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Heartworm Disease: Awareness and Prevention during American Heart Month

February is American Heart Month, and here at Animal Allies, we know that when it comes to the health and well-being of your pets, being aware of risk factors is key to preventing illness and disease in your pets. Beyond caring for your own cardiovascular health this month, take a few minutes to learn how you can prevent or address heartworm disease in your pet. 

What is heartworm disease?

If you’ve lived in Minnesota for any amount of time, you're probably all too familiar with the state’s seasonal “state bird”–the mosquito. Believe it or not, according to the CDC, the mosquito is one of the world’s deadliest animals. With over 3,700 types of mosquitoes on the planet, the mosquito has killed more people than any other creature in the world. 

Mosquitoes are responsible for carrying diseases and passing them on to people and animals. One mosquito-borne disease that can be transmitted to dogs, cats, coyotes, beavers, horses, and even humans is heartworm disease.

Heartworm disease is a serious disease primarily found in dogs. For the disease to develop, a female mosquito infected with the larvae of a parasitic worm bites a host and infects them with parasitic worms. These worms, known as Dirofilaria immitis, can live in a dog’s heart, lungs, and blood vessels. When heartworms are released into a dog’s bloodstream, they mate, reproduce, and grow in length, ultimately leading to lung disease, heart and organ damage or failure, and even death. It is incredibly important that heartworm-positive dogs limit their physical activity because exercise will increase their heart rate and increase the internal damage caused by heartworms.

It takes approximately six to seven months for a heartworm larva to develop into an adult within a dog. As the heartworm progresses in its growth, it takes on the appearance of a cooked spaghetti noodle. Male heartworms can grow up to six inches in length, while females can grow up to 12 inches. Each heartworm has a lifespan ranging from five to seven years. Although the average number of heartworms present in an infected dog is around 15, as many as 250 heartworms can coexist within a dog that has tested positive for heartworm infection.

How and when should a dog be tested for heartworm disease, and when should prevention start?

It is recommended that dogs aged seven months and older get tested for heartworms before beginning heartworm prevention. To test for heartworms, a veterinarian will use blood tests to determine if a dog has been bitten by an infected mosquito. However, it takes about five to six months for heartworms to be detected after a dog has been bitten. 

Animal Allies’ Practice Manager, Kelsey Pettit, advocates for heartworm prevention beyond monthly heartworm testing. She writes, “While giving a monthly heartworm preventative is the ultimate way to prevent heartworm disease, a proper flea and tick protocol should be employed for all animals that go outside (including cats, who can also be exposed to heartworm and Lyme disease). Many herding breeds can actually have a life-threatening allergic reaction to ivermectin (the main ingredient in HW preventatives). 

“Most vets these days will do a genetic test prior to starting these breeds on a heartworm preventive, which is good. However, this can become complicated with shelter dogs of unknown lineage, so advocating for your pet's safety and educating yourself if you suspect a possible MDR1 mutation is important. Preventing your pet from being bitten is the first, and sometimes only, defense for insect-vector diseases. This also helps with the prevention of tick-borne illnesses, most of which are actually not curable, such as Lyme disease--and can be deadlier than heartworm, like Ehrlichia.” 

What symptoms should I be looking for in my dog? Is heartworm disease curable?

Dogs infected with heartworms are rated based on the four classes of heartworm disease. A dog with a Class 1 infection is characterized by having no symptoms or an occasional cough. In Class 2, the dog suffers from fatigue following light activity. A dog with a Class 3 infection will appear sickly and suffer from advanced cough and fatigue. Finally, a dog suffering from a Class 4 infection, also known as caval syndrome, requires immediate surgery due to restricted blood flow from the heart. Caval syndrome is typically fatal for dogs. 

Thankfully, according to the American Heartworm Society, the majority of dogs with heartworm can be successfully treated. “The goal,” writes the Society, “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.” 

The American Heartworm Society encourages pet owners to “Think 12” by giving their dogs 12 months of heartworm prevention and getting them tested for the disease every 12 months.

Can dogs get heartworms in Minnesota?

Despite the state's notoriously cold weather, yes, dogs can get heartworms in Minnesota.

Though cases of heartworm disease are mostly recorded along the southern and eastern coasts, the Mississippi River, and the Mississippi’s major tributaries, heartworms have been found in dogs all across the United States.

In fact, data from the American Heartworm Society published in 2019 shows that there were about 6-25 cases of heartworm disease per clinic in Minnesota. Animal Allies does receive heartworm-positive dogs, but they are rarely local dogs; typically, heartworm-positive dogs are transferred into the shelter from more southern parts of the country.

Protect your pets this Heart Health Month--start heartworm disease prevention now!

American Health Month prompts pet owners and pet lovers to recognize the seriousness of many serious heart conditions. Though heartworm disease can be a scary diagnosis, testing, prevention, and following your veterinarian’s directions remain the best approaches for keeping your pets safe and healthy. Thank you for being committed to your pets’ health and wellness this month and every month!



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