What is heartworm, and how is it spread?

Heartworm in dogs is a common parasite that is spread through the bites of infected mosquitoes, which carry the larvae. The only way for heartworm to infect your dog is via a mosquito bite. If you have one dog with heartworm and one without, this means you don’t have to worry as it can’t be passed directly from dog to dog.

The heartworm larvae float around in the blood and tissue of the dog until they eventually settle in the heart and pulmonary arteries. They then develop into adult heartworm (Dirofilaria immitis). The adult worms cause problems for the respiratory system, and cardiac difficulties can result, including complete cardiac failure.

The Heartworm Life Cycle


Symptoms of Heartworm infections may include laboured breathing, exercise intolerance, dry and persistent cough and weight loss. Heartworm can also affect cats, although it is not as common. Similar symptoms can be seen in both cats and dogs. There are tests available from your veterinarian to test for heartworm prior to beginning preventative measures. Work with your veterinarian on a treatment plan if your dog does happen to return a positive result for heartworm.

You can help prevent heartworm with regular tablets or an annual injection. Prevention is essential to keep your dog protected from contracting heartworms. The injection can be safely given at the time of your pet’s vaccination and removes the need to remember to give your dog a monthly heartworm oral tablet or chew, but is ultimately your choice!

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