9 Surprising Things You Didn’t Know About Heartworm Disease

The landscape of heartworm disease is rapidly changing, and it can be hard to keep up. That’s why we’ve put together a list of old ideas about the disease that new information is challenging. We’re committed to bringing you the latest heartworm disease information to help you do the right thing for your pet.

Myth #1: You only need to give heartworm preventive in the summer

Fact: While risk of heartworm transmission decreases in the winter months, complex microenvironments that exist in urban areas mean the risk is never zero. Heartworm preventive should be given year-round.

Myth #2: Heartworm disease doesn’t exist in northern states

Fact: Heartworm infection has been diagnosed in all 50 states. Each year, every Massachusetts veterinary clinic diagnoses an average of 6 to 25 heartworm cases. Environment and climate changes, relocation of heartworm-positive dogs, and expansion of territory of infected wild canids all contribute to spreading heartworm disease.

Myth #3: Heartworm preventives aren’t safe or effective

Fact: Preventives used as directed are incredibly effective and among the safest medications used in veterinary medicine. An animal can become infected from a single missed or delayed dose of preventive.

Myth #4: Indoor cats don’t need heartworm preventive

Fact: Indoor cats are vulnerable to heartworm infection, especially in high-risk areas because no home is immune from infected mosquitoes coming inside. Cats are more likely than dogs to die from heartworm infection because  infected cats typically show only mild symptoms before a fatal reaction. In addition, no good treatment options are available for heartworm-positive cats, and preventive medication is the only way to keep them safe.

Myth #5: Testing isn’t required for animals on heartworm preventive

Fact: Current American Heartworm Society recommendations include:

  • Annual screening for all dogs over 7 months of age with both an antigen and a microfilaria (larva) test
  • Testing any time a dose of preventive has been missed or delayed, with another test in six months
  • Yearly testing for dogs on year-round preventive because of the risk of false-negative results, issues with dose administration, and the (low) risk of infection with resistant heartworms

Myth #6: A negative heartworm test means that the animal is 100% free of heartworms

Fact: Most heartworm tests rely on antigens, or the product of the body’s immune response. However, these tests detect only female adult worms. False-negative tests can occur with a small number of worms, when female worms are immature, or when only male worms are present.

Myth #7: Heartworm disease is fatal

Fact: Prompt heartworm treatment is almost always successful for dogs. Exercise restriction during treatment is paramount because a direct correlation exists between exercise and death during treatment. Other factors affecting outcome include worm numbers, immune response, and infection duration.

Myth #8: Prevention isn’t required because animals will show symptoms of infection

Fact: Animals may be heartworm-positive but show only mild symptoms, or no symptoms. In dogs, worm burden, health, age, and activity level affect whether they’ll show any symptoms. In cats, sudden death could be the first sign of infection.

Myth #9: Only dogs and cats are at risk of developing heartworm disease

Fact: Ferrets are also vulnerable to heartworm infection. Because they are small, even an infection caused by only a few worms can be detrimental to their health.

There are several options that prevent heartworm disease, including some that also treat infection from these other worms and pests:

  • Hookworms
  • Roundworms
  • Tapeworms
  • Whipworms
  • Fleas
  • Ticks
  • Ear mites
  • Sarcoptic mites

Heartworm disease treatment is not easy, but most dog owners find it manageable. Treatment begins with 60 days of antibiotic therapy to reduce side effects and begin killing the worms. Then, medication injections are given 30 days apart to kill adult heartworms. Exercise restriction during treatment is vital, because exercise increases the likelihood of dying worms lodging in the lungs. Surgical removal may be necessary if a dog has a heavy worm burden.

Schedule an appointment at our clinic today to keep your beloved pet free from this terrible, but preventable, disease.