Heartworm in dogs is a serious and potentially fatal disease caused by parasitic worms that live in the heart and lungs. In this article, we will explore how dogs get heartworm and provide information on heartworm prevention for dogs.

How do dogs get heartworm?

Dogs get heartworm from the bite of an infected mosquito. When a mosquito carrying heartworm larvae bites a dog, the larvae enter the dog's bloodstream and migrate to the heart and lungs. Over time, the larvae grow into adult worms that can be up to 12 inches long. Adult heartworms cause damage to the heart, lungs, liver, and kidneys, which can lead to serious health problems and even death.

What are the symptoms of heartworm in dogs?

The symptoms of heartworm in dogs can vary depending on the severity of the infestation. In the early stages of the disease, dogs may show no symptoms at all. As the infestation progresses, dogs may experience coughing, fatigue, weight loss, and difficulty breathing. In severe cases, heartworm disease can lead to heart failure and death.

Is there a test for heartworm in dogs?

If you suspect that your dog may have been exposed to heartworm or if you live in an area with a high incidence of heartworm, your veterinarian may recommend a simple blood test to check for the presence of heartworm antigens. This test can detect the presence of adult heartworms in the bloodstream, and is highly accurate. If the initial test is positive, additional testing may be recommended to confirm the diagnosis and assess the severity of the infestation. It is important to confirm your dog's heartworm status before starting any preventive medication or treatment. Regular testing is also recommended for dogs on preventive medication to ensure that they remain free of heartworm infection.

Do we have heartworm in Canada?

Yes. Heartworm occurs in warmer regions, where summer temperatures are high enough for the worm larvae to survive inside the carrier mosquitoes. The high-risk areas in Canada are southern Ontario, southern Quebec Manitoba, and the Okanagan in British Columbia. Heartworm is also found in most states in the US.

Although it is not absolutely certain, it appears that heartworms are unable to survive at prevailing temperatures in Alberta and Saskatchewan. A few cases are diagnosed in these provinces every year, but to date they have all been dogs that have visited or lived in heartworm risk areas.

The risk of heartworm, both canine and feline, can be checked by visiting the Companion Animal Parasite Council’s Parasite Prevalence Map. 

The greatest numbers of cases are seen in the southeastern U.S. and the Mississippi River Valley. However, cases are appearing with increasing frequency in traditionally low prevalence areas such as California, Oregon, Washington and Colorado.

Preventing heartworm in dogs

Preventing heartworm in dogs is much easier and safer than treating the disease. Here are some steps you can take to protect your dog:

1. Use heartworm preventive medication: Your veterinarian can prescribe a monthly heartworm preventive medication that is safe and effective. These medications work by killing the heartworm larvae before they have a chance to develop into adult worms.
2. Minimize mosquito exposure: Mosquitoes are the carriers of heartworm, so minimizing your dog's exposure to mosquitoes is important. Keep your dog indoors during peak mosquito hours, which are typically dawn and dusk. Use mosquito repellent products designed for dogs when your dog is outdoors.
3. Get your dog tested: Even if your dog is on a heartworm preventive medication, it's important to have them tested annually. Early detection of heartworm is key to successful treatment.
4. Keep your dog healthy: A healthy immune system can help protect your dog from heartworm. Make sure your dog is up to date on all vaccinations and has regular checkups with their veterinarian.

Heartworm in dogs is a severe illness that can be fatal if left untreated. Fortunately, there are straightforward measures you can take to prevent it. By administering a monthly heartworm preventive medication, minimizing your dog's exposure to mosquitoes, ensuring your dog receives annual heartworm testing, and maintaining your dog's overall health, you can safeguard your beloved pet from this potentially deadly disease.

Can my cat get heartworm?

While heartworm is more commonly found in dogs, cats can also become infected. It is therefore recommended that cats traveling to high-risk areas during mosquito season receive preventive medication. Fortunately, there are heartworm tests and medications available that are specifically designed for cats. Be sure to discuss any concerns you may have about heartworm with your veterinarian.