How Do Dogs Get Heartworm Disease?

And what do mosquitos have to do with it? 🦟

dog heartworm

Heartworm in dogs is super scary, so you probably want to do everything you can to make sure your BFF doesn’t get it.

But how do dogs get heartworm disease in the first place?

The Dodo spoke with Dr. Zach Marteney, a veterinarian and medical director at Meadowlands Veterinary Hospital in New Jersey, and Dr. Claire Walther, the parasiticides medical affairs lead at Zoetis Petcare, to find out what causes heartworm in dogs and how you can keep your pup safe.

What is heartworm in dogs, anyway?

Heartworm in dogs is just what it sounds like. The disease involves worms that live inside your pup’s heart.

Specifically, the worms live inside your dog’s pulmonary artery, which carries blood from his heart to his lungs.

“They spend their entire adult lives here, breeding and releasing microscopic worm larvae into the bloodstream,” Dr. Marteney told The Dodo.

Heartworms can cause a lot of damage to your dog by physically disrupting his blood, since there’s something in his artery that shouldn’t be there.

They can also cause inflammation in your dog’s body as his immune system tries to fight them off, as well as blood clots when the heartworms die after treatment.

How do dogs get heartworm, and what causes it?

Dogs get heartworm through mosquitos.

If a mosquito bites an infected pup, it ingests the dog’s blood as well as some microscopic heartworm larvae.

“When they first are transmitted by mosquitoes, they are millimeters in length,” Dr Walther told The Dodo.

The larvae then grow inside the mosquito.

Once they’re more developed and mature, the mosquito will actually release the larvae on another dog’s skin through a bite, and that dog will become infected with heartworm disease.

“They migrate through the mosquito’s bite into the subcutaneous tissues, then follow a complicated migration pattern through the dog’s body while continuing to mature,” Dr. Marteney said.

That’s when the parasites make their way through the dog’s system, until they ultimately get to the pulmonary artery.

“Eventually they arrive in the pulmonary artery, where they grow into adults and start sexually reproducing to continue the cycle,” Dr. Marteney said.

Luckily, an infected dog can’t directly give your dog heartworms.

“Heartworm-positive dogs playing in a dog park with a non-heartworm-positive dog — they're not going to transmit it dog-to-dog,” Dr. Walther said.

Heartworm symptoms in dogs

Keeping an eye out for heartworm symptoms in dogs is really important, but also super tough since a lot of dogs won’t show any symptoms at all.

But in some cases, your pup might show mild heartworm symptoms, like:

  • Coughing
  • Decreased energy level
  • Running out of breath quickly while exercising

More severe symptoms include:

  • Significant coughing
  • Coughing up blood
  • Significantly increased respiratory rate
  • Difficulty breathing
  • Decreased overall energy level
  • Abdominal swelling

Plus, heartworm can cause other issues you won’t be able to see (but your vet should be able to spot), like:

  • Internal inflammation
  • Increased blood pressure
  • Heart failure
  • Liver damage
  • Kidney damage
  • Blood clots

Heartworm prevention for dogs

Since mosquitos are pretty impossible to avoid, preventative heartworm medication is super important for dogs.

There are injectable options as well as monthly oral medications.

Heartgard Plus is a chewable tablet designed to prevent heartworm in dogs, and it has some of the best ratings. It’s available for dogs up to 25 pounds, dogs 26 to 50 pounds and dogs 51 to 100 pounds.

There are also oral combination medications that will protect your pup from fleas, ticks and intestinal parasites in addition to preventing heartworm.

Simparica Trio is a combination medication that targets heartworm, fleas and ticks. It’s available for dogs 2.8 to 5.5 pounds, dogs 5.6 to 11 pounds, dogs 11.1 to 22 pounds, dogs 22.1 to 44 pounds, dogs 44.1 to 88 pounds and dogs 88.1 to 132 pounds.

You need to have a prescription for heartworm prevention, so it’s best to talk to your vet to find out which preventative option is best for your dog.

Treating heartworm disease can be a difficult and painful process for your dog, so it’s important that he’s protected against the parasite. Staying on top of preventative meds — and your pup’s vet visits — is the most effective way to keep your dog from getting heartworm disease in the first place.

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