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Heartworm Signs, Treatment and Prevention

Posted by Reedy Creek Vet on 17 April 2023
Heartworm Signs, Treatment and Prevention

This National Heartworm Awareness Month, the Reedy Creek Vet team would like to keep pet owners informed about the risk of heartworm for dogs and cats, and how to best protect pets from this dangerous disease.

What is heartworm disease?

Heartworm disease is caused by infestation with parasitic Dirofilaria immitis worms, which are commonly known as heartworm.

How do pets become infested with heartworm?

Immature D. immitis worms are transmitted between animals by mosquito bites. Whilst dogs are the normal hosts of heartworm, cats can also (less commonly) become “atypical” hosts for heartworm.

Once the immature D. immitis worms have been “injected” into a susceptible animal by a mosquito feeding on the animal’s blood, they migrate through the animal’s tissues, largely ending up in pulmonary arteries (the blood vessels leading from the heart to the lungs) where they grow and develop to adulthood.

What symptoms does heartworm infestation cause?

Dogs with early heartworm disease or low numbers of heartworms in their pulmonary arteries frequently show no obvious symptoms of unwellness.

However, when significant numbers of adult heartworms begin to accumulate, the dog suffers progressive damage to the blood vessels and tissues within their lungs. It is also common for infected pets to eventually develop heart disease, as well as potential damage to their liver and kidneys, which can prove fatal.

Dogs with significant heartworm infestation frequently develop:

  • Persistent coughing

  • Weight loss

  • Lethargy and reduced exercise capabilities

As the disease progresses, dogs may also develop:

  • Symptoms of heart failure, such as fluid within the chest or belly

  • Breathing difficulties

  • Weakness

  • Pale gums

  • Fever

  • Poor appetite

  • Vomiting

  • Jaundice (yellow discolouration of the skin, eyes and urine due to liver problems)

Cats infected with heartworm generally develop heartworm-associated respiratory disease, involving symptoms of coughing, wheezing, poor appetite, and vomiting.


Whilst heartworm can be treated, the treatment itself can be risky and prolonged, as killing the worms can result in dangerous (and potentially fatal) inflammation and shock within the pet’s body, and needs to be done gradually.


Fortunately, there are many effective options for heartworm prevention in dogs and cats, including monthly topical liquid products for cats, and long-acting injections or monthly chews or tablets for dogs.

We recommend year-round prevention for all at-risk pets.

For advice on the best heartworm prevention options for your pet, contact the Reedy Creek Vet team on (07) 5593 8395 or pop into the clinic for a chat. If you are worried that your pet may have been unprotected against heartworm, we’d recommend booking an appointment with one of our vets for further assessment.

Author:Reedy Creek Vet