How Do Dogs Get Heartworm? Signs, Treatment & Prevention

Blue & White Veterinary Clinic • June 27, 2022
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If you’re a dog owner, you’ve likely heard about heartworm. What is it, how do you detect it in your dog, and how can it be treated and prevented?


Read on for some helpful information.

What is heartworm?

Heartworm is a parasite living in your dog’s heart and in nearby blood vessels which feeds on its blood. If you think it sounds serious, you’d be right. By the time your dog develops symptoms of heartworm, it’s often at an advanced stage of the disease.

How do dogs get heartworm?

Mosquito bites are the only cause of heartworm. If a dog has heartworm and is bitten by a mosquito, that mosquito becomes a carrier for the disease and will transfer it to other animals. Once your dog is bitten, heartworm larvae spread through its blood until they reach the heart.

What symptoms should I look out for?

It takes several months for larvae to mature, so symptoms may not show until there are a large number of worms in your dog’s heart and lungs. Symptoms can include:


  • Persistent dry cough
  • Shortness of breath
  • Weakness and lethargy
  • Low stamina
  • Avoiding physical activity
  • Decreased body conditioning


Exercise can exacerbate many symptoms of heartburn. If you notice any of these symptoms, you should immediately bring your dog to the vet for diagnosis and treatment.

I think my dog has heartworm - what do I do?

If you suspect heartworm in your dog, a proper diagnosis through urine and blood tests and x-rays is essential. Once your dog is diagnosed, it will go through three phases of treatment.


  1. Pre-treatment: This stage might not be needed for every case. It involves medicating at home for two to three weeks to try and reduce blood clot formation and roughening of the blood cell lining.
  2. Adulticide treatment: Your vet will administer a drug to kill the adult heartworm. It is most commonly delivered as two injections 24 hours apart. It can also be given as split injections, with an initial injection followed by the two adulticide treatments a month later. We recommend a check-up one week after your dog receives adulticide treatment.
  3. Microfilarial treatment: Your dog will have a short stay at the hospital to kill any baby heartworm.


A blood test is performed three weeks after the adulticide is administered. If the test is negative, heartworm treatment is finished and you can commence heartworm prevention.

How to prevent heartworm

Heartworm is a serious and potentially fatal condition that can be difficult to treat, so prevention is key. If your dog has heartworm, a preventative treatment can be dangerous and even fatal, so it’s crucial you have your dog checked by one of our vets first if you’re unsure.

When your puppy reaches 6-8 weeks of age, they can begin heartworm prevention. You can administer monthly tablets or top-spot applications at home, but the most convenient and effective treatment is an annual injection from your local vet, which your dog can receive once it’s 12 weeks old. If your dog hasn’t had heartworm medication for over six months, a blood test is needed to rule out potential infection before prevention can recommence.

Put your best friend in the best hands with Blue and White Veterinary Clinic

At Blue and White Veterinary Clinic, we’re committed to providing holistic dog care in a friendly environment. Our registered veterinarians treat all animals at our clinics and animal hospitals throughout the Mid North Coast, so you’ll be confident your pet will receive the best care.


Contact us today to speak to our team or book an appointment for your pet.

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