What You Need To Know About Heartworm Treatment For Dogs

Here's why it's so tricky.

heartworm treatment for dogs

You hope your dog will never get diagnosed with heartworm disease. But if he does, it’s important that you work with your vet to come up with a treatment plan ASAP so he can get healthy again.

The heartworm treatment process is involved, painful and takes a really long time. But if you stick super carefully to the protocol, and start it early, your pup should be on his way to being heartworm-free.

The Dodo spoke with Dr. Zach Marteney, a veterinarian and medical director at Meadowlands Veterinary Hospital in New Jersey, who explained what heartworm treatment is like for dogs and what you can expect every step of the way.

What is heartworm in dogs?

Heartworms are worms that live inside of an animal’s heart that can cause physical damage and inflammation, as well as lead to serious and scary things like liver damage, kidney damage, blood clots and even heart failure.

(That’s why it’s so important to treat heartworm disease if your dog contracts it.)

“They absorb oxygen and other nutrients from the blood,” Dr. Martney told The Dodo, which can be pretty damaging to your pup’s health.

Dogs get heartworm disease through mosquito bites: After a mosquito bites an infected dog, it ingests heartworm larvae that will mature inside the mosquito until the mosquito bites an uninfected pup. The larvae then get transferred to the new dog and make their way to his pulmonary artery (aka the artery that brings blood from the heart to the lungs), where they fully mature and reproduce.

How heartworm treatment for dogs works

Heartworm treatment for dogs is a long and involved process, but it’s crucial if your pup tests positive for heartworms.

“It’s important to stick to this protocol as closely as possible,” Dr. Marteney said. That’s because each step is vital for clearing up your dog’s disease and getting those invasive worms out of his system.

According to Dr. Marteney, it’s extremely important to make sure your dog’s activity is super restricted throughout treatment to prevent health complications.

Staging heartworm disease

The first part of your dog’s heartworm treatment involves staging the disease, which is when your vet runs a series of tests to determine how severe his case is.

“This includes a full blood work panel to check internal organ function and blood cell counts, as well as chest X-rays to look for evidence of damage to the heart and lungs, and urinalysis to look for protein in the urine,” Dr. Marteney said. “Sometimes an echocardiogram [aka an ultrasound of the heart] is necessary to help identify the severity of the disease.”

Dog heartworm prevention medicine

Once you’ve figured out the seriousness of your dog’s heartworm, the next step is to give him some prevention medicine to target the younger worms in his system.

“A monthly heartworm preventative is started to control the microfilaria (the immature stages of the heartworms that are being born) and prevent reinfection during treatment,” Dr. Marteney said. “This is continued long-term for the rest of the pet’s life.”

Your vet will also put your dog on an antibiotic to deal with Wolbachia, which is a bacteria that lives inside heartworms and helps keep them alive.

“Killing the Wolbachia helps make the eventual treatment for the actual heartworms more effective,” Dr. Marteney said.

Manage inflammation

After prevention medicine, the vet will give your pup medications to manage the inflammation caused by his heartworm disease.

“A steroid (prednisone) and an antihistamine (diphenhydramine, or Benadryl) are used to decrease the inflammatory immune response in the lungs and minimize the risk of an anaphylactic reaction to the dying organisms,” Dr. Marteney said.

This phase lasts two months: a one-month period when your dog will be on the anti-inflammatory medications, and then a one-month period when he’s off them.

“These medications are continued for about a month, then about a month after they are finished, the actual heartworm treatment begins,” Dr. Marteney said.

Heartworm killer medication

“Adult heartworms are killed with a medication called melarsomine,” Dr. Marteney said.

Melarsomine is an arsenic-based injection and can be pretty painful for your pup, so your vet will also prescribe pain medication.

Although melarsomine can cause your dog a lot of discomfort, it’s unfortunately a crucial step in your dog’s heartworm treatment.

Melarsomine also comes with some pretty serious risks, which is why your dog will need to be hospitalized after he gets his shot.

“There is a risk of an anaphylactic reaction, and as the worms die, they may come loose and cause a blockage in the vessels of the lungs (a pulmonary embolism),” Dr. Marteney said. “These are life-threatening, so it’s very important that the pet is monitored at the hospital for the entire day after receiving the medication.”

After that, your dog will get another round of anti-inflammatory meds to reduce that risk further.

“Another course of prednisone and diphenhydramine helps minimize the risk of anaphylactic reactions as the worms continue to die in the days after the medication,” Dr. Marteney said.

One month later, your pup will get two more melarsomine injections a day apart from each other, and he’ll be hospitalized after each one. He’ll also be prescribed another round of steroids and antihistamines.

Continue dog heartworm prevention medicine

After that, you’ll just use your dog’s monthly prevention medicine to keep new heartworms at bay, and then take him to the vet for another heartworm test several months later to find out if the disease cleared up.

“Monthly preventatives should be continued to prevent reinfection,” Dr. Marteney said. “A recheck heartworm test should be done nine months after treatment is completed (i.e., one year after the initial positive test).”

The results will determine whether your dog needs another dose of melarsomine or if he’s officially cleared of heartworms and just needs to continue with his prevention medication.

“If the test is negative, then the treatment was successful and no further treatment is necessary, other than monthly preventatives,” Dr. Marteney said. “If the recheck test is positive, another two-dose protocol [of melarsomine] should be administered … with hospitalization and another course of prednisone and diphenhydramine, and continued exercise restriction for an additional two months.”

Slow-kill heartworm treatment

There’s also a slow-kill heartworm treatment, which is essentially just giving your dog monthly heartworm preventatives until the worms eventually die.

But while a slow-kill heartworm treatment avoids all the painful injections, steroids and hospital visits, it takes a really long time and isn’t recommended.

“This can take three to five years, and is not approved by the American Heartworm Association,” Dr. Marteney said.

Since heartworm treatment is such a long, involved, painful and expensive process, the best thing you can do for your pup is to get him on prevention medication and keep him from getting it in the first place.

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