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How Does a Dog Get Heartworms?

Protecting your pup’s health is a top priority as a dog owner. It includes protecting them from the dangers of heartworms. But you may be wondering how your pooch can get heartworms. It is essential to learn more about the condition to better protect your furry friend. 

In a nutshell, warm conditions increase the risk of heartworms. It is because they are typically transmitted by mosquitoes. 


Mosquitoes Transmit Heartworms


Mosquito bites typically spread heartworms or Dirofilaria immitis. According to experts, your pup is a definitive host because heartworms can thrive and reproduce in them. When a mosquito with the infection bites your pooch, the larvae will develop into fully grown heartworms. 

It takes anywhere from six to seven months. They will live in your pup, where they will reproduce. Their offspring (microfilariae) live in your pup’s blood vessels.


Transmission of Heartworms


A mosquito may pick up this offspring when it bites your furry friend, spreading it to other dogs. They can live in your dog’s heart for approximately seven years. Your infected dog may be hosting about 15 heartworms on average. 

However, your pup may host only one worm or up to 250 worms in other instances. So, you should seek immediate vet attention if you suspect your canine friend has heartworms.


Symptoms of Heartworm Disease


According to the FDA, there are four stages to this condition:

  • Class 1 – During this stage, there are typically no noticeable symptoms. If there are, they could be in the form of a light cough.

  • Class 2 – Symptoms will begin appearing at this stage. Your pup can experience an occasional cough or seem unusually fatigued after an activity.

  • Class 3 – Symptoms at this stage are more noticeable. Your dog may tire easily after light activity. They may also have a persistent cough or difficulty breathing in some cases.

  • Class 4 – This is also referred to as caval syndrome. It happens when there are too many heartworms that blood cannot flow unhindered back to your pup’s heart due to the blockage. When this happens, it often requires emergency surgery. If left untreated, it is potentially fatal. Fortunately, not all pups with heartworms get to this stage. 


Protecting Your Dog From Heartworms


While mosquitoes may increase during the warm season, protecting your pooch throughout all seasons is advisable. Few over-the-counter products that protect against ticks and fleas can also keep mosquitoes at bay. Your pet doctor may recommend an oral pill to be taken once a month or a topical agent. You should ensure your pet does not skip a dose to keep them healthy and safe.




The warm season is perfect for you and your furry companion to spend time outdoors. However, it also increases the chance of your dog catching heartworms. Fortunately, taking a few preventative steps will protect your dog from mosquitoes and heartworms.

For more on how to care for your dogs, visit Eastern Animal Hospital at our office in Baltimore, Maryland. Call (410) 633-8808 to book an appointment today.

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