Heartworms (Dirofilaria immitis) are becoming increasingly prevalent in Canada, making prevention more important than ever. While the disease remains less active during the winter months, the risk surges as temperatures rise. With the return of warm weather and the emergence of mosquitoes, your pets become vulnerable to infection. Taking proactive measures is essential to keeping them safe.
Heartworm disease is difficult and complicated to treat, so it makes good (and economical) sense to prevent it from occurring in the first place. It is caused by a parasite transmitted through a mosquito bite, which then lodges and multiplies in the main blood vessels of your pet’s heart.
The adult worm, known as Dirofilaria immitis, resembles white spaghetti and can grow up to 30 cm long. If left untreated, it can migrate to your pet’s pulmonary arteries, right heart, and vena cava, leading to severe and irreversible heart and lung damage. In some cases, heartworm infection can cause life-threatening symptoms and even death.
Heartworm prevention is primarily recommended from June to November when mosquitoes are active in Canada. Various preventive medications are available, so it's best to consult your veterinarian to determine which one is most suitable for your dog.
Symptoms to watch for include exercise intolerance, chronic coughing, stunted growth, fatigue, sudden loss of appetite, loss of balance, and shortness of breath. However, don’t wait for these signs to appear before taking action—prevention is always better than cure for this challenging and painful disease!
To determine whether your pet needs preventive treatment for heartworm, the easiest method is a blood test to check for the presence of microfilariae. These tests are performed between five and seven months after a potential infection—the time it takes for heartworms to develop into microfilariae. Therefore, testing is typically recommended around April.
If the test is negative (indicating the absence of microfilariae), the animal is placed on a preventive medication program. This way, if a mosquito bites your pet and transmits microfilariae, the treatment will prevent the larvae from developing and spreading. The heartworms won’t be able to mature—proving that you made the right choice in taking preventive measures!