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Heartworm: Why prevention is always the best treatment

With spring comes heartworm season, meaning it's important to get your dog tested and on preventative medication as soon as possible. Discover what prevention looks like and what kind of heartworm treatment is available for your pet.

Heartworm is transmitted by infected mosquitoes, meaning your pet could be at risk if they go outdoors—even if they’re not an outdoor pet. As heartworm can be fatal and there are few, if any, symptoms in the early stages of the disease, it’s important to protect your pet with preventative care and ensure they’re seen regularly by a vet.

If heartworm is left untreated, it can cause serious damage and illness, impacting the rest of your pet’s life. While there is treatment available for dogs, it’s expensive, time consuming, and hard on your pup’s health. Preventative treatment is more cost-effective and better for your pet’s wellbeing, making it a smarter choice for pet parents.

As there’s no heartworm treatment available for cats, and treatment can be expensive for dogs, we recommend annual testing in the early spring and monthly preventative medication to keep your pet safe.

Table of contents

  1. What is heartworm?
  2. How do pets get heartworm?
  3. What are heartworm symptoms?
  4. How is heartworm diagnosed?
  5. Is there a heartworm treatment?
  6. How can I prevent heartworm?
  7. FAQs

What is Heartworm? 

Heartworm is a serious and potentially fatal infection for pets. Transmitted by baby worms carried by mosquitoes, heartworm could be harmful to any pet that ventures outdoors. 

1. Heartworm in dogs

Dogs are natural hosts for heartworms, which means heartworms that live inside dogs mature, mate, and produce offspring. If heartworm goes untreated, their numbers can increase and cause lasting damage to the heart, lungs and arteries of your dog. Heartworm can affect a dog’s health and quality of life long after the parasites are gone.

2. Heartworm in cats

In cats, most heartworms don’t survive to the adult stage, so they have fewer fully-grown worms in their system. This means heartworm disease often goes undiagnosed in cats, but it doesn’t mean that it’s not serious—even if cats only have one worm, which is common, it can still be deadly. These immature worms cause damage in the form of a condition known as heartworm associated respiratory disease (HARD). 

How do pets get heartworm?

Pets can get heartworm through mosquito bites. After an infected mosquito bites an animal, the larvae take about six to seven months to develop into adult heartworms. The adult worms live and reproduce in animals’ hearts and blood vessels, and cause serious damage.

“Pets are at risk of heartworm in warmer months when mosquitoes are out. To keep your pet safe, we recommend testing in the early spring and ensuring your pet is taking monthly preventative medication during spring and summer.” — Dr. Cassandra Vlahaki | Head Veterinarian, Juno Veterinary

What are heartworm symptoms?

There are few, if any symptoms in the early stages of heartworm disease. This makes testing and prevention extra important. 

Common signs of heartworm

Common signs of heartworm change as the disease progresses. There are four classes, or stages, of heartworm disease. The higher the class, the worse the disease and the more obvious the symptoms:

  • Class 1: No symptoms, or mild symptoms like an occasional cough.
  • Class 2: Mild to moderate symptoms, like an occasional cough, decreased appetite and weight loss, and tiredness after moderate activity.
  • Class 3: More severe symptoms, like a sickly appearance, a persistent cough, tiredness after mild activity, and a swollen belly. Trouble breathing and signs of heart failure are common for classes 2 and 3 heartworm disease.
  • Class 4: Also called caval syndrome. There are so many worms in the heart that blood is physically blocked. Caval syndrome is life-threatening and can only be treated by surgery to remove the worms. 

How is heartworm diagnosed? 

Heartworm is diagnosed by a simple blood test. If your pet is diagnosed with heartworm, we may recommend more diagnostic tests to make sure they’re healthy enough to undergo treatment.

1. When should my pet be tested for heartworm?

We recommend testing if your pet is showing signs of heartworm, otherwise, we test in the early spring. 

2. Why do you test for heartworm in the early spring?

It takes approximately seven months to be able to detect heartworm in pets after they’re first infected, so we test in the early spring for three reasons:

  1. We want to make sure your pet didn’t become infected with heartworm in the previous season.
  2. If your pet is infected, we can treat the infection before it becomes advanced.
  3. We want to rule out infection before starting preventative medication. We recommend starting preventative medicine in the spring and summer when the mosquitoes are out, but preventatives can cause a dangerous reaction if your pet is already infected with heartworm.

3. When is heartworm season in Canada?  

Heartworm season starts in June and usually lasts until November. Current data suggests that for heartworms to become a threat, the temperature must be at least 14 degrees Celsius for at least four consecutive days. That’s why, in Ontario, we recommend preventative treatment from June through November. If your pet spends time in warmer climates over the winter, you should be giving your pet year-round protection.

Is there a heartworm treatment? 

