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Dog Heartworm Facts And Fiction

How to prevent your dog from getting heartworm and how to treat it if it does get infected. We’ll cover heartworm symptoms, heartworm treatments, and a full FAQ to answer all your questions about dog heartworm.

If you’ve ever seen the movie Jungle, then you have seen with your own eyes some of the more disturbing nematode behaviors. I can’t even imagine having to pull out a worm from a wound.  Now imagine the worm is living in and around your heart. Well, that’s what dogs have to face with dog heartworm.

What Heartworms Are

Dog Heartworm or Dirofilaria immitis is a parasite that infects dogs and can be deadly.  D.immitis is a type of roundworm, also known as a nematode. These nasty little creatures comprise a family of approximately 25,000 species. Nematodes are found all across the planet and in multiple environments.  They have a digestive system that typically has an opening at both ends, and is basically tubular in shape.

The heartworm is a parasitic organism.  That means that it uses a host as a means of food and shelter while doing some harm to the host.  They have evolved specifically to do so and have no choice in the matter at all. Can you imagine what their existence is?  Trapped as an organism that lives inside another and slowly kills it. But we’ll get into all the lovely details soon.  We’ll also talk about the heartworm symptoms so you know what to look for.

Where Dog Heartworm Is Found 

D.immitis is found where the mosquito which carries it is found. Dog heartworm has been identified in all 50 states of the United States of America.  It also exists across Europe and Asia as well. So basically it’s all over the place. 

How Dogs Get Infected

Dogs get heartworm from an infected mosquito.  The mosquito transmits the larvae to the dog’s subcutaneous skin.  From here, the larvae grow and sheds. This transformation changes it into its final stage of life and it works its way into the muscles of the chest and abdomen.  

Wait (record scratches, music stops) did I just say the final stage of life?

Life Cycle Of Dog Heartworm
Life Cycle Of Dog Heartworm

Image Source: By Cú Faoil (text), Anka FriedrichDirecoes_anatomicas.svg: RhcastilhosMosquito gender en.svg: LadyofHatsderivative work: Anka Friedrich – Own workThis file was derived from Dog tan.svg: Direcoes anatomicas.svg: Mosquito female.svg:Mosquito gender en.svg:, CC BY-SA 3.0,

As mentioned above, dogs get heartworm from mosquitoes.  So let’s dive into these bugs for a change as they like to dive into us, so to speak.

Mosquito Facts

  • There are over 3000 species of mosquito.
  • Mosquitoes can live from 2 weeks to 6 months.
  • Three types of Mosquito are responsible for the majority of diseases spread by their kind to humans.

 Stop Mosquitoes = Stop Heartworm

 So how do we do that?  Remove any and all standing water outside on your property.  By this I don’t mean go and fill in a pond or stream, just don’t leave a pail lying outside that can hold water because mosquitoes will breed in it.

Dog Heartworm Symptoms

Generally speaking, the symptoms of dog heartworm in a dog is lethargic and sluggish behavior.  The heartworm symptoms also include shortness of breath and extra sleeping. These symptoms are caused by the parasite congesting the heart.  This causes a lack of proper blood flow and an eventual heart attack followed by death. A nasty way to go, best get your dog tested.  For the $50-60 cost, it’s worth it.

Heartworm Testing 

Laboratory Testing
Laboratory Testing

If you have a dog and you live in an area where mosquitoes exist, then you should be having your dog regularly tested for heartworm.  The test should be performed by a veterinarian and should be done annually. The test is usually about $50 ($60 here in Canada). It only takes a few minutes as they just need to take a blood sample.  The results are typically back within 48 hours.

The test involves an investigation of the blood under microscopic conditions.  The test looks for eggs and/or larvae that are in the bloodstream. The dog heartworm reproduces inside the host and releases its eggs into the bloodstream. That’s how the test works. Next, we’ll take a look at dog heartworm treatment.

Dog Heartworm Treatment

There is a simple and effective treatment for heartworm but it is best in the early stages of the parasite.  Once the parasite has replicated and grown within the heart, there can be complications from sudden mass death.  The best thing to do if never having treated your dog for heartworm before is to have a veterinarian test your dog and direct the proper course of treatment.  

If you have already previously had your dog tested and the test was negative, then treatment and prevention are simple.  There is a product called Revolution, that you can treat your dog with and it also kills fleas. It’s easy to administer and does the job.  But make sure you’ve tested your dog at the vet first. That way you won’t be causing any potential complication scenarios to occur.

 Dog heartworm is both preventable and treatable.  If caught early, it is easily avoided with a simple treatment.  Although Mosquitoes are basically unavoidable, they too can be thwarted with a little ingenuity. Use Citronella based oils and products to deter the little bloodsuckers.  They do, after all, carry some pretty nasty things that can harm people too.

Six Frequently Asked Questions About Dog Heartworm

1. Can Dog Heartworm Infect Humans?

Technically, yes.  Although they don’t tend to be able to complete their cycle.  According to, dog heartworm in humans will usually wind up in the lungs and will appear as a round lesion in the lung.  Again though, you can only get this from a Mosquito. They are the carriers.

2. Can Cats Get Dog Heartworm?

A young cat.
A cat can get heartworm but they do have a natural resistance, so it’s unlikely compared to a dog’s chances.

Yes.  Although Cats have a natural resilience towards not getting infected, they technically can contract the parasite if an infected Mosquito bites them. 

3. Can Dogs Get Heartworm From Cats?

Not likely.  The dog heartworm is transmitted via Mosquitoes for one thing.  Cats are naturally resistant, somewhat, to heartworm to begin with.  They have a much less likely chance of getting heartworm from an infected Mosquito, although it is possible.  So the answer is no, a dog gets heartworm from Mosquitoes, not Cats. 

4. Can A Dog Get Heartworm From Eating Something?

Not typically, no.  The only way would be if a dog ingested blood infected with heartworm and then also had a cut where the infected blood could enter the dog’s bloodstream or flesh.  So, although technically possible, it is remote and extremely unlikely.  

5. Does Dog Heartworm Come Out In Poop?

No.  If you see something wriggling in your dog’s feces, it is likely something else infecting your dog.  There are other parasites that infect different areas than the heartworm which moves to the heart and does not typically infect the digestive system.  Take a sample of the dog’s poop in a plastic sealable bag to the vet so they can run tests to determine what type of parasite it is. This way they can determine the correct treatment. 

6. Can Reptiles Get Dog Heartworm?

A Bearded Dragon.
A Bearded Dragon Cannot Get Dog Heartworm.

No.  Reptiles cannot get dog heartworm, it is a parasite that targets mammals.  However, reptiles have a whole slew of parasites they can get on their own without needing heartworm affecting them on top of it.


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