Mesa Veterinary Hospital

Heartworm Disease

May 12, 2017
Posted By: Mesa Veterinary Hospital
Heartworm Diagram | Mesa Veterinary Hospital

Heartworm season is coming!  Starting June 1st we recommend that all Colorado dogs be on monthly heartworm prevention.  You are likely getting phone calls from us to update your dog’s heartworm test and pick up heartworm preventative. But…. Why?  I will tell you!

Heartworm disease, also called Dirofilaria immitis, is truly a worm that can live in a dog’s heart and pulmonary (lung) arteries.  It can also be transmitted to cats and ferrets but very uncommonly.  This worm can grow up to 14 inches long!  Gross!

Heartworms are spread by mosquitos so a dog does NOT have to be interacting with other dogs in order to get the infection.  Puppies can also get heartworm disease from their mothers when they are in the placenta.  Some of the mosquitos that like to carry heartworms also like to live in our houses, so your dog does not necessarily need to spend a lot of time outside in order to get the infection.  Treatment for a heartworm infection is very difficult and expensive.  Prevention is very easy, relatively inexpensive, and almost 100% effective.

At Mesa we recommend that every dog in Colorado get an annual heartworm test.  Though the chances of your dog getting heartworm disease is low, it is possible and you definitely want to catch a positive dog on a test and NOT when they are showing signs!  If they are already showing signs of the infection, they could be in very big trouble. Even if your dog is taking heartworm prevention as they should, the preventative is not 100% effective and if you’re like me at all you may be a few days late a month or two, which leaves your dog at risk for infection.  A heartworm test is a little blood test and is very accurate.

We also recommend dogs in Colorado take a monthly preventative June through November.  These preventatives kill baby heartworms that your dog may have been infected with before they can cause any damage to the body.  Most heartworm preventatives also help with gastrointestinal parasites as well.  There are many types of heartworm preventatives but the ones we carry are ivermectin (Heartgard), selamectin (Revolution) and Milbemycin (Interceptor).  If your dog travels outside of Colorado, there may be other recommendations for heartworm prevention use.  Please discuss your travel plans with us so we can make sure your pup is protected!

When a dog is infected with heartworm disease it actually can take 6 months before the heartworms are detectable because the tests look for adult heartworms.  This is why we do not test puppies under 6 months of age for heartworm disease.  As discussed, adult heartworms travel to the heart and blood vessels in the lungs and they grow… and grow… and grow!  The dog’s own immune system will try to defeat the worm, but they are unable to.  In the process they produce a lot of inflammation that can damage and scar the heart and blood vessels.  Blood flow is abnormal in these areas and life threatening clots can form.  Some arteries are completely blocked by the number of worms, which then cannot circulate blood or oxygen as they should.  Worms that die in the dog can move and clog the lungs.

It can actually take a very long time for dogs to show signs that they have heartworm disease.  Signs can include coughing, shortness of breath, exercise intolerance, fluid accumulation in the chest or abdomen (because the heart is failing), and even sudden death.

Heartworm disease is a very damaging and sometimes fatal disease that we take very seriously!  We are lucky in Colorado.  Because of our cool nights and low humidity, heartworms have a hard time replicating.  However, we still see it every year (we’ve had two cases already this spring) and it is a terrible disease.  If you haven’t already, make sure you get your pup in for his annual heartworm test and pick up your heartworm preventative!

Our Lobby is Open!

We are happy to welcome our clients back into the lobby! The hospital is open and at this time face masks are optional inside the building for anyone who wishes to enter. Please call us with any questions or concerns at 303-237-9542. Our team can also be reached by email at