Five Common Myths About Heartworm Disease in Pets

It’s that time of year again when we tend to think and talk about heartworm disease with our clients.  There is always misconception and confusion around this topic so let’s dig in.  Heartworm is a parasite that lives in the heart and blood stream.  Heartworm disease is transmitted by the bite of an infected mosquito.  Once the mosquito bites and the larva is in the dog’s bloodstream it takes it approximately 6 months to go through is various life stages to become an adult in the right chambers of the heart.  Imagine angel hair pasta inside your heart.  That makes it difficult for your heart to work over time and will eventually cause heart failure and other related diseases.  The hard thing is that sometimes heartworm infections don’t cause any symptoms other than sudden death.  The symptoms will sometimes show up before this happens thankfully and coughing is usually the first sign.  You may or may not see signs of fatigue, exercise intolerance, or collapse.

Myth #1:  Clients are always telling me that their dog does not have heartworm because they don’t see it in the stool, well you shouldn’t.  It does not live there; it is not an intestinal parasite, it is a blood parasite.

Myth #2:  The next thing clients tell me is that their dog does not live outside so it’s not at risk, wrong!  I hope your dog is going outside at least to go to the bathroom and hopefully for walks.  Also mosquitos do come inside our houses so all animals are at risk.  Indoor cats actually have a higher incidence of heartworm infections.

Myth #3:  My dog only needs to be on heartworm prevention for 6 months – well maybe, it depends on where you live but for the most part (and definitely in Colorado) they need to be on prevention all year round.  With our volatile weather all over the country nowadays it is possible for a mosquito to bite and infect your animal in those 6 months that you think you are safe because it’s “cold” out.  A random fact that I recently learned was that one mosquito can bite your pet 80 times in a single evening.

Myth #4:  My dog does not need to be tested yearly – yes they do and it is important for a number of reasons.  Just like all parasite medications, there are heartworms that have developed a resistance to the prevention.  If your dog is the unlucky dog to get one of these infections, we need to know about it so it can be addressed.  Your dog could have vomited up the medication without you knowing it and was not covered for a month.  User error also comes into play – a large amount of people forget to give it and may skip a month or two so that naturally makes them vulnerable.

Myth #5:  Cats do not get heartworm disease – false.  Cats do get heartworm disease just not as easily as dogs because they are not a normal host.  When cat’s get the disease from a mosquito it is hard to know because they may not show any signs.  They usually do not have as large of a worm burden as dogs and may only have 1 worm in their heart.  The test for cats is not as straight forward as it is for dogs because of this.

So the moral of the story – make sure your pet is on heartworm prevention all year round and test each year too.  This will save you much headache and money because treating a heartworm infection is expensive, has risk, and takes time and many tests to get rid of.  This is a very simplified explanation of heartworm disease so as always, consult your veterinarian with any questions or concerns you may have for your specific pet.

M. H. Archer, DVM
Loveland Veterinary House Call

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