Heartworm Awareness – What You Need To Know

Your pet’s health is important to us, here’s what you need to know about Heartworm Disease.

Learn the facts so we can work together to keep your pet healthy and heartworm-free.

Heartworm disease is a severe and possibly fatal infection caused by parasitic worms residing in cats, dogs and other mammals’ arteries of the lungs and the heart. It can also lead to severe lung disease, heart failure and damage to other body organs. Both cats and dogs are vulnerable to infection.

Although both cats and dogs can get heartworms, they are affected very differently.

Simply put, the dog is a natural host for heartworms, meaning that heartworms living within the dog grow into adults, mate and bear offspring. The Cat, by comparison, is not. They are an atypical heartworm host, and the majority of worms in cats do not survive to adult stage. Cats with adult heartworms typically have only one or three worms, and others do not have adult worms. Although it is generally undiagnosed in cats, it is important to recognize that even immature worms can inflict real damage, possibly leading to a condition known as respiratory disease (HARD) associated with the heartworm.

So to summarize – All Heartworms are bad!

In the United States, Heartworm disease reported mostly in the southern states; 

From the Gulf of Mexico to New Jersey and along the Mississippi River and it’s major tributaries, although there are many cases across the States.

The truth is that heartworm disease is diagnosed in all 50 states, so preventatives should never be based on reported cases in your area. Multiple factors, ranging from climate changes to the presence of wildlife carriers, cause infection rates to vary significantly from year to year even within populations. Both outdoor and indoor pets are at risk since infected mosquitoes may come inside.

So How Do They Get Around?

The mosquito is key in the heartworm life cycle.


Adult female heartworms living in an infected animal produce microscopic baby worms called microfilaria that circulate in the bloodstream.

When a mosquito bites and takes blood from the animal, it picks up these baby worms. They then develop and mature into “infective stage” larvae over a period of 10 to 14 days. When the infected mosquito bites another susceptible animal, the infective larvae are deposited on the surface of the animal’s skin and enter the new host through the mosquito’s bite wound. Once inside a new host, it takes an estimated 6 months for the larvae to mature into adult heartworms.



Adult heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats.

Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

Heartworm disease is spreading to new regions of the country each year. Stray or neglected dogs and certain wildlife such as coyotes, wolves, and foxes can be carriers. Mosquitoes travel great distances by the wind. The relocation of infected pets to previously uninfected areas, also contribute to the spread of heartworm disease. This happened following Hurricane Katrina when 250,000 pets, many of them infected with heartworms, were “adopted” and shipped throughout the country.

Heartworm disease is completely preventable and treatment is safe and inexpensive!

Some treatment options include chewable tablets, topicals or injections. The key is to provide Heartworm preventatives properly and on a strict schedule. As a pet owner, it is your responsibility to maintain the prevention program you select with your veterinarian. Heartworm disease is successfully treated in dogs with proper care, but there is currently no treatment for cats. The cost for treatment varies but can be very costly.

What are the early signs of Heartworm disease?

It is common for Dogs to show little to no symptoms at all. The longer left untreated, the more likely symptoms will develop. Active dogs, dogs with a high Heartworm count, or those with other health problems often show more pronounced symptoms.

The most prominent symptoms are:

  • Weight loss
  • Fatigue after moderate activity
  • Decreased appetite
  • Mild or persistent cough
  • Lethargy or lameness

As the disease grows more intense, your furry friend can quickly go into heart failure and what may seem like a swollen belly because of fluid within the abdomen area. Dogs with larger numbers of heartworms can develop a sudden blockages of blood flow inside the center thus resulting in a life-threatening kind of cardiovascular collapse. You may even notice sudden labored breathing, pale gums, and dark bloody or coffee-colored urine. Without emergency surgical removal of the Heartworm blockage, few dogs survive.

