Dog Tips

The Ultimate Guide to Heartworms in Dogs

Everything You Need to Know About Heartworms in Dogs 

Nobody likes to be bit by a mosquito, but for your dog, a mosquito bite is much more than a nuisance – and can be deadly. Heartworms pose a severe threat to dogs. Even though they are easily prevented, they are challenging to get rid of once contracted. Often hard to tell until it is too late, heartworm disease takes the lives of many dogs every year. It is essential to know what Heartworm disease is, how your dog could get it, and what happens if they do.

This sounds very daunting and disheartening as a dog owner, but don’t worry! There are excellent resources to protect your dog from heartworm disease. Let’s talk about what it is, what the symptoms are to look out for, and why prevention should be a top priority.

What is Heartworm Disease?

Heartworm disease is a condition that can cause severe lung disease, organ damage, and heart failure. If untreated, it is fatal. The name comes from the parasitic worms that live in an animal’s heart, lungs, and blood vessels. These worms are called Dirofilaria immitis, and once they find a host, they will live through their whole life cycle inside a dog’s organs. They will mature into adults and reproduce, proving difficult to remove. Adult female heartworms will release their larvae, microfilariae, into an infected dog’s bloodstream. These larvae will mature over the course of 6 to 7 months and have a lifespan of 5 to 7 years. The number of worms inside a dog can vary, but on average, the “worm burden” – the term used to describe all the worms inside an infected dog – is 15. This number can go up to 250 in severe cases. Watch out to make sure that your dog is not experiencing blood in their stool or that your puppy doesn’t have diarrhea.

How do dogs get Heartworms?

So now you know what it is but – how is it transmitted? Is it contagious among dogs? Since it is transmitted through mosquitos – no. Although your dog will not catch it from a fellow canine, they can get it from any small mosquito bite. Since infected dogs house the offspring of adult heartworms – microfilariae – when a mosquito bites a dog with heartworms, they get these young heartworms into their own system. After about 10-14 days, they become infective larvae. As this mosquito goes along biting other dogs, it spreads these eggs. This is when they enter the bloodstream through the bite wound and start the process of maturing into adult heartworms. As mentioned above, this will typically take 6-7 months.After the mosquito has transferred these larvae, they will make any dog their home to reproduce, spread, and eventually attack its major organs. These tiny transferrable larvae use the mosquito as a delivery method to find an unknowing host. Speaking of offspring, explore the best DNA tests for dogs.

As mentioned above, it is not transferrable from dog to dog. But, an infected dog can deposit larvae to a mosquito that will eventually go and bite another dog, and the cycle continues. If there is an infected dog in a community, there is definitely at least one mosquito around carrying the parasitic worms.

Areas That Heartworms Are Most Common

Although Heartworm disease has been found across the globe, it is more common in some geographical regions. According to the Alberta Veterinary Medical Association, the higher-risk areas in Canada include the southern regions of Ontario and Quebec, Manitoba, and the Okanagan in British Columbia. Ultimately, if you are somewhere with mosquitos – everywhere – your dog is at risk. There is no “safe zone” when it comes to heartworms. But it is good to know higher-risk areas to be extra careful.

Symptoms and How to Tell If Your Dog Has Heartworms

The tricky thing about noticing heartworms is that they are small and located inside your dog. It is impossible to know if your dog has been bitten by a mosquito when it comes in from your yard, and you won’t be able to see these worms migrating through your dog’s system. Puppy treats might make it easier to wipe paws and tails before they return to the house.Although some dogs won’t show any symptoms at all, others will give indications that something is amiss. The only way to confirm heartworms in a dog is via blood tests administered by your vet. While you wait in the office, stream some of the best puppy movies to pass the time.

If you notice any of these symptoms below, take your dog to the vet immediately. Further, frequent checks might be beneficial if your dog is not protected against heartworms.

The different symptoms dogs show represent varying classes of “worm burden” – or the number of worms they have in their system. Dogs with low worm burdens will show minimal symptoms, while severely infected dogs will get very sick.

Here are the four classes:

  1. No symptoms – Dogs who are initially infected or have a low worm count will often show no signs at all. If they start showing symptoms, they will be hard to notice.

  2. Mild to moderate symptoms – Dogs in this second class of worm burden will show minimal symptoms such as a cough or fatigue after exercise.

  3. More severe symptoms – Dogs at this stage will start to show obvious signs, and their organs are beginning to be severely affected. In class 3, your dog will likely need to undergo a chest x-ray to survey the worm burden and extent of infection.

  4. Most severe symptoms – Dogs in class 4 have a significant worm burden and will be very sick. This is also known as Caval Syndromeas the heartworms in the infected dog entirely block the blood flow to the heart. In class 4, life-saving surgery to unblock these vessels is the only measure.

In general, the symptoms to look out for are as follows. They will worsen in severity as a dog moves through the 4 classes of worm burden.

  • Mild Persistent Cough

  • Lethargy

  • Weight loss

  • Swollen stomach

  • Difficulty breathing

These are all signs that heartworms are starting to encroach on a dog’s organs and lungs. Get your dog checked out immediately if you see any combination of these symptoms – catching this disease early is vital, so no sign is too small!

Preventing and Treating Heartworms in Dogs

All of the information about heartworms can be stressful and disheartening. No dog owner wants their dog to go through this disease or deal with the removal process. Prevention is the best thing you can do. Different forms of prevention range from topical ointment, oral tablets to injections. All of these medications can be lifesaving and must be kept up with – depending on the type of medication. Consult your vet about what method is best for you and your dog. To soothe your pup’s tummy, serve them some rice.

There are medications to treat heartworms, but they are often costly. They can also have very uncomfortable side effects for your dog. But, if a dog is infected with Heartworm disease, it is often the only way. Melarsomine dihydrochloride (Immiticide and Diroban) and Advantage Multi for Dogs are approved and widely-used treatments. One is administered through injection to attack adult heartworms, and one is used topically to kill the offspring of adult worms. This treatment requires consistent upkeep and vet visits.

Getting your dog tested for Heartworm disease is another great way to mitigate infection. Ultimately, seeking preventative care is your best option. Stay educated and aware of the possible symptoms. Always consult your vet if you want to get your dog tested, treated, or protected against heartworms. You can also discover pet first aid tips.

  1. “Heartworm in Dogs,” Alberta Veterinary Medical Association,, n.d.

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