How Do Dogs Get Heartworms? Causes, Symptoms, And Ways to Prevent Heartworms in Dogs

How Do Dogs Get Heartworms? Causes, Symptoms, And Ways to Prevent Heartworms in Dogs

As a dog owner, you must be constantly worrying about your dog’s health. Be it a minor disease or even a life-threatening one, you always try to keep your fur bud as safe as possible. If so, you probably have heard about heartworms in dogs. If not, don’t worry we’ve got you covered. As ugly as heartworms may sound, their impact is far worse than their name. Heartworms clog your dog’s heart, liver, and other vital organs which ultimately lead to death. Now the question that arises is how do dogs get heartworms?

So, How Do Dogs Get Heartworms?

The answer is Mosquito Bite! A mosquito bite can be very alarming for humans. Once we are bitten, we are prone to Malaria, Dengue fever, Zika fever, Elephantiasis (Lymphatic filariasis), and Japanese Encephalitis to name some. Similarly, mosquito bites can be dangerous for dogs too. Mosquitoes carry a parasitic worm called Dirofilaria immitis or heartworms that stretch from 12 to 14 inches and clog your little pooch’s hearts, lungs, and blood vessels. What we’re telling you is not a fictitious horror story; it’s a very real heartworm infection that killed millions of dogs. So, if you’re interested, make sure to read further!

How Do Dogs Get Heartworms from Mosquito Bites?

Heartworms shelter inside the mosquito for a short period of time for making their infective nature more effective. So, the mosquitoes are just the intermediate host. After the mosquito bites your dog, heartworms continue to live and depend on the vital organs of your dog’s body. This makes our furry friends the definitive and ultimate hosts for heartworms.

The Heartworm Life Cycle

Once a dog gets bitten by the mosquito, the heartworms start doing their work. The adult females start releasing their offspring that are known as microfilariae into your dog’s bloodstream. Again, if another mosquito bites a newly infected canine then the microfilariae that resided inside the canines will migrate to the mosquito.

After around 10 to 14 days, the mosquito becomes the host for the heartworms and when it bites another dog, those larvae enter the dog’s body. This process continues and takes around seven months for the infective larvae to grow into adults. Once matured, heartworms start mating and produce even more microfilariae to complete the lifecycle.

Here’s an illustrated guide to the heartworm lifecycle from FDA.

The Four Classes of Infestation

One thing you must know is that this disease is not contagious which means your dog can’t be infected just by hanging around with dogs suffering from heartworms. As long as the dogs aren’t bitten by the infected mosquito, they won’t get infected.

The impact of heartworms on your dog directly depends upon how many heartworms have been living inside them. There’s a term for that and that’s known as worm burden.

The severity of the condition can be classed into four:

Class 1: Absence of Symptoms

Within this class, dogs either show no signs of heartworm infestation or mild symptoms that are not detectable.

Class 2: Mild/Moderate Symptoms

Dogs in this class show some doubtful symptoms that are not severe. These include mild cough and fatigue after moderate activity.

Class 3: Slight Severe Symptoms

In class 3rd, dogs generally require their chest x-rayed to determine the extent of internal damage. Those dogs show clear signs of discomfort and pain. Over that, they’ll also have a sudden change in their appearance.

Class 4: Alarming Symptoms

This class is also known as Caval Syndrome. Dogs in this class have a massive worm burden that physically blocks the flow of blood from the heart. This life-threatening situation requires a very risky surgery to quickly remove the heartworms from the dog’s body.

You might also be interested in How Can Dogs Get Worms?

Symptoms Of Heartworm Disease in Dogs

It can be difficult to determine whether a dog has adult heartworms by observation but the severity of heartworm disease is related to how many worms are living inside the dog’s worm burden, how long the dog has been infected, and how the dog’s body is responding to the presence of the heartworms. Here are some symptoms that you may observe if your dog has heartworms:

  • If your pup is coughing and they don’t have any food or dust allergies then it’s a red flag. This suggests that the pup might be undergoing Class 1 infestation. Coughing becomes more severe once worms overcrowd their lungs.
  • Fatigue from a moderate activity suggests that your dog could be dealing with Class 2 infestation.
  • Nosebleeds and unusual bruising can be observed too. Infected dogs can also experience difficulty in breathing.
  • Compare your pup with their previous appearance, they might look slick and undernutrition once they are infected by the bloodworms.
  • Another sign of heartworms may be abnormal lung sounds, although they are also associated with other upper respiratory conditions.
  • If you notice bloody dark urine, consider it a serious condition and call your vet as soon as possible.
  • You might also notice that your dog’s chest protrudes or has a bulging appearance. While the worms themselves can create the problem, it’s exacerbated by extreme weight loss.

Ways To Prevent Heartworms in Dogs

While Heartworms can be a life-threatening condition, there still are few ways to effectively prevent heartworms in dogs. They are:

1- Provide them best dog food

Although home-cooked foods are best for dogs, you cannot manage to cook them a meal every time, right? If you can’t manage to cook it yourself, look up dog food that has whole food ingredients, carbohydrates, and proteins. By doing this, you’re boosting your dog’s immunity power and thus preventing heartworms.

2- Regular Appointments

Make sure you follow up with regular vet appointments at least once in two months. Your vet is fully qualified to detect and treat the illness in your dog accordingly. So, you can completely trust them to pick signs and symptoms that you might have missed.

3- Use anti-heartworm medicines

Consult with your vet and then you can choose the monthly topical drug in a tube that can be squeezed on your pet’s back. The injectable product which lasts 6 months at a time could also be chosen. Or you could select the oral tablet to be taken every month.


Overall, Heartworms are deadly parasites that are no less scary than horror movies. These worms cause life and death situations for your dog so we recommend you to follow the guidelines we’ve mentioned before and make your pooch safe and sound.

Thank you for reading the article.

To explore more, check out other articles that we have covered on dogs and worms. 

Has your dog ever been infested by heartworms? What symptoms did you notice at first? And How did you treat them? We would love to hear from you. Please share with our community by leaving a comment below!

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