A Little Prevention Can Save A Lot Of Heartbreak When It Comes To Heartworm

Heartworm is a problem in all fifty states and across a number of species but today we’re talking about dogs specifically. In New England the risk of contracting the disease is considered mild to moderate.  Below we’ve put together a handy primer on what heartworm is and why it’s important to protect your pup from it by using prevention.  Remember to always consult your vet before starting a medication on your pet!

What Is Heartworm?

Heartworm disease is caused by a parasite called Dirofilaria immitis.  It’s transmitted by mosquitoes which bite an infected animal like other dogs, coyotes or raccoons, pick up larvae along with the blood meal, and then transfers those larvae to your pet when it bites them.  The parasite larvae enter the bloodstream through the bite and make their home in the heart, lungs, and associated blood vessels, where they develop into full-fledged worms. Disease transmission is similar to the tick-borne transmission of Lyme disease.

When a dog contracts heartworm the larvae hatch, grow, and reproduce until the dog is hosting hundreds of adult worms. These worms clog up the heart, lungs, and larger arteries, multiplying and causing long-lasting damage.  If left untreated, the worms will eventually kill the host. Heartworm disease is difficult to treat once contracted but can be successfully prevented with medication.  

What Are the Symptoms of Heartworm in Dogs?

According to the American Heartworm Society:

Signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As heartworm disease progresses, pets may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen. Dogs with large numbers of heartworms can develop a sudden blockages of blood flow within the heart leading to a life-threatening form of cardiovascular collapse. This is called Caval Syndrome and is marked by a sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine. Without prompt surgical removal of the heartworm blockage, few dogs survive. (www.heartwormsociety.org)

How Is Heartworm Treated?

Once a dog contracts Heartworm treatment is expensive and lengthy.  Most treatment plans take 1-3 months to kill most of the adult worms through a series of injections.  Lab work will also be performed frequently to monitor the progress of the treatment.  Your vet will probably prescribe pain medications as well.  In severe cases surgery may be required.  Even once treatment is complete there are often long-lasting effects from the damage done by the worms.  The best option, therefore, is preventing your dog from contracting heartworm in the first place.


Preventative medication can come in several different applications such as injections, topical “spot-on” treatments, and chewable.  The most common are monthly chewable “treats” that contain medication to kill heartworm larvae.  These must be administered every 30 days to continue to protect your pup. Preventatives are available by prescription from your vet and are specific to the weight of your dog.  They cost $40-$50 for 6 months of chewable medicine tabs compared to $500+ for heartworm treatment once the parasite has infected the dog.

In conclusion, we think our partner veterinarian Dr. Jackie Fullerton at VCA South Shore Weymouth Animal Hospital sums it up best. “Heartworm disease is a serious, potentially fatal disease for pets that can be very painful and costly to treat. Fortunately, year-round monthly preventives are highly effective.  Working with a veterinarian is key to establish a plan for monthly preventative medication for your pet to prevent heartworm disease.”

Leave a Reply