Dog Heartworm Test

Heartworm is a very serious parasite that resides in the major blood vessels around the heart and within the heart itself. They breed and multiply within the heart, and release infectious larva into the bloodstream. It can cause major heart and lung problems, as the worms grow and fill the heart and vessels. It can be very hard and take a long time to treat and cure, with very serious potential complications. Testing is inexpensive and easy, with just a small amount of blood being tested to look for larva. Yearly testing is highly recommended for all dogs over the age of 6 months and is required to receive a prescription for heartworm prevention. Heartworm prevention is available for dogs in both topical and oral formulations and often prevents other internal and external parasites, such as fleas, roundworm, and mites. While heartworm historically is rare or absent in southwestern Ontario, it is on the rise as hotter temperatures are encouraging the breeding and proliferation of mosquitos, and the disease spreads from the United States, where it is much more common.

What are the symptoms of heartworms in a dog?

Since the worms reside in the heart and major vessels around the heart and lungs, the symptoms are often related to these organs. They include coughing, resistance or inability to exercise for long, fatigue, weight loss and occasionally loss of appetite. These symptoms often get worse as the disease progresses, and will eventually lead to heart failure, but it is possible to have little to no symptoms for a long period of time; this is why it is important to test your dog yearly to catch the disease in its early stages.

How do dogs get heartworm?

Heartworm is a parasite carried through the bite of the common mosquito. After the mosquito bites an infected animal (which can include domestic dogs, foxes, coyotes, and wolves), it carries the blood with the heartworm larva in its body. The larva enters the bloodstream when the mosquito bites a second animal, and the larvae are transferred into the bloodstream. They then grow and once adults, reside in the heart and major blood vessels around it to start creating larvae of their own.

What are the treatment options for heartworms?

The current treatment protocol for heartworm involves two months of heartworm preventative and antibiotics to kill the immature worms and prevent worsening of the disease. Then, three injections of an adulticide called melarsomine are given over the course of one month to kill the adult worms in the heart. The dog must be in the hospital for monitoring for these injections since complications can arise as the worms die and travel throughout the body, through the blood vessels. After the treatment is finished, rechecks and testing for heartworms and their larvae must occur before the patient is considered cured. The entire process takes about 9 months.

In rare cases, surgery to remove the worms directly from the heart and major blood vessels can be performed.

Why is recovery and heartworm treatment challenging?

Throughout the entire treatment process, the pet must be kept calm and activity restricted. Keeping the animal in a small room or even crated at all times may be necessary, as increased activity, heart rate, or breathing rate can increase damage to the heart and major blood vessels. Short, leash-only walks are also required, as is keeping the dog out of hot temperatures. This must continue throughout the treatment process, and up to 2 months after the last adulticide injection, which means about 5 months of these new restrictions!

Serious complications are also possible due to the death of the parasites in the heart and bloodstream. The body can overreact to these “foreign invaders,” which is why antihistamines and steroids are often prescribed. The deceased worms can also block blood vessels that lead to the lungs, which can be life-threatening. This is the reason very strict exercise restrictions are put in place, as it greatly reduces the risk.


Order Early Before Holiday Closures

With warm wishes, Your dedicated team at North Town Veterinary Hospital

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North Town Veterinary Hospital is committed to doing everything possible to combat the COVID-19 (coronavirus) outbreak.

As part of this commitment, effective immediately, North Town Veterinary Hospital will be instituting the following precautionary protocol to minimize the risk of COVID-19 transmission.

For the safety of yourself, our staff, and the community we are limiting the amount of clients permitted inside of our building. We have initiated a semi- open door policy to allow one person inside the hospital while your pet is here for a scheduled exam. One person is also permitted inside the hospital for surgical drop offs. Our emergency services remain closed door to clients as our building does not allow for proper social distancing while waiting for the veterinarian. Please call 905-451-2000 when you arrive for your appointment, surgical drop off or emergency service to gain further direction from one of our team members. You can also place an order for pet food through our Online Store by visiting our website.


- If possible, please call us at 905-451-2000 to let us know you are on the way so that we can be prepared to meet you upon your arrival at the hospital.

- When you arrive, please stay in your vehicle in our parking lot and call 905-451-2000, and we'll come to you.

- If you do not have a phone or your pet's emergency is immediately life-threatening, please come to the front door and ring the bell.

Thank you in advance for your understanding.