment for heartworm infection in cats, the best we can do is try to manage the cat’s condition and symptoms.  The good news is that heartworm is easily preventable in BOTH cats and dogs with year-round medication.


  • By:  Stephanie Brittin, DVM

6 comments:

  1. I didn't know that heartworms are different in cats and dogs. It's important to keep up on your dog's health. They will need more care when it comes to heartworms. It's definitely good to know that cat's immune systems are able to kill most immature worms, like you mentioned. This is interesting. http://www.pahlincoln.com/

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  2. I didn't know that heartworms are different in cats and dogs. It's important to keep up on your dog's health. They will need more care when it comes to heartworms. It's definitely good to know that cat's immune systems are able to kill most immature worms, like you mentioned. This is interesting. http://www.pahlincoln.com/

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  3. Heartworms sound very unpleasant. I'm very glad I came across this article. My son brought home a dog a few weeks ago, and I told him he could keep it. Having a pet is a big responsibility, so I want to be sure that Chuckles, the dog, is well taken care of. I'll have to schedule an appointment for him at an animal clinic to have him tested for heartworms.

    Susan Hirst | http://www.colorado-vet.com/about.html

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  4. I didn't realize that heart worms were different in dogs and cats. I just got a cat and I figured we'd just take the same preventive measures that we did with my dogs. It sounds like it's much more serious in cats and the signs show up a lot quicker. We'll have to find a good vet to take the cat to regularly to have him checked for heart worm. http://www.smallcreaturespetclinic.ca/en/what_we_do.html

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  5. I was very surprised to learn that it is so difficult to detect heartworms in cats. I own a cat, and it would be terrible if Bootsy were to have heartworm parasites. You said that they are preventable with year-round medication, so I better go to an animal hospital and get some for my cat.

    Susan Hirst | http://westlakeanimalhospitalinc.net/

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  6. Heartworms are a bad things for both cats and dogs, but I didn't know that 'the unique differences between each species meant that heartworm disease in cats is very different than in dogs' and needed to be treated as such. This is something that all pet owners should know about and be well informed of as well. That way they can go about treating their dog or cat the way that they need specifically. Information like this is the kind of things are really important for pet owners to know.
    http://oakhillsanimal.com/

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