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Let's get to the heart of the matter - Heartworm!

Ok, now for those pesky heartworms!

Is that really a thing (you type into google)?

Hopefully that search lead you here!

I admit, I feel like heartworms are old news, especially when new and more impressive parasites are in the news like ticks ( and fox tapeworms (

The perennial heartworm though seems to remain mysterious to many, and still blog-worthy. It is midway through June, and not too late to start your pet on heartworm prevention for 2019.

I have personally been dined on by many mosquitos and black flies already this year (check out my black fly blog So, I can vouch the mosquitos are up & hungry. Mosquitoes are the creature of interest today because they are the heartworm “vector”. We can’t have heartworms without those mosquitoes.

The most likely source of the heartworms are coyotes (the “reservoirs species”). Mosquitoes bite coyotes with heartworms and then bite pet dogs, passing the baby heartworms along as they dine. I continue to be surprised by how many coyotes I see in Cobourg, so I feel confident in saying we have a potential reservoir literally in our backyard. Another potential “reservoir” is imported dogs. The importation of adult rescue dogs into Canada continues to increase, and many of these dogs come from places with lots of heartworms.

Do we really know heartworms are in our area? I really wasn’t sure until 2017. We did pick up positive cases, but usually the dogs had some history of travel, so I wasn’t convinced it was in our area. Then I had a case that convinced me. In 2017 I had a patient “Rufus” who we had tested negative in 2016, did not use monthly prevention in the summer of 2016, and was positive for heartworms in spring 2017. We confirmed the positive test by looking at the baby heartworms under our microscope. “Rufus” had never traveled, hadn’t even left home in years. This case solidified for me that heartworms are here in Northumberland county.

At this point in the conversation I hear a variety of questions and statements that usually revolve around treatment. Some say, “well, you can just treat it if they get it”. This is true. We did successfully treat “Rufus” in 2017. The trouble is that ideal treatment involves several medications, some of which are not very pleasant, and at least one of which is reasonably expensive. And so, like many a veterinarian before me, I could take a stack of basic heartworm preventative medication chews and say: “you can buy a lifetime of prevention for less than what it would cost to treat heartworm just once”. I think this sentiment is fairly accurate. However, this reason focuses just on money. The bigger issue is that these are nasty bugs, and money cannot solve everything.

These worms really do shorten dogs lifespans and cause heart failure. Which usually brings us to the question “what are the symptoms of heartworms? Ah, there is the tricky bit. I can & will tell you the symptoms of heartworm disease, but the real key is: By the time a dog has symptoms of heartworm infection the parasites have already done irreversible damage to the heart. This I have also witnessed firsthand, usually in dogs that have been adopted from the USA. People adopt dogs with active heartworm infection that have symptoms (coughing, lethargy, heart murmur). They treat the pet and kill all the heartworms. The tests all go negative - they are really all gone. They dutifully give prevention - these pooches are not getting new infections. The dogs still have heart disease, their heart murmurs do not go away, and they generally live shorter lives.

Which brings the conversation around to heartworm testing. I can write a separate blog on the purpose of heartworm testing, but the best reason to test is to find heartworm infections early, before the dog has any symptoms. If the infection is caught early and treated effectively, the dog should go on to live a normal & healthy life - as did “Rufus”.

A heartworm test involves a small blood sample. I am going to repeat: blood sample. I repeat this, only because it is a common confusion that arises because we also frequently check stool samples for “worms”, however, we cannot find heartworms in stool because they only live in the blood vessels. The heartworm tests are now usually bundled with tests for tick diseases, so we also pick-up exposure to other blood-borne pathogens on the same test.

For fear of being too verbose, I am going to leave my heartworm conversation here for today. I will strive to follow up with some more fun info very soon - so stay tuned! It is truly not too late to keep your pets protected against heartworm infection for 2019 - give us a call at: 905-372-2721.

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