Why Every Dog Needs Protection

August in the Tobacco Valley is high summer at its finest. The days are long and warm, the evening light paints the Whitefish Range in shades of gold and amber, and if you sit outside after dark, you’ll hear the familiar hum of mosquitoes rising from the Tobacco River bottoms, irrigation ditches, and the quiet backwaters of Lake Koocanusa.

For most of us, mosquitoes are simply part of summer—a nuisance that calls for a quick swat or a little bug spray. For our dogs, however, a single mosquito bite can carry something far more serious: heartworm disease.

At Mountain Vista Veterinary Services, we frequently hear, “I thought heartworm was only a problem in the South.” It’s a common misconception, but unfortunately, it isn’t true. While Montana has historically had fewer cases than many southern states, heartworm is becoming more common across the state, and August—when mosquito activity reaches its peak—is the perfect time to make sure your pet is protected.

Why Heartworm Is Becoming More Common in Montana

The Companion Animal Parasite Council (CAPC) identifies Montana as an area of increasing heartworm risk. Western Montana, including the Flathead Valley and Tobacco Valley, has seen growing concern due to several factors:

  • Longer, warmer summers that extend mosquito season.
  • Increased movement of dogs from regions where heartworm is common through rescue organizations, military relocations, and seasonal travel.
  • Wild canids, including coyotes, that serve as natural reservoirs for the disease.

Here in northwest Montana, mosquito populations are often at their highest from late June through August. Areas around the Tobacco River, Lake Koocanusa, irrigation canals, ponds, and standing water provide ideal breeding conditions. Even though our overall risk remains lower than many parts of the country, it only takes one infected mosquito to transmit heartworm to an unprotected dog.

How Dogs Get Heartworm

Heartworm disease begins when an infected mosquito bites a dog.

The mosquito deposits microscopic heartworm larvae beneath the dog’s skin. Over the next several months, those larvae migrate through the body until they reach the heart and pulmonary arteries, where they mature into adult worms.

Adult heartworms can grow to nearly twelve inches long and live for five to seven years. As they accumulate, they interfere with normal blood flow, damage blood vessels, strain the heart, and eventually lead to serious lung disease, heart failure, and damage to other organs.

The important takeaway isn’t the complicated biology—it’s this:

A single mosquito bite has the potential to begin a disease that can become life-threatening years later.

Does Montana’s Winter Eliminate the Risk?

Many pet owners assume our long winters naturally protect dogs from heartworm.

While mosquitoes are inactive during freezing weather, Montana summers provide more than enough warm days for heartworm transmission. The parasite develops inside mosquitoes whenever temperatures remain consistently warm, something we regularly experience throughout June, July, and August.

Mosquitoes may also survive longer in protected environments such as garages, barns, sheds, and livestock facilities, extending exposure beyond what outdoor temperatures alone might suggest.

For these reasons, the American Heartworm Society recommends year-round heartworm prevention for all dogs, regardless of where they live. We support that recommendation because prevention provides continuous protection without requiring owners to guess when mosquito season begins or ends.

The Good News: Heartworm Disease Is Almost Entirely Preventable

This is one of the easiest diseases we can prevent.

Monthly heartworm preventatives—available as tasty oral chews or topical medications—eliminate immature heartworm larvae before they have the opportunity to mature into adults.

Many products also protect against intestinal parasites and, depending on the product, fleas and ticks as well.

For families who prefer not to remember a monthly medication, injectable heartworm prevention administered by your veterinarian every six or twelve months can be an excellent option.

The key is consistency.

Missing even one monthly dose during mosquito season can leave your dog vulnerable.

If you’re unsure which prevention program is best for your pet, our team is happy to help you choose the safest and most effective option.

Why Prevention Is Better Than Treatment

Heartworm treatment is significantly more difficult than prevention.

Once adult heartworms are established, treatment involves multiple deep intramuscular injections of melarsomine, an arsenic-derived medication specifically designed to kill adult worms.

During treatment, dogs must remain on strict exercise restriction—often requiring crate rest—for several weeks because dead worms can create dangerous blockages in the lungs as they break down.

For energetic dogs, this period of restricted activity is often the hardest part of treatment for both pets and owners.

Treatment also comes with risks, potential side effects, and costs that can easily reach several thousand dollars.

By comparison, a full year of prevention typically costs less than one hundred dollars.

The difference is clear:

Preventing heartworm is safer, easier, less stressful, and far less expensive than treating it.

Why Annual Heartworm Testing Matters

Even dogs taking preventative medication should receive annual heartworm testing.

A simple blood test detects proteins produced by adult female heartworms before clinical signs become obvious.

Testing confirms that your prevention program is working and helps identify infections early, when treatment has the best chance for success.

Testing is especially important if:

  • You’ve recently adopted a rescue dog.
  • Your dog has ever missed preventative doses.
  • You’re unsure of your dog’s prevention history.
  • Your dog previously lived in another state.

Frequently Asked Questions

Can dogs get heartworm in Montana?

Yes. Although heartworm is less common here than in many southern states, infected mosquitoes are present in Montana, and local dogs can become infected.

Can indoor dogs get heartworm?

Absolutely. Mosquitoes frequently enter homes, garages, and other buildings. Even dogs that spend most of their time indoors remain at risk.

Do puppies need heartworm prevention?

Yes. Puppies should begin heartworm prevention at the appropriate age recommended by their veterinarian. We can help determine the best schedule for your puppy.

Is heartworm contagious between dogs?

No. Dogs cannot transmit heartworm directly to one another. The disease is spread only through the bite of an infected mosquito.

Protect Your Dog Before Mosquito Season Protects the Mosquitoes

As mosquitoes rise from the Tobacco River bottoms during these warm summer evenings, now is the time to make sure your dog is protected.

If your pet is due for heartworm testing, needs a refill on preventative medication, or you’re unsure which product is right for your family, we’d be happy to help.

Preventive medicine is most rewarding when we stop disease before it starts—and heartworm is one of the best examples of that philosophy.

Contact Mountain Vista Veterinary Services to schedule your dog’s annual wellness exam and heartworm test.

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