Heartworm Prevention: The Key to Saving Your Pet’s Heart

Apr 3, 2020 by

Dog and Cat Laying Down

Our pets play such an integral part in our lives, offering love and friendship through each stage of our journey together. According to a recent research study by the American Pet Products Association, 68% of US households have at least one pet with approximately 90 million dogs and 94 million cats being the primary pets for these owners.

Yet, even with all that dedicated focus on our pets, there are still diseases that have not yet been fully eradicated such as heartworm. As veterinarians, heartworm disease is one of the most difficult to treat, simply because it is preventable in all pets and treatable in dogs. Understanding how heartworms occur, how to prevent them and how to treat them can save your pet from the pain and suffering associated with this deadly disease. 

Sections
Heartworm in Dogs
Heartworm in Cats
Myths and Questions

Labrador Retriever Laying Down

Heartworm in Dogs

Heartworm disease in dogs starts with something extremely common: the bite of a mosquito. This potentially fatal disease can impact dogs, cats, exotic pets such as ferrets and even humans, causing heart failure, severe lung disease and damage to many other organs of the body. These foot-long worms are most likely to be found inside the heart of canines, where they grow, mature and even produce offspring. Over time, the mass of heartworms grows exponentially causing increasing damage to your pet’s heart and reducing their quality of life. 

The Heartworm Lifecycle in Dogs

While heartworm disease is not contagious in the traditional sense, it can be passed from canine to canine, feline or another host. Adult heartworms living within a host release microfilariae into the bloodstream of your pet. These minuscule larvae are the offspring of the heartworm and can be passed to a mosquito that bites an infected pet. This “loaded” mosquito can then bite another pet, transferring the microfilariae into the new dog and beginning the growth cycle of the infected larvae. These microfilariae cannot be transferred directly between hosts, and require passing through a mosquito for 10-14 days to become infective larvae. These larvae are then passed to a new host animal to grow into mature, adult heartworms within six to seven months. When the male and female heartworms mate within their host, the entire heartworm lifecycle begins again.

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While heartworm disease is not contagious in the traditional sense, it can be passed from canine to canine, feline or another host.

How is a Dog Tested for Heartworms?

Unfortunately, it takes an average of 6-7 months or more after infection before heartworm disease can be diagnosed in your dog. Veterinarians utilize a simple blood test that is looking for antigens released by female heartworms into your pet’s bloodstream. A secondary test is available that also looks for the presence of microfilariae in the bloodstream, a sure sign of adult heartworms. 

When Should a Dog Be Tested for Heartworms?

While your veterinarian likely has specific ideas about testing for heartworm disease, general standards indicate that dogs 7 months of age or older should be tested before beginning preventive heartworm medication. There are dangers associated with offering preventive heartworm treatment to animals that may already be infected, as this will not kill any adult heartworms that are present. At a minimum, most veterinarians recommend annual heartworm testing and immediate treatment for any heartworms that are found.

What are the Symptoms of Heartworm Disease in a Dog?

Understanding heartworm treatment in dogs requires first knowing the “worm burden” — or the number of worms that are currently living inside your pet. The severity of the symptoms can vary, with a dog that has a very low worm burden showing limited signs of stress while the damage is more evident for animals with more heartworms or who have been infected for a longer period of time. There are four main stages of heartworm in dogs:

  • Class 1: Limited to no symptoms, which may be as simple as a light cough. 
  • Class 2: You might notice that your pet is more tired than usual after an activity or exhibiting a slightly more regular cough. 
  • Class 3: During this phase of the disease, pets will be more visibly ill and might have a persistent cough and seem much more tired after normal activities. Your veterinarian should be able to see changes to your pet’s heart and lungs via X-ray, and there’s a higher potential for heart failure or difficulty breathing. 
  • Class 4: Also known as caval syndrome, Class 4 heartworm disease is often fatal for your pet. The masses of heartworms have multiplied, effectively blocking the flow of blood back into the heart. Immediate surgery to remove the mass of heartworms is often the only treatment, and it is not always viable. 
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Understanding heartworm treatment in dogs requires first knowing the “worm burden” — or the number of worms that are currently living inside your pet.

Is There a Treatment for Heartworm Disease in Dogs?

Finding a heartworm treatment for dogs isn’t quite as easy as it sounds. There is only one heartworm medication for dogs that has been approved for use: melarsomine dihydrochloride (trade names: Immiticide and Diroban). This arsenic-containing drug is injected deep into the back muscles of your pet and is only used to treat Class 1, 2 or 3 heartworm disease. Unfortunately, this treatment is potentially toxic and can even have life-threatening complications such as blood clots in the lungs. There is a secondary treatment available to eliminate microfilariae that are living in the bloodstream of your pet, called Advantage Multi for Dogs (imidacloprid and moxidectin).

