Canine heartworm prevention

Monday, January 05, 2015

So, this time I’d like to take a minute and talk about heartworms. If you own a dog you’ve probably heard about heartworms and that they can be devastating. We routinely recommend all dogs (and cats) be on some type of heartworm preventative and I’d like to explain what the big deal is and why we’re so adamant and committed to talking about it.

I’ll save you a lengthy discussion on the heartworm life cycle, but the key thing to know is that they’re spread by mosquitoes. Heartworms live in the chamber of the heart that leads out the blood vessels in the lungs. This means that the worms are interfering with the heart’s ability to pump blood to the lungs. This is bad. Very bad. A full-blown infection will almost completely clog the artery leading to the lungs and will eventually kill the dog through congestive heart failure.

The good news is that heartworm disease is treatable, but the bad news is that it is very tricky to pull it off. Because the worms are sitting just before the lungs when we give medication to kill them they drift out of the heart and into the lungs causing blockages in the blood vessels supplying the lungs as well as causing massive amounts of inflammation and damage. We get around this by using smaller amounts of medicine and treating multiple times to kill the worms off slowly, but it’s still very dangerous. So you can see why it is much easier to prevent heartworms.

Now why am I writing this in the dead of winter instead of the dog days of summer when mosquitoes outnumber people? A lot of people stop their heartworm medication in the winter because there aren’t many mosquitoes flying around and because it’s too cold for the larvae to grow in the little buggers. The problem is that it is still possible for them to get infected. Not only that, but at some point it’s going to get warmer and mosquitoes and larvae will start creeping back and it’s impossible to know exactly when that will be. Waiting until you see the first mosquito may be too late. So it’s just safer to keep your pets on preventative year-round to eliminate the possibility that they might get infected.

There’s also the added bonus that the medication will also handle other parasites your pets may pick up. Our winters may feel really cold and your car windows may be frosted over in the morning, but around here they aren’t cold enough to really kill all the parasites out there.

But that’s enough discussion for now. Next month: Cats. Why do they need heartworm preventative? 

by Jeffrey Sargent, DVM