Once upon a time, heartworm disease was a tragic condition that affected pets only in the southern United States. Other pet owners had to comply with monthly heartworm preventives and annual testing for their pets—but such precautions were unnecessary here in the blissful Pacific Northwest (PNW).

Unfortunately, this idyllic period has come to an end—heartworm disease has breached our fairy-tale world and stormed the castle. Heartworm disease is here—and affecting more pets every year.

No longer safe—heartworm disease is a real risk for PNW pets

According to the Companion Animal Parasite Council (CAPC), Washington state has had a 579% increase in heartworm positive pets since 2014. Recent statistics from 2019 to 2020 showed an increase from 461 heartworm positive pets to a staggering 731. And, these numbers are only a glimpse of the reality—CAPC relies on voluntary test data from veterinary practices, but estimates that their numbers represent only 30% of actual heartworm positive pets.

For May 2019, Salem, Oregon, was ranked number one for the highest monthly number of heartworm-positive test results in the country—a recognition no one wants to receive. And from 2019 to 2020, CAPC reported that the state’s positives nearly doubled.

So, how does an area once virtually untouched by this devastating disease suddenly become a hotbed? The answer involves multiple factors—some inevitable and beyond human control, but others that can be changed for the better—but only with your help.

Change is in the air—why more pets are getting heartworm disease

What’s causing this increase, and how can we stop this disease from spreading? Known contributors to the great northwestern heartworm disease migration include:

  • Climate change — Steadily rising temperatures have created longer, warmer, and drier summers for some time. This heated climate accelerates mosquito reproduction. Mosquitoes are the primary vector for heartworm disease, and large populations put pets at higher risk, since only one bite is necessary to transmit Dirofilaria immitis, the organism that causes heartworm disease.
  • Increased pet transport — Over the past 10 years, more dogs and cats have been  imported to the PNW. Many come from heartworm-endemic regions, and knowingly or unknowingly, organizations are introducing heartworm disease to our area and exposing local pets to a previously rare to nonexistent threat. 
  • Unprotected pets — Historically, PNW pets were less likely to be prescribed or receive heartworm prevention. And, because modern pet owners may not be aware of this rising health risk, many dogs and cats are vulnerable to infection and contributing to the sharp rise in cases.

The vicious cycle—how heartworm disease affects pets

Heartworm disease is spread by infected mosquitoes that act as a vector between infected and uninfected pets—collecting or injecting Dirofilaria immitis through the bite wound each time they take a blood meal.

Once inside the pet, juvenile heartworms (i.e., microfilariae) slowly migrate from the tissues, to general circulation, to the lungs and heart, where they create a cascade of inflammation and irreversible damage. If a pet is left untreated, the adult heartworms, which can grow to 12 to 14 inches, can cause life-threatening cardiovascular complications in dogs and cats.

How will I know?—heartworm disease signs in pets

Because heartworm disease progresses slowly, dogs do not show visible signs until they are severely affected, which can be six or more months after infection. Worse, cats—who are not considered natural hosts for the disease—may show no signs at all. Clinical signs may include:

  • Dogs:
    • Persistent cough
    • Exercise intolerance
    • Fatigue
    • Weight loss
    • Distended abdomen
  • Cats:
    • Coughing or wheezing
    • Asthma attack-like respiratory distress
    • Intermittent vomiting
    • Loss of coordination
    • Seizures
    • Sudden death

Positive is negative—heartworm treatment for pets

Although heartworm disease is treatable for dogs, the process is lengthy, tenuous, and expensive (i.e., $1,000 on average). And, despite treatment, many dogs suffer life-long side effects because of their damaged heart muscle and large lung vessels.

Unfortunately, no safe treatment—only supportive care—is available for cats with heartworms, which makes prevention an absolute necessity. 

Protect your pet—heartworm prevention strategies

A vet in a red uniform draws blood from the leg of a small black and white dog using a syringe. The dog stands on a white examination table, and the veterinarian's stethoscope is visible.

Heartworm disease is easier, safer, and more economical to prevent than to treat. And now that you know the real and rising threat, team up with Village Veterinary Hospital to protect your pet. 

  • Get tested — First, let us test your pet for heartworm disease. This simple blood test takes only 10 minutes and can detect the presence of adult heartworms. We may also need to screen your pet’s sample for immature microfilariae. If your pet tests negative, we’ll help determine the best prevention product for you and your pet. If the result is positive, we’ll discuss treatment or management options.
  • Year-round prevention — All dogs and cats should receive year-round heartworm prevention, including indoor-only pets, as mosquitoes can easily enter basements and garages, and overwinter in a dark, quiet corner of your home. Oral, topical, and injectable prevention products are simple, safe, and incredibly effective against this encroaching threat. Because mosquitoes must bite a pet to establish infection, all prevention types work retroactively to eliminate immature microfilariae in their earliest stage, after the pet is technically “infected” but long before the parasites can migrate, mature, and cause life-threatening harm.
  • Annual testing — Once we have established your pet’s heartworm prevention plan, we recommend annual heartworm testing for dogs to ensure the prevention is working as intended, and no break-through infection has occurred. Because feline heartworm disease behaves differently, cats on preventives require only intermittent testing.
  • Adopting? Ask for paperwork — If you’re adopting a dog or a cat from a shelter or rescue, request proof of a recent heartworm test and a completed health certificate. If these documents cannot be provided, consider looking elsewhere for a pet.

After many years as merely a distant threat, heartworm disease has arrived in the Pacific Northwest, and rising temperatures and increased pet travel from endemic areas mean the disease is here to stay. Don’t ignore this growing danger—take action today to protect your dog or cat. Schedule an appointment for your pet’s exam, heartworm testing, and prevention plan at Village Veterinary Hospital.