Heartworms In Dogs: Symptoms, What Causes, Test, Prevention, Medicines, Shot & Cost

One of the things you should be afraid of as a dog owner is a heartworm. Sadly, when the disease is already at its advanced stage, the symptoms appear. The purpose of this article is to educate dog owners like you about this life-threatening dog disease so that you can take the required preventive steps on your canine buddy to prevent heart disease.

What is Canine Heartworm?

This is an infection caused by a bite of a mosquito. Yes, it’s true. An apparently small and harmless insect may actually present your dog with a serious health problem. These worms are very harmful because they do not invade the intestinal lining, but they attack the key organs in your dog’s lungs that are the heart and the blood vessels.

If your dog is diagnosed with heartworm disease, this implies it has been infected with an organism called Dirofilaria immitis, a nematode or a roundworm known as heartworm for its name. The severity of this disease relies on variables such as the number of heartworms detected in the body of your dog, how long these worms have been lurking inside, and your dog’s reaction to these worms.

What Causes Heartworms Disease in Your Dogs ?

Perhaps you’re wondering how a small mosquito can attack your dog when it’s covered with fur/coat. But this sort of mosquito is microscopic and can, therefore, enter the skin of the dog irrespective of the type of dog coat. So whether your dog is a chihuahua or a Siberian husky, heartworm infection can still infect them.

Once your dog is bitten by a mosquito which carries the nematode Direfilaria immitis larvae, the worms invade your dog’s body. The larvae travel around the body of your dog until it settles in the heart and the blood vessels of your dog’s lungs.

The larvae mature in the heart of the dog and the lungs ‘ blood vessels. These rise to about 12 inches in size once the heartworms achieve maturity. The worrying aspect is that these heartworms keep multiplying and releasing undeveloped heartworms in your dog’s bloodstream called microfilariae.

But this process takes time, about six months to a year, and that is precisely why the heartworm infection is already at its advanced stage at the moment the symptoms manifest. It’s like that when your dog is diagnosed, the heartworms have multiplied into a hundred or so.

Now when a mosquito bites the infected dog, this microfilariae enter the mosquito’s body and then passes the disease to another dog. Such is the heartworm life cycle and avoidance is something that all fur parents need to think seriously about. I will discuss it later in this article.

Which Dogs Are Prone To Get Heartworm Disease?

Although all dogs have the risk to get this infection, there are those who have higher chances of getting infected and these are the following:

  • Dogs which are not administered with heartworm preventive medicines.
  • Dogs which live in mosquito-infected areas.
  • Dogs which live in endemic regions, meaning, there is a high incidence of heartworm disease in that particular region.
  • Dogs that live in warmer regions.

Ways To Determine If Your Dog Is A Carrier of This Disease? (Signs)

Below are the different levels or classes of heartworm canine disease:

1. Class I:

At this time,  a dog does not show any indications that it has been affected by heartworm disease. It is asymptomatic except for occasional mild coughing. This is the stage when the worms are getting its way into a dog’s heart.

The reason there are no apparent indications is that the heartworms have not yet replicated and the underdeveloped larvae called microfilariae have not been produced. Moreover, the dog’s body is not yet producing any antigens to combat infection. 

2.  Class II:

This is the stage where the dog starts to show visible signs of heartworm disease. The usual symptoms in this stage are coughing and getting tired too easily.

There may be already the presence of microfilariae. The dog’s body starts to produce antigen to battle the infection.  A blood test can already pinpoint that the dog is infected with heartworm disease.

3.  Class III:

At this third stage, the advanced symptoms are already manifesting. These symptoms include weight loss, a cough that has deteriorated and may have some blood, labored breathing, dry or greasy hair, potbelly, and low stamina for exercise.

At this stage, x-ray examination shows that a dog is suffering from heartworm infection.

4.  Class IV:

This advanced stage is more centered on providing convenience medications. The dog can no longer survive at this point because a multitude of heartworms, a condition known as caval syndrome, are already present.

Summary of Symptoms of Heartworms in Dogs:

  1. Dry Cough
  2. Inability to Exercise or Lethargy
  3. Weight Loss
  4. Difficulty in Breathing
  5. Chest is Bulging
  6. Allergies
  7. Collapse
  8. Nose Bleeding
  9. Pneumonia
  10. Sleeping Too Much
  11. Increase in Blood Pressure
  12. Blindness

Heartworm Tests for Dogs:

This is a silent killer since the signs are seen at the advanced stage. That’s why it’s suggested that you test your dog regularly. Even if you live in colder climates such as Alaska, undergoing heartworm tests is still a good practice. Remember the dog is asymptomatic during the initial stage of this disease. Or if ever there is a symptom, most of the time, these are mistaken for another type of dog health problem.

How Testing is Done?

