Yellow Labrador Retriever looking to the right side in the grass.

Heartworm disease is a serious illness carried by mosquitos that are common in certain parts of the United States.

Heartworm in Labs can cause catastrophic sickness and eventual death for your pet, if not treated or prevented.

Surviving heartworm disease is not guaranteed, and the treatment isn’t easy on your dog. It won’t be easy on you watching your pet go through it, either.

Heartworm in Labs is expensive, complicated, and difficult to treat.

This is especially true for active, athletic breeds such as the Labrador Retriever, which can have a difficult time managing the stringent activity restrictions during the active treatment phase of heartworm disease.

As with other conditions, prevention is the best method of making sure your Labrador does not become heartworm-positive.

So what is heartworm in Labs? And what can you do about it as a dog owner and Labrador lover?

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In this article, we’ll go over the basics of heartworm disease in dogs: what causes it, how it’s diagnosed, and what the treatment options are.

We’ll also cover what to discuss with your veterinarian regarding preventive methods that they can offer you to help keep your Labrador safe from heartworm disease.

Read on to learn all about heartworm in Labs, and how to keep your pet safe!

Heartworm in Labs – How to Keep Your Dog Safe from Heartworm Disease

What is Heartworm in Labs?

Heartworm is a serious disease in dogs that can cause multiple organ failure, including heart failure.

Worms are spread to your dog through the bite of an infected mosquito. These worms, which at maturity resemble strands of spaghetti, then take hold inside your dog’s body, where the dog becomes the host.

The worms mature and reproduce inside your dog, and then wreak havoc on your dog’s internal organs.

This will lead to a very unhappy Labrador and a very concerned owner.

Developed heartworms resemble strands of spaghetti throughout your dog’s heart and other organs, reaching up to 12 inches in length if left untreated over many years.

Heartworm is diagnosed through a blood test performed by your veterinarian at their office. If the initial results show a preliminary positive result, your vet will likely repeat the test and send it out to a lab for even further testing.

Other dogs cannot catch heartworm from an infected dog, nor can humans. The mosquito is the real risk to your dog as a source of infection.

For this reason, areas with a higher prevalence of mosquito populations in warmer climates (such as the southern United States) have dramatically higher rates of heartworm disease.

If you’re a pet owner in the United States, especially in the south, please pay attention to your pet’s risk of heartworm disease!

If you’re curious about more in-depth details on the science behind the disease, check out this guide from the FDA regarding the heartworm lifecycle in dogs.

Dogs aren’t the only animals at risk for heartworm, either. It can also affect cats and ferrets.

Black Lab lying down on bench looking tired. Fatigue is a common symptom of heartworm in dogs.

It takes approximately 6 months for a dog to test positive for heartworm after they have been bitten by an infected mosquito.

If you adopt a new dog from a shelter or a rescue, they will likely perform a test to find out before adoption if the animal is heartworm-positive.

However, since it takes 6 months after being bitten by a mosquito for a dog to show a positive test, you will be asked to repeat the blood test, later on, to confirm that your dog is truly negative.

We’re going to share more about our Labrador’s experience with this in just a bit.

This 6 month period of re-testing is why it’s important for regular checks with your veterinarian, as well as preventive medication, which we’ll discuss further below.

Why is Heartworm in Labs a Serious Illness?

Heartworm in Labs can cause damage to your dog’s heart and internal organs, and can eventually kill your dog if left untreated.

You may be completely unaware if your Labrador is heartworm-positive, because there may be no outward signs or symptoms of heartworm in dogs, especially in the earliest stages.

Later on, as the disease progresses, there may be symptoms such as coughing, being overly tired, and trouble breathing.

In the advanced stages of heartworm disease, your dog may suffer from blockages in the heart and heart failure. At this point, treatment may be very difficult and not result in the best outcome for your dog, which is tragic.

That’s why it’s critical you have your Labrador tested by your veterinarian on a regular basis.

It’s also important that you discuss preventive medication with your veterinarian as soon as your dog joins your family.

What Areas of the United States Have Heartworm in Labs?

According to the American Heartworm Society, veterinarians have treated heartworm in all 50 states.

However, the biggest hotspots of the country are the South and Gulf Coast regions.

The top five states in the US for cases are:

  • Mississippi
  • Louisiana
  • South Carolina
  • Arkansas
  • Alabama

That’s why it’s especially critical that you discuss heartworm prevention with your veterinarian, especially if you’re a resident of the listed states above.

You can also take a look at this map from the American Heartworm Society to see the prevalence of cases where you live.

Even if you’re not in the southern US, ask your veterinarian about the prevalence of heartworm in your area, and what they recommend.

Surviving Heartworm – A Lab Rescue Story

We adopted a wonderful rescue Labrador who’d been found abandoned in Georgia, another state with extremely humid weather and the large presence of mosquitos throughout a good portion of the year.

Our beloved rescue Lab initially tested negative for heartworm upon adoption, and we were relieved. According to our vet’s recommendation, he was started immediately on preventive medication.

But since it can take 6 months for the heartworm blood test to show a past positive exposure, we had him tested again half a year later.

Photo of chocolate Labrador who survived heartworm in dogs.

Six months later, when he had his follow-up test, he was heartworm-positive, which was shocking, and devastating for such an active, energetic Labrador.

You would never have known he was heartworm-positive from the way he was acting, and he had no outward symptoms.

He went through 90 days of very difficult treatment, but we were fortunate that it was caught early and he was able to recover.

We’ll talk more about what the treatment entails in a moment, but we were required to keep him very quiet, calm, and subdued for 90 days.

