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Preventing Heartworms in Dogs

Causes of Heartworms in Dogs, Prevention, and the Symptoms

Updated on February 03, 2023
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Reviewed by Dr. Whitney Miller
DVM, MBA, DACVPM

What are Heartworms? | Heartworm Prevention | Heartworm Awareness | How do I know if my dog has heartworms?

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As a loving, responsible pet parent, you want your dog to be healthy and protected from parasites. Even the idea of parasites is enough to make one’s skin crawl.

When many people think of pet parasites, they typically think of fleas & ticks. While you can learn more about fleas in our guide A Dog Fight Against Infestation, some parasites can be even more life-threatening. 

Another common and important parasite for pet parents to be keenly aware of is heartworms. Heartworm infection is serious business. It can lead to lasting health problems for your dog and even premature death.

However, armed with knowledge about the signs of heartworms in dogs and year-round prevention, you can help your pup avoid these deadly parasites. Let’s explore what heartworms are, what causes heartworms in dogs and what you can do to prevent them.

What are Heartworms

Heartworms (Dirofilaria immitis) are thread-like parasitic worms. They’re spread by mosquitoes while still in their larval stage, and they typically infect the heart, lungs and other associated blood vessels of the hosts they invade.

Once established in a host, they mature into adults, mate and produce offspring. They can then further infect the host or potentially be carried by mosquitos to other hosts—maybe even your neighbors’ pets.

Adult heartworms—which look like cooked spaghetti—can live 5–7 years and reach a length of 9–12 inches. It is easy to understand why a buildup of such large worms could affect heart function and put your pet at risk.

Some of heartworms’ favorite hosts are canines—including wolves, coyotes and foxes. They even like more distantly related animals, such as ferrets, cats and sea lions. Heartworms can move from these wild populations to infect domestic animals, too.

If you’re not familiar with these parasites and haven’t seen heartworm symptoms in dogs, it’s understandable. In the United States, they are most common along the Atlantic and Gulf Coasts, the full length of the Mississippi River and everything in between. Not coincidentally, these areas of the United States also have the highest concentration of mosquitos. 

Even so, cases of heartworms in dogs are reported every year in all 50 states; to help your pet avoid this life-threatening disease, you must to protect your pet year-round and familiarize yourself with heartworm disease. By learning ways to prevent infection, you can help make heartworms less worrisome.

golden lab

How to prioritize heartworm prevention for dogs

If an ounce of prevention is worth a pound of cure, this is especially true for parasitic infections like heartworms in dogs.  

Once heartworms have taken root in your dog, treatment also has risks and is time-consuming and more costly than a lifetime of prevention. Even after they are removed, the presence of heartworms can have lasting effects on your pets. For this reason, prevention is vitally important.

Luckily, your veterinarian can offer you many options for heartworm prevention to fit your dog’s temperament and lifestyle. These can include: 

  • Pills 
  • Chewables 
  • Topicals 
  • Injections 

Preventives for heartworms in dogs need to be prescribed by your veterinarian and administered to your pet on a regular basis, often monthly, but some newer options are administered every 6 or 12 months. They are all simple and budget friendly, no matter which form you choose, and many also protect against other potential parasites, such as roundworms and hookworms. Some newer prevention options also give you flea & tick prevention in one medication.

Heartgard Plus

Simparica Trio

Revolution

Interceptor Plus

In all cases, heartworm prevention for dogs is key. It’s possible to cure a dog of an infestation of adult heartworms, but the process is time-consuming, costly and can come with uncomfortable side effects. The typical treatment requires hospitalization while receiving injections of medicine to kill adult heartworm, along with several weeks or months of limited exercise. Consulting your veterinarian will help you determine the appropriate course of action as there are other potential side effects of heartworm treatment. 

Natural or over-the-counter medications are not recommended because they are not effective forms of prevention. Methods to keep mosquitos off your dog can help but are only recommended in addition to heartworm prevention medication. It only takes one bite from a mosquito carrying heartworm disease to infect your dog. Holistic solutions are also not recommended to prevent the signs of heartworms in dogs. Prescription prevention is the only way to give your dog the best protection.

Important aspects of heartworm prevention include: 

  • Keep your dog, cat and ferret on year-round prevention
  • Consult with your vet regularly to understand the risk in your area and determine additional preventive measures 
  • Be consistent and on time with their heartworm medication 
  • Consistently test for heartworm disease annually (as recommended by the American Heartworm Society)

Some pet parents might assume dogs don’t need protection during the winter months, but it’s best to continue prevention year-round to guard against an accidental lapse in protection. Most heartworm prevention medications work by treating heartworms your pet has already been exposed to, so any break in prevention can put your pet at risk, even if you haven’t seen any mosquitoes recently. The American Heartworm Society also recommends year-round prevention.

dog and vet

Why heartworm awareness is important?

Heartworm infection is a big deal. Like any parasite, heartworms slowly deplete the host from the inside out. Heartworm disease can lead to lung disease, heart failure, organ damage and even death. 

The American Heartworm Society estimates that more than a million dogs in the U.S. have heartworm disease. Don’t let your pet be one.

If heartworms become established, they can cause lasting damage to any part of the host they become attached to—particularly the heart, lungs and primary arteries. Many pets will ultimately go into heart failure. An infection can be difficult and costly to bring under control. Once heartworms reproduce, they can also infect other organs and the muscle tissue of your dog. This also carries the risk that mosquitoes will bite your infected pet and spread heartworms to other pets in the area.

Even after the worms are gone, it may take time for your pup to recover. Some pets never make a full recovery. 

For these reasons, it’s important to see prevention as the ideal method for heartworm control.

How do I know if my dog has heartworms?

There is no way to look at your dog and tell if they have been exposed to heartworms, so regular checkups with your veterinarian are critical. Signs of heartworms in dogs aren’t always obvious or easy to spot either, even if your dog is sick.

A persistent cough—particularly during exercise—is a classic sign, although not always a perfect giveaway. If you do notice a cough combined with a lack of energy when running or playing, your pet may be experiencing heartworm infection.

Other heartworm symptoms in dogs include:  

  • Lower energy levels 
  • Lethargy 
  • Changes in appetite 
  • Weight loss 
  • Breathing difficulties 
  • Asthmatic symptoms 
  • Fainting or collapsing 
  • Distended belly
  • Increased drinking or urination

While these are some of the most common signs of heartworms in dogs, you should never self-diagnose your pet without seeing your veterinarian. It can be easy to confuse these symptoms with other ailments. If you notice any abnormal behavior in your pet, schedule an appointment with your veterinarian. They will administer blood tests and examinations to help them make a correct diagnosis. From here, they will advise you on the appropriate treatment plan for your pet.

Now that you’re armed with the knowledge of what causes heartworm in dogs, what the symptoms are and how to help prevent heartworms, you can help your pup stand a better chance of avoiding these parasites altogether. However, the battle against infestations doesn’t stop there—take the time to learn about other pests that can be harmful to your dog. Fleas, ticks, hookworms and tapeworms can cause diseases that can be prevented with attention, knowledge and the right preventive measures. 

At Petco, our online Resource Center has helpful guides—like How Flea Treatments Work—that can help you on your journey to becoming your pet’s trusted health & wellness supporter. 

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