The Best Treatment is Prevention!

While both of these treatments are FDA-approved, the best treatment truly is prevention. Unlike the limited diseases used to treat heartworm disease, there are many more options available to help prevent heartworms from taking hold inside of your pet. There are also delivery options, with everything from oral tablets to topical liquids that are applied to the skin serving as viable options to protect your dog from this painful and life-threatening disease. 

Sick Cat

Heartworm in Cats

Now that you’re well-informed on heartworm in dogs, what about heartworm in cats? According to Dr. Casey from Sunset Veterinary Clinic: “Cats definitely are not exempt from heartworm disease, but the clinical presentations and treatments differ greatly compared to the dog. The cat is not the natural host for the parasite and therefore it becomes more of a lung disease rather than heart disease in cats.” 

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“Cats definitely are not exempt from heartworm disease, but the … treatments differ greatly compared to the dog.” — Dr. Michelle Casey, DVM

What are the Symptoms of Heartworm Disease in Cats?

It can be more difficult to diagnose heartworm disease in cats, as the symptoms may be mild difficulty breathing or wheezing, a soft cough, vomiting, neurological signs and even sudden death. While many cats can clear the infection on their own, the downside is that the same medicine used on dogs to clear heartworms cannot be used on felines.

Are There Treatments for Heartworm Disease in Cats?

“There is no cure for cats at this time. Melarsomine use in cats is very risky and will induce serious side effects. Cats that have heartworms are managed based on their symptoms and starting on heartworm prevention. Luckily for cats, they are not the normal host for these worms and therefore only have 1-3 worms usually. The worms do not live as long in cats as they do in dogs. But they can still cause significant disease and complications including sudden death”, notes Dr. Lucas White from Sunset Veterinary Clinic. Prevention is always the best cure!

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“There is no cure for cats at this time. Melarsomine use in cats is very risky and will induce serious side effects. Luckily for cats, they are not the normal host for these worms and therefore only have 1-3 worms usually. ” — Dr. Lucas White, DVM

Should Cats be Tested for Heartworms?

Absolutely! Having your pets tested on a regular basis allows you to catch early symptoms in time to provide assistance to your pet. As you’ve seen, Class 1, 2 and 3 heartworm disease can be treated with medication — at least in dogs. With cats, your veterinarian is more likely to treat the symptoms than the disease itself, improving the quality of life for your cat. 

Dog and Cat with Veterinarian

Heartworm Myths and Questions

Just as with any complex topic, there are plenty of myths and misinformation floating around in the world! Here are a few common myths and questions (with answers!) from the veterinarians at Sunset Veterinary Clinic

Is heartworm disease contagious for pets?

While it’s not technically contagious from one pet to another, it’s not surprising to find a rash of pets in the same area with heartworms. Since the disease is passed by mosquitos, there is a strong possibility that they will infect multiple pets during the mosquito’s lifecycle.

Is it true that only dogs can get heartworm disease?

Unfortunately, no. Heartworm in humans, cats, ferrets and other animals does occur, but less often than in canines. Cats and other pets are not the preferred hosts for heartworms, making it less likely that the heartworms will grow large enough or in great enough quantities to cause significant problems. 

Do house cats and other indoor pets need heartworm prevention?

Without question! According to Dr. Lucas White, nearly 30% of pets that are diagnosed with heartworm disease are “indoor only” pets. Think about it: mosquitoes sneak into your home — don’t take a chance that they’re carrying infective heartworm larvae!

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“Nearly 30% of pets that are diagnosed with heartworm disease are indoor only pets.” — Dr. Lucas White, DVM

Will heartworms eventually die, so my pet doesn’t really need treatment?

Heartworms will not disappear, and the disease requires intervention for your pets to return to health. When in doubt, reach out to your veterinarians at Sunset Veterinary Clinic with questions!

Can people get heartworms from their pets?

Since heartworms are only transmitted via an infected mosquito, humans cannot contract heartworm disease from their pets. However, people can contract the disease from the bite of an infected mosquito. Fortunately, heartworm larvae rarely survive the trip through the human body. 

Get Help or More Information?

Wondering how you can get more information about heartworm disease and how to protect your pets? Dr. Michelle Casey recommends checking out the American Heartworm Society website. Or feel free any of our veterinarians like Dr. Casey or Dr. White at Sunset Veterinary Clinic at 405-844-2888 to schedule a checkup for your family pets.

Heartworms Infographic

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