The WHYS of year round heartworm prevention

posted: by: Sarah Sims, DVM Tags: "Clinic Specials" "News" 

Why does my dog need ____________?

With enough information to fill thousands of libraries at the tip of our thumbs, it is becoming increasingly rare to trust a healthcare professional's advice without fact-checking on the internet.  I am certainly just as guilty of it as most of my clients.  And I will be the first to admit that I'm doing my own internet research with nearly all of my non-routine appointments.  New information emerges way too fast to keep up with all of it, and I have an unhealthy fear of doing something that does not have evidence to back it up.

There is nothing wrong with asking your veterinary health professionals questions.  In fact most of us LIKE explaining why we are doing what we are doing, because this stuff fascinates us.  All we ask is that you ask these questions with a curious heart rather than an accusatory one.  I can't speak for every veterinarian, but most of us truly want the best for you and your pet, and it is heart wrenching when we are accused of feeling otherwise.

So, since I am new to this practice and have a lot of trust to earn, I would like to share with you the "Whys" of the most common recommendations at your annual visits. 

Today's Topic: Year Round Heartworm Prevention

I follow the American Heartworm Society's recommendations of year round heartworm prevention in dogs AND CATSThis means giving a full dose on the same day each month, every month, for life.  I know what many of you are thinking: "But I thought heartworms were carried by mosquitos.  How do mosquitos infect my pet in the winter, or for that matter, my indoor cat?"  Those are totally valid questions!  This is where it gets complicated and I am going to anthropomorphize because it is more fun that way.  I will use my dog Red as an example.  Here is a picture of Red worrying about the daily threat of heartworm disease:


Baby heartworms start out in an infected dog's blood.  When a mosquito bites them, it picks up these babies and fosters them for 14 days while they grow into toddlers.

When that mosquito bites Red, the toddler heartworms enter his skin where they hang out for about a month to become teenagers. 

Then, the teenagers make a 6 month-long journey to Red's heart, where they grow up, buy a house, and mate for SEVEN YEARS before they die. 

Monthly heartworm prevention does not prevent Red from being infected entirely.  It simply kills any toddlers he may have picked up over the past month, before they make it to his heart to cause permanent damage as adults.  Preventions cannot kill teenagers or adults. 

Now here is what can happen if you start gambling with heartworms (hint: the house always wins):  If I don't give November's dose, and Red was bitten by an infected mosquito in October, the toddlers will grow up and Red will have heartworm disease.

Here's where it gets even more sketchy: We cannot detect heartworm infections with our tests until the heartworms are fully-grown adults.  In the previous scenario, we would not be able detect heartworm disease until April, even though Red was infected in October!

Even more harrowing, it only takes a few days of 50 degree weather for mosquitos to re-emerge in the winter.  In the Midwest, we have several thaws throughout the winter that will put our pets at risk if they are not protected. 

If that's not enough evidence, lets look at it from an economic standpoint.  Getting rid of adult heartworms costs 10-15x that of a year's worth of prevention, and it does not reverse any damage done to the heart.  Prevention costs less than 50 cents per day for most pets.

A note on cats: The heartworm life story in a feline is different and I will lose you if I go into it today (If I haven't already).  The most important fact to know, is that in one of the biggest studies on feline heartworm disease to date, 30% of cats infected with heartworms were kept strictly indoors.  As an indoor-cat owner, I don't like those odds.

Year round heartworm prevention is not about profit to us.  It is about taking advantage of the opportunity to completely prevent a deadly disease from harming the pets we get out of bed for each day.

For more information, see our care guides to your right, or visit the American Heartworm Society website.

Tomorrow's Topic:

Vaccines: Which ones does my pet really need and why?