Heartworm is not lovely!

Let’s start with the first question everyone should be asking.

What is heartworm?

Heartworm is caused by a parasite called Dirofilaria Immitis. These worms can grow to 6-12 inches in length and live in the pulmonary arteries of the lungs in both dogs and cats, ferrets and other wild animal species. Heartworm disease is a very serious and potentially fatal disease causing lasting damage to the heart, lungs and arteries, and can affect the pet’s health and quality of life long after the parasites are gone. The dog is a natural host for heartworms, which means that heartworms that live inside the dog mature into adults, mate and produce offspring (called microfilaria). If untreated, their numbers can increase, and dogs have been
known to harbor several hundred worms in their bodies.

What are the conditions for these worms to live near you?

  • Types of mosquitoes capable of carrying larval heartworms must be present.
  • The weather must be warm enough to allow heartworm larval development within the mosquito. (14°C for everyday for 3-4 weeks. If this temperature drops the larva will die instead)
  • There must be infected dogs or coyotes in the area.
  • There must be vulnerable host dogs in the area.

How does my dog get heartworm?

After meeting the conditions the mosquito plays an essential role in the heartworm life cycle. Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microscopic baby worms called microfilaria that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite wound. This is why it needs to be humid outside, so the saliva drop does not try up. Once inside a new host, it takes approximately 6 months for the larvae to develop into sexually mature adult heartworms. Once mature, heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

Do we have heartworm in Canada?

As of right now, yes we do have heartworm in Canada. As it needs such warm temperatures to stay prevalent you will hear more about in places such as southern Ontario, Southern Quebec, Manitoba, and Okanagan BC. This does not mean that it will never be in any other provinces. With weather changes and things like that it just means we should take precautions and be prepared so it does not become a huge risk.

How do I get my pet tested and when?

Heartworm disease is a serious, progressive disease. The earlier it is detected, the better the chances the pet will recover. If you want to get your friend tested for heartworm the best way to do this is bring them to your veterinarian and they can do a test with a small sample of blood with a SNAP test as well as looking under the microscope for microfilaria and it works by detecting the presence of heartworm proteins. Some veterinarians process heartworm tests right in their hospitals while others send the samples to a diagnostic laboratory. In either case, results are obtained quickly. If your pet tests positive, further tests may be ordered.

When should I get my pet tested?

This does not necessarily mean you should go out and rover tested just because either. The times you would want to see about being tested would be if you just got your new friend from a warmer climate or if you travel to a warmer climate for a longer period of time. If you meet this criteria with your friend then you would want to get tested about 6-7 months after they were last in a warmer climate, be it you coming home or arriving to live in the colder area. However, puppies under 7 months of age can be started on heartworm prevention without a heartworm test (it takes at least 6 months for a dog to test positive after it has been infected), but should be tested 6 months after your initial visit, tested again 6 months later and yearly after that to ensure they are heartworm-free.

Adult dogs over 7 months of age and previously not on a preventive need to be tested prior to starting heartworm prevention. They, too, need to be tested 6 months and 12 months later and annually after that.

The reason for re-testing is that heartworms must be approximately 7 months old before the infection can be diagnosed.

What signs should I look for with heartworm?

  • Coughing
  • Shortness of breath
  • Easy tiring/Exercise intolerance
  • Fluid Accumulation
  • Nosebleeds

Sometimes you won’t notice any of these symptoms in the early stages of the disease. The longer the infection persists, the more likely symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with other health problems often show pronounced clinical signs. Signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As heartworm disease progresses, pets may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen. Dogs with large numbers of heartworms can develop sudden blockages of blood flow within the heart leading to a life-threatening form of cardiovascular collapse.

Can I prevent this?

The best way to prevent this worm from trying to get too close to your furry friend is to stay on a heartworm prevention all year around. Now you may be saying well my temperatures don’t get this warm so why should I worry. While you may be correct and our temperatures in Nova Scotia are harder to stay up and the type of mosquito is not currently in Nova Scotia, but things happen and change rather quickly. We are seeing more and more dogs flown in from warm climates who are testing positive for heartworm. This is a step closer to having heartworm in our area so it is always best to take precautions before something happens. Heartworm products work by wiping out the L3 and L4 stage larvae.

What do I do if we find out Rover is heartworm+ ?

No one wants to hear that their dog has heartworm, but the good news is that most infected dogs can be successfully treated. The goal is to first stabilize your dog if he is showing signs of disease, then kill all adult and immature worms while keeping the side effects of treatment to a minimum.

Here’s what you should expect if your dog tests positive:

Confirm the diagnosis. Once a dog tests positive on an antigen test, the diagnosis should be confirmed with an additional—and different—test. Because the treatment regimen for heartworm is both expensive and complex, your veterinarian will want to be absolutely sure that treatment is necessary.

Restrict exercise. This requirement might be difficult to adhere to, especially if your dog is accustomed to being active. But your dog’s normal physical activities must be restricted as soon as the diagnosis is confirmed, because physical exertion increases the rate at which the
heartworms cause damage in the heart and lungs. The more severe the symptoms, the less activity your dog should have.

Stabilize your dog’s disease. Before actual heartworm treatment can begin, your dog’s condition may need to be stabilized with appropriate therapy. In severe cases of heartworm disease, or when a dog has another serious condition, the process can take several months.

Administer treatment. Once your veterinarian has determined your dog is stable and ready for heartworm treatment, he or she will recommend a treatment protocol involving several steps. The American Heartworm Society has guidelines for developing this plan of attack. Dogs with no signs or mild signs of heartworm disease, such as cough or exercise intolerance, have a high success rate with treatment. More severe disease can also be successfully treated, but the possibility of complications is greater. The severity of heartworm disease does not always correlate with the severity of symptoms, and dogs with many worms may have few or no symptoms early in the course of the disease.

Test (and prevent) for success. Approximately 9 months after treatment is completed, your veterinarian will perform a heartworm test to confirm that all heartworms have been eliminated. To avoid the possibility of your dog contracting heartworm disease again, you will want to administer heartworm prevention year-round for the rest of his life.

Written by: Ashley Goss, VT & Sam M, RVT

Heartworm Society
Veterinary Partner – Heartworm: The Parasite
Veterinary Partner – Canine Heartworms and Preventing Disease
Veterinary Partner – Heartworm Treatment for Dogs