Heartworm disease is one of the most common, deadly, yet easily preventable diseases in dogs and cats. The best way to avoid the high cost of treatment is by following your veterinarian’s recommendations for prevention and routine testing.

What causes heartworm disease?

Heartworm disease occurs when 12-14 inch-long worms live in the heart, lungs and blood vessels, and it all starts from a single mosquito bite!

When a mosquito takes a blood meal from an animal with heartworms, it ingests baby heartworms (microfilaria) present in the infected animal’s blood and becomes a vector of transmission. During the next 10 to 14 days, the microfilaria develop into larvae inside the mosquito. When the mosquito bites another dog or cat, the larvae are transmitted to that animal. From there, it takes about six months for the larvae to turn into adult heartworms while traveling from the skin to the bloodstream before finally reaching the heart.

Heartworm disease in puppies and adult dogs

Unfortunately, dogs, and especially puppies who are not yet on preventives, are the natural host for heartworms.

As adults, the heartworms continue to mate, sometimes producing hundreds of worms. In dogs, the average heartworm can live five to seven years. Infected dogs may have 25-50 heartworms at any given time. The blood vessels that typically carry oxygen-rich blood throughout the body are now clogged with worms!

In the early stage of heartworm infection, dogs may either show no symptoms or the following sign(s):

  • Cough
  • Reluctance to exercise (exercise intolerance/getting tired more easily)
  • Lethargy (not wanting to do their daily routine or play)
  • Decreased appetite

Your veterinarian can perform a blood test to determine if your dog is heartworm positive. This is generally done at your dog’s annual checkup. It’s worth noting that it takes about six months after infection for a test to show up positive, so if your pet was exposed last month the test will not be accurate.

As the number of heartworms increase in the heart, lungs and blood vessels, they block the blood flow to the heart. This may lead to a life-threatening condition is called Caval Syndrome which results in the following signs:

  • Labored breathing
  • Pale gums
  • Severe lethargy
  • Weakness
  • Death

Heartworm disease in cats

Cats, on the other hand, are not the preferred host for heartworms. With that said heartworms and other parasites can impact indoor cats just as much as outdoor felines. A whopping 27% of cats with heartworm disease are indoor cats. In heartworm endemic areas, feline heartworm disease is more common than both feline leukemia and feline immunodeficiency virus (FIV).

Heartworms behave differently in a cat’s body; they rarely grow into adults and produce larvae. Instead, cats typically will host only 1-3 heartworms, but that’s still enough to cause damage. Heartworms cause a condition known as Heartworm Associated Respiratory Disease (HARD) in cats and the signs include: 

  • Coughing
  • Asthma-like symptoms (wheezing, difficulty breathing)
  • Intermittent vomiting
  • Seizures
  • Collapse
  • Sudden death

Ten to twenty percent of cats with adult heartworms will die from this disease, so prevention is critical.

Average costs of heartworm disease medication

Heartworm treatment for dogs typically consists of several medications including multiple injections that require hospitalization and nursing care, costing an average of $400-$1000!*

For cats, the news is worse: The medication used to treat heartworm in dogs is not safe for them and currently, there are no alternatives.

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Common heartworm disease treatment costs:

Sick visit: the exam fee, recheck exam fees

These fees can range from $45-$100 per exam

Diagnostic tests: blood work, radiographs, ultrasound, echocardiogram

Expect to pay $150-$500 per diagnostic test

Treatment: pain medication(s), antibiotics, anti-inflammatory medicines, sedatives, heartworm preventive medications, heartworm treatment medication (dogs only), hospitalization and nursing care

On average expect costs between $300 and $600 per visit

Average costs of heartworm preventive medication

The American Heartworm Society recommends routine testing every year. This generally happens at your pet‚Äôs annual check-up ‚Äď it‚Äôs an important part of their preventive and wellness care.

Also, protect your pet with heartworm preventive medication all 12 months of the year. Talk to your veterinarian about a preventive method (oral, topical or injectable) that fits your pet’s needs and is convenient for your schedule. Pet parents can expect to pay an average of $5-$20 per month (or about $60-$125 every year) for most types of heartworm preventive medication such as Heartgard, Interceptor or Revolution.

Heartworm disease has been diagnosed in all 50 states as well as Canada, affecting more than 1,000,000 pets!** According to the 2019 AHS Heartworm Incidence Survey, the five states with the highest incidence of heartworm were:

  • Mississippi
  • Louisiana
  • South Carolina
  • Arkansas
  • Alabama

Does pet insurance cover heartworm disease?

No, pet insurance does not cover heartworm disease because it is 100% preventable. Heartworm disease treatment has a high financial and emotional cost. Opt for veterinary recommended heartworm prevention to keep your pets disease-free.

* According to Petplan claims data.

**American Heartworm Society

Apr 7, 2020
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