Heartworm Season

Every summer in Ontario, our canine friends are at risk of infection with heartworm, also known as Dirofilaria Immitis. In fact there are hundreds of cases in Ontariomosquito.jpg every year, and the prevalence has increased significantly in the last several years.

Heartworm disease is caused by a parasite that is passed from an infected animal to an uninfected animal through mosquitoes carrying the larval form of the parasite. Therefore, whenever mosquitoes are active, dogs are at risk of contracting this devastating disease.

Once a dog is infected with heartworm, the larva survives within the dog’s blood heartworm_heart.jpgvessels, where it undergoes a maturation process. The adult heartworm, typically 6 to 18 inches long, will eventually take habitat in the large chambers and vessels of the heart. This process takes 6-7 months to occur.

The signs of heartworm infection initially include coughing and exercise intolerance, and can eventually lead to more serious conditions like congestive heart failure, anemia, weakness and collapse, and eventually death.

There are treatments for animals infected with heartworm disease. However, both medical and surgical options as treatment are very costly and can cause serious health problems as the adult worms die and break up within the blood stream. A much safer way is to prevent your pet from contracting heartworm.

Heartworm can be prevented by using a once monthly medication during the period of time your pet is at risk of contracting the disease, typically June 1 – November 1. Not only do the heartworm preventative medications protect your pet from heartworm disease, they also provide protection against fleas, ticks, and gastrointestinal parasites.

It is important to know that giving certain heartworm preventatives to a dog already infected with heartworm is dangerous. Therefore, before starting the medication, it is important to have your pet tested for heartworm with a simple blood test. Even if you have used preventative medication in the past, testing is still important as no medication can be considered perfect and poor compliance with medication administration can lead to gaps in protection.

We recommend all dog owners have their dog tested for heartworm disease in the spring, before heartworm transmission season begins. It is a great time to also have a fecal sample from your pet analyzed for gastrointestinal parasites, and to have an annual blood work screen performed.

While heartworm is thought to be mostly a disease of dogs, it can also infect cats. While the disease is rare in cats, it typically causes more severe symptoms in infected cats than dogs. There are heartworm preventatives available for cats as well, and their use should be strongly considered by cat owners, especially if their cat spends time outdoors.

For more information on heartworm disease, see the Companion Animal Parasite Control website, the Ontario Veterinary Medical Association website, and the American Animal Hospital Association website.

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