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Heartworm Awareness Month—Keeping Your Pets Healthy

Ziggy wants to make sure your pet is on heartworm prevention!!!

Unless you’re a veterinarian, the name Dirofilaria imitis might sound unfamiliar to you, but the health of your pet may depend on your understanding of this common parasite. D. imitis is the Latin name for heartworm, a parasitic worm that affects the health of thousands of pets annually—including dogs, cats, and ferrets—and even some wild animals like foxes and wolves. If left untreated, the effects of heartworm can be dangerous and potentially fatal to your pet.

To help raise awareness of heartworm disease and to promote early diagnosis and treatment, April has been designated National Heartworm Awareness Month. The American Heartworm Society urges all pet owners to educate themselves on heartworm prevention to help reduce the number of cases seen in the U.S. annually.

What Exactly is a Heartworm?

Heartworms are parasitic organisms that can reach 10–12 inches in length. These worms live within the chambers of the heart, as well as within the adjacent blood vessels. An individual worm can survive 5–7 years. Heartworms reproduce within the host animal, and a single dog can host up to 250 worms. Over time, the worms impair heart and lung function, and in severe cases, can result in death.

Cats become infected by heartworms the same way dogs do: through the bite of a hungry, infected mosquito. Many pet owners are surprised to learn that about a third of heartworm-infected cats are indoor cats. Think of how easily a mosquito can enter your home –  through an open door as you enter or leave, or a small tear in a window screen. How many times have you swatted at a mosquito inside? Though your cat may be an indoor cat, that does not make her immune to heartworm disease.

Cats must be bitten directly by a heartworm-infected mosquito; heartworm cannot be transmitted from one cat to another, or from a dog to a cat. When mosquitos land on a cat and have a blood meal, they insert their sharp mouthpieces into the cat’s body. They then deposit microscopic heartworm larvae into the cat’s bloodstream as they feast on the cat’s blood. In dogs, the larvae mature over several months eventually migrating to the heart and lungs. As cats are atypical hosts, many larvae never mature to adult heartworms but they still cause problems. Immature heartworm larvae cause a condition in cats called heartworm associated respiratory disease (HARD). 

Because so few heartworm larvae mature to adults, cats can be particularly difficult to diagnose with heartworm. There are no specific clinical signs in cats, although they may show non-specific signs such as lethargy, lack of appetite or weight loss. The most common sign is the sudden onset of a cough and difficulty breathing, which can often be mistaken for and/or misdiagnosed as asthma (HARD). Sometimes, an apparently-healthy cat may be found dead or develop sudden respiratory failure leading to death, in which case heartworm disease may be diagnosed post-mortem.  

Unfortunately, there is no medication to kill heartworms that is approved or safe for treating cats, as there is for dogs. Treatments are usually supportive, focusing on managing symptoms of the disease and preventing the reproduction of new heartworms. Surgical removal of the worms is possible but is often reserved for cats with poor prognosis without surgery.  

The best way to prevent heartworms in your dog or cat is to give your pet a heartworm preventive. In warmer climates like Florida where mosquitos are active year-round, pets should receive a preventive year-round!

How is Heartworm Transmitted?

Heartworm is a vector-borne disease that is transmitted by mosquitoes. An insect that feeds on an infected animal can then transmit the parasite to an uninfected animal that it bites subsequently. Once the parasite’s larvae infect a new host, it can take about 6 months for heartworms to reach adult, reproductive age.

What Are the Signs and Symptoms of Heartworm?

Early in the disease course, your pet may be asymptomatic, which makes heartworm tricky to diagnose. As the disease progresses, your dog may experience:

  • persistent cough

  • reluctance to exercise

  • fatigue

  • appetite loss

  • weight loss

Some dogs also experience difficulty walking, fainting, seizures, or abdominal bloating. In many cases, however, the disease progresses without producing significant symptoms until its late stage, when a fatality is likely.

In cats, a heartworm can cause:

  • persistent cough

  • asthma-like attacks

  • vomiting

  • loss of appetite

  • weight loss.

How Can You Prevent Heartworm in Your Pets?

If this all sounds pretty scary, it is. Heartworm is a serious condition. Fortunately, there are some steps you can take to help prevent, diagnose, and treat heartworm in your pet.

Get Your Pet Tested

All pets should undergo annual heartworm testing. The test requires a blood sample to conduct an antigen test. This detects proteins produced by the parasite within your pet’s bloodstream. Puppies that are under 7 months of age can be started on a heartworm preventative without the need for a blood test. Dogs older than 7 months should be tested before beginning any heartworm preventive regimen.

For cats, the process is somewhat different. Because heartworms are less common and harder to detect in cats, your vet may use other means, such as x-ray and ultrasound, to detect the presence of the parasite in felines. Blood tests for parasite antigens are also performed in cats.

Heartworm Preventives

A range of prescription heartworm prevention treatments is available. If your pet tests negative, your veterinarian can recommend different products.


If your pet tests positive for heartworm, your vet will likely recommend a treatment course based on the overall condition and health history of your animal. If your pet has advanced heartworm disease, your vet may ask you to restrict your animal’s activity or to administer medications that will stabilize your animal’s condition before heartworm treatment can begin.

To kill adult heartworms, your vet may administer a drug called melarsomine, given by injection at your vet’s office. Subsequent testing will determine the success of the treatment. If the worms are not eradicated, additional treatment may be needed. Remember, there is currently no drug treatment for cats with heartworm disease, and care is largely supportive.


We hope this quick review will help you better understand the importance of getting your pet tested for heartworms. At Companion Veterinary and Urgent Care, we understand how important your pet’s health is to you. Our trained and compassionate staff can help explain the risks of heartworm disease, can conduct heartworm tests, make your pets are on preventatives to protect them year round, and can administer treatment if your pet tests positive for the parasite. Make an appointment today—we’re ready to help!

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