Heartworm Quiz: Learn the Facts to Keep Your Pets Safe

Even if your pet never goes outdoors, he can still be bitten by heartworm-infected mosquitoes.

Among the illnesses that affect our pets, few are better known than heartworm disease. And for good reason: Heartworm is potentially life threatening to our pets. But do you truly understand all aspects of this disease — and how to prevent it? To test your heartworm smarts, determine whether the following statements are true or false. You may be surprised by some of the answers.

Take the Heartworm Quiz

TRUE OR FALSE: Cats don’t need heartworm prevention.

FALSE. Heartworms affect cats and dogs differently, but both species need to be on preventive medication. In fact, prevention is especially important in cats, since feline heartworm disease can be difficult to diagnose. Why? Because heartworm-infected cats seldom harbor adult heartworms or their early offspring, known as microfilariae. Detecting the adult worms or circulating microfilariae is the basis for diagnosing heartworm infections in dogs. Although an additional test for cats can detect heartworm-specific antibodies, this test only confirms exposure to heartworm-infected mosquitoes, not an active infection.

To understand how heartworms affect cats — and dogs — it’s important to know the heartworm life cycle:

  • First, an infected mosquito ingests microfilariae circulating in the blood by biting an already infected animal.

  • The microfilariae develop into an infective larval stage inside the mosquito.

  • The infective larvae are transmitted to another animal via a mosquito bite.

  • The larvae migrate to the animal’s heart and pulmonary arteries, where they develop into adult heartworms.

  • The adult female heartworms release microfilariae into the animal’s bloodstream after mating, starting the cycle all over again.
    In cats, many of the larvae never develop into adult heartworms, but instead migrate to the lungs through the pulmonary arteries, where their presence and death cause inflammation. This can cause cats to develop severe respiratory disease, even without worms in their hearts. Respiratory distress, including the coughing and labored breathing that we see in some heartworm-infected cats, can resemble what we see with other feline respiratory or heart diseases, such as asthma, cardiomyopathy (disease of the heart muscle) or bacterial or viral infections that cause pneumonia.

Finally, and most importantly, while we have effective treatments for canine heartworm disease — although they can involve hospitalization and multiple steps, and if not begun soon enough, might not prevent heart and lung complications — these same treatments cannot be used to eliminate adult heartworms in cats.

TRUE OR FALSE: All pets require heartworm prevention — even those that stay indoors.

TRUE. Even though truly indoor pets are less likely than outdoor pets to be bitten by heartworm-infected mosquitoes, indoor pets can still get infected with heartworms. In fact, North Carolina University’s study of heartworm-infected cats revealed that 27 percent of the cats were characterized by their owners as residing entirely indoors.

One reason this misperception continues is that some pet owners think that if their pets live inside, they just cannot be exposed to mosquitoes. However, many pets are allowed to sit or lie near open windows or accompany their owners out on a deck or patio. And let's face it: Most of us have seen mosquitoes inside our homes. Do not allow this myth to be perpetuated. Insist on year-round protection, regardless of your pet’s indoor or outdoor habits. Mosquitoes can sneak inside, so even indoor pets need preventive medicine.