What Is Heartworm In Dogs?

Those poor hearts 💕

heartworm in dogs

As a dog parent, you’ve probably heard the word “heartworm” so many times. But what exactly is heartworm in dogs?

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, who shared everything you need to know.

What exactly is heartworm in dogs?

“Heartworm is exactly what it sounds like — a worm that lives in the heart of dogs,” Dr. Marteney told The Dodo. “Technically it lives in the pulmonary artery (the large vessel that carries blood from the heart to the lungs).”

A heartworm will move with your dog’s blood flow, which causes physical damage.

“There is physical disruption of blood because there's something in there that shouldn't be in there,” Dr. Walther told The Dodo.

And since your dog’s body is trying to fight off the heartworm, that response can cause some problems, too.

“There's also inflammation, which is causing damage to all of the cells that this worm is touching,” Dr. Walther said.

And when the worm dies, it could also create blood clots.

How do dogs get heartworm?

Mosquitos are how dogs get heartworm in their arteries.

“This parasite is transmitted between dogs by mosquitoes,” Dr. Marteney said.

When a mosquito bites a heartworm-infected dog, it doesn’t just suck his blood — it also ingests microscopic heartworm larvae. Then, when that mosquito bites another dog, that dog becomes infected with heartworm.

“The larvae grow and develop in the mosquito, and when they’re more mature, they are deposited on the skin when the mosquito bites another dog,” Dr. Marteney said.

Heartworm symptoms in dogs

In a lot of cases, your dog might not show any heartworm symptoms at all — which is super scary, but also why testing is so important.

In some cases, you might see mild heartworm symptoms in dogs, like:

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

In other cases, you might notice more severe heartworm symptoms in dogs, including:

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

Heartworm can also lead to other issues you won’t even be able to see for yourself (but your veterinarian can identify), like:

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

Heartworm prevention for dogs

Heartworm in dogs is no joke, so it’s crucial to always keep your pup on preventative medication.

“Heartworm disease is easily preventable with prescription medications that are readily available from any veterinarian,” Dr. Marteney said. “All dogs should be on routine prevention year-round.”

According to Dr. Marteney, there’s injectable heartworm prevention for dogs that can either be given once every six months or once per year (depending on the exact version your dog receives).

You might also choose to give your dog an oral heartworm medication, which needs to be administered monthly.

Heartgard Plus is a highly rated chewable tablet designed to prevent heartworm in dogs. 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 aren’t just great for heartworm prevention in dogs — they’ll also protect your pup from fleas, ticks and intestinal parasites.

Simparica Trio is a combination medication that works to prevent 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 these, so it’s best to talk to your vet to find out which heartworm medication is the best preventative option for your dog.

Heartworm treatment for dogs

If your pup does end up with the disease, heartworm treatment for dogs is possible. It is, however, super intense.

“Heartworm treatment in dogs is a complex, difficult process,” Dr. Marteney said. “It’s expensive, difficult, exhausting and hard for the pet to go through — especially for a disease that is easily preventable with routine heartworm preventatives.”

But before the actual heartworm treatment can start, your vet needs to determine just how bad your dog’s case is.

“The first step in treatment is to stage the disease ... This staging can help guide treatment and indicate how well a dog will tolerate the treatment,” Dr. Marteney said.

That means your vet would have to run all sorts of tests on your dog — including X-rays, a blood work panel and a urinalysis — to figure out just how severe his heartworm is.

Knowing the seriousness of your pup’s disease will determine what his treatment will look like.

“Treatment starts with oral medications,” Dr. Marteney said.

Oral heartworm treatment for dogs kicks off with preventative medication to target the heartworms that haven’t matured yet and keep your dog from getting reinfected throughout treatment.

“An antibiotic (doxycycline) is also started to control Wolbachia, an organism that lives inside of heartworms and makes it easier for them to survive,” Dr. Marteney said.

Taking care of that organism means your dog’s heartworm treatment will be more effective.

On top of those medications, your vet will also administer a steroid and an antihistamine to manage the inflammation.

Your dog will be on all those meds for about a month, and then your vet will give him a melarsomine injection, which is the stuff that’s actually going to kill the heartworms.

“[It’s] an arsenic-based medication that effectively kills the adult heartworms,” Dr. Marteney said.

The melarsomine injection is a painful part of heartworm treatment, and your dog will have to stay in the hospital for the whole day afterward to make sure he doesn’t develop an anaphylactic reaction (aka a severe allergic reaction) or pulmonary embolism (aka a blockage of an artery in the lung).

After a month, your dog will need two more melarsomine shots — administered a day apart — which also means more hospitalization after each one.

Following heartworm treatment, the best way to care for your dog is to make sure he gets a lot of rest.

“Exercise restriction is imperative through the treatment and for an additional 60 days afterward (i.e., at least five months of strict rest during treatment),” Dr. Marteney said.

That’s because physical activity could cause heartworms to break loose and harm your pup. So, he should stick to slow, low-impact walks.

Since heartworm in dogs can be so harmful and the treatment is really intense, the best way to keep your pup happy and healthy is by making sure you stay on top of annual testing and his preventative medications.

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