There’s a heartworm treatment available for dogs, but there’s no treatment available for cats.

Treatment for heartworm for dogs involves a series of injections and strong medications. It’s expensive, time consuming, and potentially harmful for dogs. Treatment can cause serious complications like toxicity and life-threatening blood clots in their lungs, and your dog will need to be cage rested for six months while receiving treatment. However, it’s preferred to having your pet suffer with heartworm symptoms, which could be fatal.

“When it comes to heartworm, prevention is always safer than treatment.” — Dr. Cassandra Vlahaki | Head Veterinarian, Juno Veterinary

How much does heartworm treatment cost?

The average cost for heartworm treatment is in the thousands. Not only do you need to pay for multiple rounds of medication, treatment requires testing, x-rays, and in serious cases, surgery. Heartworm prevention is a more cost-effective option, with treatment starting as low as a few hundred dollars.

Basic testing and prevention starts at $320 pre-tax for six months of prevention medication, and includes heartworm and Lyme disease testing, and monthly preventative medication for heartworm, fleas, and ticks. You can also opt for a more comprehensive package, starting at $505 pre-tax. This includes basic testing and prevention, plus an annual wellness screen and fecal testing. The additional blood work helps with early detection and treatment for a variety of illnesses. Fecal testing can tell you if your pet is suffering from parasites like worms or giardia.

How can I prevent heartworm? 

The best way to prevent heartworm is with annual testing and monthly preventative medicine for your pet. Preventative medicine comes in chew form, or as a topical lotion that’s applied between your pet’s shoulder blades. 

Did you know? Monthly heartworm preventatives often include protection against other worms and parasites like roundworm, hookworm, fleas, ticks, and ear mites.

At Juno Veterinary, we offer a range of testing and prevention packages. Testing ensures we’re not giving an infected pet preventative medications, which can be dangerous. It also helps us treat heartworm in the early stages if your pet is infected.

1. Does monthly preventative heartworm medicine kill heartworm? 

No, monthly preventative heartworm medicine does not kill adult heartworm. Treating adult heartworm requires a separate and specific medication

It’s important to get your pet tested before starting any preventative medication. If your pet is infected with heartworm, preventatives can cause a serious and dangerous reaction. 

2. Can my pet still get heartworm if they’re taking monthly preventative heartworm medicine?

Yes, your pet can still get heartworm if they’re taking monthly preventative medicine. Preventatives are highly effective but they’re not foolproof. To make sure your pet’s monthly medication is most effective:

  • It needs to be taken on the same date, every 30 days
  • Your pet needs to take the whole dose
  • Your pets needs the right dose for their weight

Talk with your Juno Vet care team about the best preventative heartworm medicine for your pet.

Get unlimited 24/7 pet care at your fingertips With the Juno app, it’s like having a personal vet care team in your pocket. Get unlimited 24/7 support, easily schedule appointments, refill prescriptions, and explore your pet’s medical records and invoices.

3. Does my pet need heartworm protection year round?

If you live in a climate where the temperature is consistently below 14 degrees Celsius for a portion of the year, we recommend heartworm protection for the warmer months when mosquitoes are active. If you live in a warmer climate or you visit warmer clients during the winter, we recommend year-round protection.

Because heartworm is serious and hard to detect in the early stages, prevention is the best treatment. Book your pet for heartworm testing today and be sure to get the go ahead from your vet before starting any preventative medicine. Preventative medicines are effective, but they’re not 100%, so they’re best combined with routine testing. Schedule a visit with your Juno Vet before heartworm season—it could save your pet’s life.

Q. Is it really that important to give my pet their preventative medicine on the same date every month?

A: Yes, preventative medicine is very important to give preventative heartworm medicine on the same date every month. All monthly heartworm preventive products work by affecting the larval stages that have been picked up from a mosquito bite in the past 30 days. Preventatives don’t affect the juvenile and adult life stages of the heartworm, so it's critical to dose your pet every 30 days. Giving your pet their heartworm preventive on the same date each month will affect the larval stages acquired since the last dose. If you miss a dose, give your pet the dose as soon as possible and restart your 30-day countdown for the new date. Let your Juno care team know in the Juno app.

Q. If I give my pet a preventative, why do I need to test them every year?

A: No heartworm preventive is 100% effective in preventing heartworm disease. With annual testing we can detect the disease in its early stages and we can make sure it’s safe to continue giving your pet their preventative medicine. Annual testing should be part of every pet’s preventative wellness check-up.

Q. I have a puppy or a kitten. When should I start heartworm prevention?

A: Puppies and kittens are not born with protection against heartworm, so they’re at risk for becoming infected with heartworms from the first day of life. Heartworm prevention can be started as early as eight weeks, but it’s important to talk to your vet about what’s right for your pet.