APRIL 18, 2019
What You Need to Know about Heartworm and Dogs

Heartworm disease in dogs is serious. So serious that it can cause heart failure, damage to other organs, lung disease, and even death. Itโs a condition spread by bites from infected mosquitoes, and taking the correct steps to prevent it in dogs is Good Dog Ownership 101. In some parts of the country, even in very early spring, over-wintering infectious mosquitoes may already be a concern. Hereโs what you need to know about heartworm in dogs during any season.
What is Heartworm in Dogs?
Heartworm disease, also known as dirofilariasisis is caused by a parasite calledย Dirofilaria immitis, which is a blood-borne parasite. After the parasite (now in a larvae state) is transmitted to a dog via bite from an infected mosquito, the parasite finishes its life cycle in the dog. With the dog as host, the larvae move through the bloodstream and settle into the heart and surrounding blood vessels, where the larvae mature to adults within 5-7 months. Heartworms resemble strands of spaghetti, and a diagnosed dog can have anywhere from 15 to 250 or more in their system.
IMPORTANT FACT:ย Dogs cannot get heartworm from other dogs.
What Can Heartworm Do to Dogs?
Because it takes time for the worms to mature and start reproducing, the disease is very rarely seen in puppies one year old are less. In fact, itโs most often diagnosed in 2- to 8-year-old dogs, when clinical signs become apparent and the worms have already multiplied. Heartworms can:
- Clog heart vessels
- Clog the pulmonary artery
- Affect the valve action in the heart
- Cause major damage to other organs, since the worms interfere with the blood supply from the heart
What are the Symptoms of Heartworm in Dogs?
The more severe the symptoms, the worse the dogโs condition, as you would expect. Signs of heartworm disease can manifest itself in any combination of the following:
- Coughing
- Nose bleeds
- Pneumonia
- Aversion to exercise

Are the Chances of Heartworm Infection Greater in Springtime?
A dog can be infected with heartworm any time of year when mosquitoes are prevalent, so in warmer climates, you can expect the heartworm โseasonโ to last much longer. That being said, once mosquitoes are present, the risk begins; so if youโve had an unusually warm early-spring or live in an area where over-wintering mosquitoes exist, itโs time to start seriously thinking about heartworm prevention. The map below has the latest stats (collected in 2016โthe next map will be issued later in 2019) for where heartworm was most prevalent.

Whenโs the Best Time to Start Heartworm Prevention Meds?
As with anything else, itโs best to consult your vet. But the rule of thumb for the best time to start heartworm prevention medication is 30-45 days after the weather warms up enough for mosquitoes to appear. Once your puppy reaches 5 months (or if you adopted your 5-months-plus dog from a shelter) vets recommend testing for heartwormย firstย before starting any preventive regimen. The meds can be given at home or at your vetโs office, if you prefer.
The Tip of the Tail
Itโs obvious that heartworm is a disease we should take active steps to prevent in our dogs, but itโs important to remember that not all mosquitoes cause heartworm, and that the problem is not epidemic. As with everything else, consult with your vet on the best course of action for your dog.
SOURCES
Center for Veterinary Medicine. โAnimal Health Literacy โ Keep the Worms Out of Your Petโs Heart! The Facts about Heartworm Disease.โย U S Food and Drug Administration Home Page, Center for Veterinary Medicine, 31 July 2018, www.fda.gov/animalveterinary/resourcesforyou/animalhealthliteracy/ucm188470.htm.
โHeartworm in Dogs.โย American Heartworm Society, 19 Apr. 1970,ย www.heartwormsociety.org/heartworms-in-dogs.
Kent, Chelsea. โHeartworm Facts: Prevalence, Medication And Alternative Treatment.โย Dogs Naturally, 18 Mar. 2019, www.dogsnaturallymagazine.com/heartworms-in-dogs/.
Ward, Ernest. โHeartworm Disease in Dogs.โย vca_corporate, vcahospitals.com/know-your-pet/heartworm-disease-in-dogs
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