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Heartworm Disease

Heartworm diseaseHeartworm Disease

A single bite from an infected mosquito can put your pet at risk for developing heartworm disease. Even indoor-only pets are at risk for heartworm infection since mosquitoes can find their way inside the home.

This deadly disease has been reported in all 50 states, and our pets depend on us to keep them safe and healthy. The good news is that heartworm disease is highly preventable, and the cost of medication is far less than the treatment. Treating heartworm is up to 25 times more expensive than simply preventing it.

What is Heartworm Disease?

Heartworm, also known as Dirofilaria Immitis, is a serious and potentially deadly parasite that lives in the bloodstream and is passed along to your pet through bites from infected mosquitoes. These parasites are found just outside the heart in the pulmonary arteries, which carry blood to the lungs to get oxygen and deliver it to the rest of the body.

Baby heartworms are passed to your pet when a mosquito bites. Adult heartworms can grow into foot-long worms that infect the heart, lungs, and arteries, causing severe lung and heart disease and damage to other organs in the body.

Initially, these parasites were discovered in the hearts of dogs after they passed away from the disease. When blood stopped flowing through these vessels, the worms fell backward into the heart, giving them the name “heartworms.”

Heartworm Life Cycle

Heartworms are transmitted to our pets by mosquitoes. The mosquito is necessary to complete the life cycle of the parasite. The process from the initial mosquito bite and the injection of immature worms (microfilariae) into the blood of the pet to the development of adult worms can take longer than seven months for the heartworms to be detectable with routine testing. An adult heartworm can grow up to a foot in length, living inside your dog’s heart and lungs.

Understanding the heartworm life cycle is important in testing for the disease. If your pet is bitten and infected in the summertime, a heartworm test may not become positive until the winter or even later.

When a heartworm test is performed using a blood sample, it looks for signs of adult female heartworms. Tests may come back negative, however, despite an active infection with adult worms. This occurs when the adult worms are male, or the females are still too immature to show a positive result.

If your pet does test positive, we may recommend further testing and consultation with a veterinary cardiologist.

  • Additional tests can be extensive and include:
  • Full bloodwork
  • Evaluation of urine
  • Evaluation of urine
  • Echocardiogram or ultrasound of the heart to evaluate the chambers of the heart and vessels and look for the worms themselves

Dogs and Heartworm Disease

Dogs are a natural host for heartworms, meaning that baby heartworms commonly mature into adult heartworms. Heartworm disease causes damage to a dog’s heart, lungs, and arteries that can last long after the heartworms are gone.

Symptoms are caused by the adult worms and vary depending on the number of worms present, which may include:

  • No symptoms
  • Cough
  • Exercise intolerance
  • Difficulty breathing
  • Death

It’s important to get your pet tested for heartworms annually. In some cases, testing needs to be more frequent to properly detect this potentially fatal disease.

Heartworm Treatment in Dogs

Heartworm infection in dogs is treatable and is effective, usually successful. But treatment is complicated with many months of crate rest, and there are risks of complications depending on the damage already done. Prevention is the best option.

Treatment in dogs involves:

  • The use of an adulticide (a drug that kills the adult worms)
  • Microfilariacide (a drug to kill the circulating offspring and immature worms circulating in the bloodstream)
  • Surgical retrieval of the worms under general anesthesia by a cardiologist may be necessary for some dogs with more severe infections involving large numbers of worms.

Adulticide Injections:

  • Given in multiple stages into the muscles of your dog’s back
  • Many dogs are hospitalized during this treatment.
  • Once at home, dogs need to be strictly rested in a cage for at least a month or two to avoid severe life-threatening complications.

Cats and Heartworm Disease

There are currently no safe and effective treatments available for cats with heartworm disease. The only way to protect your cats from heartworm disease is to make sure that they receive their parasite preventative throughout the year, even indoor-only cats, since mosquitoes can get inside your home. One infected mosquito can easily put your cat at risk.

Cats have a different response to infection. In cats, heartworms less frequently grow into adults, BUT it only takes one or two adult heartworms to cause severe damage and even death in cats. Most of the time, there are no symptoms associated with a heartworm infection in a cat. Sometimes, an infected cat may vomit, cough, or have a reduced appetite, while other times, the only sign you’ll see is sudden death.


Prevention is by far the safest and most economical way to protect your pet from this infection. Before starting heartworm preventatives, it is important to have your pet examined and heartworm tested annually during your pet’s regular veterinary visits. There are a variety of effective and inexpensive preventatives for both dogs and cats available; however every pet and every situation are different, so be sure to call us at 813-920-0303 about which option is the best for your pet.

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