A blood test is a proven way to determine if your dog has heartworm disease. There are two ways that the Vet can do after getting a sample of blood from your dog. It could either be:

1. Antigen Test: This will determine the presence of female heartworms in the bloodstream of your dog.

2. Microfilaria Test: This type of a blood test is done in order to find out if the larvae have multiplied and have produced the underdeveloped heartworms referred to as microfilariae.

Both of these blood tests are very precise, and even if the disease is at its earlier stage it can be detected. Now if the blood test reveals positive results, the vet does further heartworm testing to find out how bad the infection is. 

These additional tests are:

3.  X-ray: To find-out the shape as well as the size of the heart. Dogs with an advanced stage of heartworm have enlarged pulmonary arteries.

4.  Ultrasound:  This is done to find out the condition and if the heart is functioning in a normal way or not. Also, to determine which stage is the heartworm disease.

In short, a simple blood test is a sure-fire way to determine if your dog is infected or not. Therefore, do not postpone and perform this test on a yearly basis to inhibit the progression of heartworm disease. As I said earlier, during the early stages, the symptoms are not seen. The duration of inoculation is quite long once an infected mosquito has bitten your dog. It will take an average of six months before you see any signs. But a blood test can immediately detect signs so don’t think twice about doing the heartworm blood test.

Heartworm Preventive for Dogs:

Prevention is the best way to stop your dog from getting infected. I will share with you two types of canine heartworm prevention:

1. The Conventional Method to Prevent Canine Heartworm:

You can avail of the monthly chewable tablets for the prevention of heartworm. Most dogs are okay with the chewable tablets as these come in the form of a treat. But you have to be consistent like you have to administer it to your dog every month on the same day to be very effective.

On the other hand, you have another option, which is the topical medication, if you don’t want this approach. This is a liquid that will be applied to your dog’s skin. This is the best option if you find it challenging to let your dog ‘ swallow the bitter pill.’ However, if your dog is hyperactive, it can be quite messy due to the liquid medication.

2. The Natural Method to Prevent Canine Heartworm:

By removing stagnant water around your backyard, you can reduce the population of mosquito in your home. You can also plant mosquito repellants such as marigold, sage, and catnip in your garden.

You can install insect screens in your windows to stop the mosquito from going inside your home.

Try to minimize the use of chemical mosquito repellants as they are harmful to your pets as well. Instead, attempt to mix water, 25 drops of eucalyptus oil and two ounces of coconut oil or almond oil. Sprinkle this combination on your dog’s coat but be sure to prevent the regions of the eye and nose.

Heartworm Medicines for Dogs (Preventive Medicines):

Listed below are the different kinds of heartworm meds for dogs. Take note that these are all prescriptive medicines:

1. Ivermectin-Based Medicines :

  • Heartgard Plus Brand: This is widely used medicine because it is a fusion of Ivermectin and Pyrantel. Your dog will love the beefy flavor of this medicine.
  • Interceptor Plus Brand: Aside from treating heartworms, this chicken-flavored medicine also kills tapeworm and whipworm in dogs. 
  • Tri-Heart Plus Brand: The price of this brand medicine for the treatment of heartworm is much lower than the Heartgard plus but it gives the same results.

2.  Selamectin-Based Topical Medicines:

3.  Moxidectin-Based Topical Medicines:

  • Advantage Multi Brand: This is an easy to apply topical treatment for heartworm, fleas, hookworms, and other parasites in dogs.

Heartworm Shot for Dogs (Preventive):

If you don’t like giving your dog a pill once a month or applying topical medication, the best option is the heartworm shot. Administered this twice a year. The only heartworm shot for dogs approved by the FDA is the ProHeart 6 brand with Moxidectin’s generic name.

What Medicine is Used to Treat Heartworm?

If your dog is positive with this disease, a very expensive medicine called Immiticide is administered in a cycle of three injections. Antibiotics like Doxycycline is also given along with Prednisone.

Heartworm Treatment Cost:

Once the heartworm infection is positive for your dog, be prepared to spend a lot of money. It might be between $400.00 and $1,000.00 or so. The cost depends on your dog’s size, weight and the stage or severity of the infection.

The reasons why it is so expensive is because of the following factors:

  • Diagnostic Testing like blood testing and x-ray
  • Regular Vet Visits
  • Hospitalization
  • Immiticide is the drug used to treat the advanced stage of heartworm, not easy to procure, thus, it fetches a high price.

BUT, if you’re only going to use preventive drugs like Heartgard Plus, you’re only going to spend about $5 to $15 a month. For three months, topical medicine such as Revolution will cost you between $50.00 and $100.00 only. The dosage is relative to your dog’s weight.


Heartworm is deadly. The sad fact about this dog disease is that the symptoms are only seen once the disease has advanced. But there is something you can do about it. Make use of preventive drugs that can save your dog’s life. Moreover, the cost of preventive drugs and heartworm treatment in dogs is very significant. Act now before it’s too late — give your dog the preventive medications that could prevent heartworm infestation.

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