Lab parents, you know how hard keeping your dog calm for one day would be, so imagine 90 days in a row… it was pretty stressful for everyone, including the Lab.

That’s why it’s critical you stay vigilant and follow your vet’s guidelines for regular testing and preventive methods.

This brings us to another very important next section, prevention!

What Can I Do to Prevent Heartworm in Labs?

Talk with your veterinarian about the options available for you to prevent heartworm disease from occurring.

You can help prevent heartworm in Labs by giving your dog a prescription medication on a monthly basis. These medications work by killing any larvae that may be present in your dog’s system before they have a chance to mature, reproduce, and cause significant harm to your dog.

Your veterinarian is the best resource for you in helping to prevent heartworm.

We have, and have always had, all of our Labradors on monthly preventive medication to prevent heartworm disease.

Common brands of preventive medication include Heartgard, Trifexis, Interceptor, and Tri-Heart Plus.

The average cost for preventive medication for a Labrador weighing approximately 60-80 lbs is about $9/month. But the cost of treating heartworm in dogs can be thousands of dollars, so we consider the cost of preventive meds money well-spent.

You can purchase them monthly or in a 6 or 12-month package, which is a little bit less expensive and will help make sure you don’t run out.

Tip: If you have a Costco membership, you can get some of these brands through their pharmacy, and save yourself even more money. You’ll still need a prescription from your vet.

Several of these products also can prevent hookworm and other types of worms, in addition to heartworm in dogs.

These medications are only available by prescription from your veterinarian.

This is because your vet needs to perform a heartworm blood test on your dog before administering preventive medication.

At Labrador Wise, our Labs are on Heartgard all year round and have a veterinarian-administered test once a year to confirm they still remain negative.

One other tip we learned from our vet: you might be wondering why our rescue Lab was positive even though he was on preventive medication from the day we adopted him (we wondered the same thing when it happened).

Wouldn’t the medication have killed any larvae in his body when we started him on it?

Our vet explained that the medication only works backward 30 days in killing the larvae present in your dog, so if your dog was already exposed a while in the past before you rescue or adopt them (for example, 3-4 months before), it wouldn’t be able to kill the larvae that had progressed that far ahead.

That’s why heartworm medication is given monthly because to skip a month would mean your pet is unprotected.

Our rescue boy must have been infected a few months before he was rescued (by our amazing friends at Labrador Retriever Rescue of Florida) and became a part of our family.

White Labrador puppy sitting in grass.

My Dog Is Heartworm-Positive. What Will Treatment Be Like?

Treatment of heartworm in Labs can be intense and stressful. It can also be extremely expensive.

Our heartworm-positive Labrador had vet costs of over $1000 for treatment lasting 90 days.

It was a very difficult and challenging treatment to go through, even with a cooperative, friendly dog like a Labrador.

The treatment of heartworm disease in your dog will take several important steps:

  1. Your veterinarian will likely re-test to confirm the positive result. This may take a few days for the confirmed results to return.
  2. Your Labrador will immediately be placed on “bed rest” or “crate rest,” and their activity level and exercise will be dramatically reduced. THIS WILL CONTINUE FOR THE DURATION OF THEIR TREATMENT, WHICH CAN LAST UP TO 90 DAYS.
  3. You will be cautioned not to allow your dog to have any activity: no walks, no games of fetch, NO PLAYING. This can be really hard to do with an active Labrador Retriever.
  4. Your veterinarian will create a treatment plan for your specific dog, which may require additional testing on your Labrador’s heart and other organs to determine the extent of the disease.
  5. A medication will be administered to your dog on a frequent basis to kill the existing heartworms inside your dog’s body. In our case, it was an arsenic-type treatment.
  6. You will return to your vet every 30 days (or more frequently, depending on severity) for continued doses of this treatment for your Labrador.
  7. After approximately 90 days, your Labrador will be considered treated, but not cleared. They can begin to resume normal activity levels.
  8. After 6-9 months, your veterinarian will order another heartworm test to confirm that the treatment was successful.

As you can see, treatment of heartworm in Labs is challenging and very difficult.

As Labrador owners know, Labs are very active dogs. It is very hard to keep an energetic, athletic Labrador crated, restricted from most exercise and forbidden from any kind of activity for 90 days.

No playing fetch, no dog parks, no walking in the neighborhood.

No swimming, no car rides (other than crated to the vet’s office), no rolling around on the floor with new toys, and definitely no playing with kids or other dogs.

You will be cautioned by your vet to not allow your dog’s heart rate to rise during treatment, and to keep your Lab calm at all times.

These treatment restrictions can be very stressful to implement and uphold for any dog, especially active large breeds such as Labrador Retrievers.

Summary – Heartworm in Labs

If your Labrador tests positive for heartworm, it will be a very difficult and stressful experience for both of you.

We hope that you never have to experience heartworm disease in dogs, and encourage you to work with your veterinarian to make sure your dog is protected.

Have you had first-hand experience with heartworm in dogs? Let us know how you handled it in the comments below.

And if you’re just learning about the world of Labradors, check out our Puppy Guide or our Health & Care section for more helpful tips on Labrador life.

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  1. My 3 year old lab is being treated ( slow kill) using at first Advantage multi… now my vet has recommended treating with heart guard… ivermectin/ pyrantel. I am concerned about how long this has taken… she was tested positive when I adopted her in October of 2021… yesterday April 11 she tested positive again after all the advantage multi treatments…so in may I will give her the new chewable med… and hope for best outcome

    1. Hoping for a good outcome for your beloved Lab! Sending you (and her) best wishes for successful healing.

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