The dog park is getting busy as you corral your dog for the last time. After many declined invitations to ‘“Come,” your dog suddenly stops, looks, and hurtles toward you at full speed. You laugh and put your arms around their neck, and see a mosquito with its needle-nose already piercing your pet’s flesh as you clip on the leash. 

Unbeknownst to you, the mosquito is carrying heartworm disease.

Six months later, you take your dog for their veterinary wellness visit. The veterinarian draws blood for a heartworm test. You naturally hug your dog around their neck during the procedure, and you remember that mosquito.

The moments that follow can go two different ways. Which ending will you choose?

If your dog has been receiving heartworm prevention, skip to the last paragraph—but if your dog has missed some doses, you forgot to purchase preventives, or they have never received heartworm prevention, read on.

What is heartworm disease?

The American Heartworm Society defines heartworm disease as “a serious and potentially fatal disease in pets in the United States and many other parts of the world. It is caused by foot-long worms (i.e., heartworms) that live in the heart, lungs, and associated blood vessels of affected pets, causing severe lung disease, heart failure, and damage to other organs in the body.” 

Heartworm disease is transmitted when an infected mosquito bites your pet, and injects microscopic heartworm larvae with the bite. From there, a process of maturation and migration occurs, as the larvae go from the bite site to their namesake, the heart. These larvae move steadily through your pet’s bloodstream over the span of four months, and arrive at the pulmonary (i.e., lung) vessels. There, the young heartworms finally transition to one of the large heart chambers where they mature into adults. At six months post-bite, the worms begin to reproduce. The larvae, known as microfilariae, enter the bloodstream and can be picked up by the next mosquito that bites your pet. The infection cycle can then begin again in another unsuspecting animal.

How does heartworm disease progress?

As the worms mature, they take up more space in your pet’s pulmonary vessels, which become inflamed, leading to thickening, and causing respiratory signs. Early stage signs in dogs often include a persistent cough and a reluctance to exercise. As the aging mature worms, which can live up to five to seven years in dogs, die, they often become lodged in the small vessels. The body responds by forming a clot, and the worsening blockage leads to diseased lung tissue, circulation problems, and ultimately heart failure.

Cats are affected differently by heartworm disease. Cats do not often carry mature heartworms, and do not show mild signs. Instead, they show respiratory signs of varying intensity, and may also experience incoordination, weakness, seizure, collapse, and sudden death. 

What is the treatment for heartworm disease?

The only current treatment for heartworm-positive dogs is an injectable drug called melarsomine, administered deep in the muscle over at least two treatments. This medication, which works by killing adult heartworms, is a painful treatment for dogs and requires a long period of restricted activity to prevent damage to the heart and lungs as the dead heartworms circulate. 

No heartworm treatment is available for cats or ferrets, but both species can be given supportive care with veterinary management. 

What is a heartworm test?

A heartworm test is a diagnostic screening recommended yearly at your pet’s wellness visit. Heartworm tests can be performed on dogs, cats, and ferrets. Testing works by analyzing a small blood sample for the antigen (i.e, protein) of the larval heartworms, which allows for rapid intervention and treatment, if available, should your pet test positive. 

Making a choice for your pets

Heartworm disease continues to affect more than a million pets per year. But, something can be done—heartworm disease is preventable. A wide number of prescription heartworm prevention medications are currently available, including cat- and ferret-safe formulations. These products come in convenient oral doses, topical applications, and injections administered at some veterinary practices. Most preventives work by breaking the heartworm life cycle at the larval stage, so that the microfilariae cannot mature into heartworms and cause clinical signs.

Preventives require commitment, with year-round dosing recommended for consistent protection. Only one missed monthly dose can open the window of opportunity for heartworm infection. We recommend setting up a phone reminder so you don’t miss a single dose!

The test results are in

Dog on prevention, read here:  There is a soft knock on the exam room door. Your dog’s ears perk up as the veterinarian walks back in, gives you a warm smile, and tells you the results are negative, with no sign of heartworm disease. You are commended for consistently keeping your furry companion on heartworm preventives year-round. That definitely pays off. The veterinarian reviews your current product of choice, and lets you know your refills for the next year are waiting at the front desk. If this is you, great job! Country Valley Veterinary Clinic celebrates every negative heartworm test, although we still recommend you read this entire post!

Dog not on prevention, read here: We’re not going to give you a sad ending, because this is the beginning for you and your pet. We’re confident that you now understand the heartworm disease risk, and you are ready to discuss prevention options for your beloved pet. Call to schedule an appointment—and a heartworm test—at Country Valley Veterinary Clinic.