Cats tend to show extremes of symptoms, such as none at all, or all of them dramatically. These symptoms may include:

  • Weight loss
  • Coughing
  • Asthma-like attacks
  • Lack of appetite
  • Vomiting
  • Lameness

They can also have difficulty walking, experience fainting or seizures, or suffer from excess fluid in the abdomen area. Commonly, the first sign in some cases is sudden collapse, or sudden death.

How does testing work?

As you can see, Heartworm disease progresses quietly and quickly.

The quicker we diagnose the disease, the more likely we can effectively treat it. There are few, if any, early signs of disease when a dog or cat is a host, so doing a Heartworm test administered by a veterinarian is incredibly important to your pets health and well-being. Testing and timing differ somewhat between dogs and cats, but general the rule of thumb is to test annually (depending on a few factors).
Adult dogs over 7 months of age and previously not on a preventive need to be tested prior to starting Heartworm prevention.  Then again, they need to be tested 6 months and 12 months later and annually after that. The test requires just a small blood sample from your pet, and works by detecting the presence of heartworm proteins. Our clinic processes heartworm tests in house, so there is no need to wait for results! If your pet tests positive, further tests may be ordered.
If your pet is…
  • Younger than 7 months, they can start on heartworm prevention without being tested. Six months after the initial visit, you would test for heartworms, as it takes 6 months for an infected dog to test positive. Then testing again 6 months later, and then yearly to ensure your pet continues to test negative.
  • Over 7 months old and previously not on a preventive, they need to be tested before heartworm prevention. They then need to be tested 6 months and 12 months later and yearly after that.
  • If there has been one or more late or missed doses of prevention, the pup should be tested immediately. Then tested again six months later and annually after that.
Annual testing is incredibly necessary, even when dogs are on yearly prevention. Heartworm treatment plans are highly effective, but there is still a chance of becoming infected. Missing just one dose of a monthly prevention—or even just giving it late— can leave your dog vulnerable to infection. If you don’t get your dog tested, you won’t know your dog needs treatment.

It is much harder to detect Heartworms in cats than in dogs because they are much less likely to have adult heartworms.

In order to test Cats for heartworms, we have to draw blood for an antigen and antibody test. We may also use x-rays or ultrasound to look for a visual on the possible infection. Just like dogs, cats need to be tested before being put on prevention. Prevention is critical, there is no effective treatment plan for cats.

What kind of treatment plan is there in the case of a positive heartworm test?

The good news is most contaminated dogs can be treated successfully and efficiently with proper care and treatment. The goal is to stabilize your dog as soon as you know they are positive, then kill both adult and immature worms while keeping the treatment’s side effects to a minimum.

What to expect:

  • Confirm. Upon receiving a positive test, the diagnosis should be confirmed with an additional—and different—test. Because the treatment regimen for heartworm is time consuming, expensive, and complex, you will want to be sure that taking action is necessary.
  • Restrict activity. This is the most difficult part of treatment, our clients find. Especially if your dog is highly energetic, or just really loves playtime. But their normal activities must be restricted as soon as the diagnosis is confirmed, because physical exertion increases the rate at which the heartworms cause damage in the heart and lungs. The more severe the symptoms, the less excercise your dog should have.
  • Stabilize. Before actual treatment can begin, your pups health needs to be the best that it can be, given the circumstances. Therapy is common with dogs that have other medical conditions unrelated to heartworms. In severe cases of heartworm disease, or when a dog has another serious condition, the process can take several months.
  • Treatment. Once we have determined your pup is stable and ready for treatment, we will recommend a treatment plan with several steps. The American Heartworm Society has guidelines for effective treatment plans. Dogs with none or mild signs of the disease, like cough or exercise intolerance, have a high success rate with treatment. More severe cases can be successfully treated, but the risk of complications is significantly greater. The severity of heartworm disease doesn’t always correlate with the severity of symptoms. Remember, dogs with many worms may also have few or no symptoms early in the course of the disease.
  • Test (and prevent) for a long healthy life. 6 months after treatment is completed, we will test again to confirm that all heartworms are gone. To avoid your dog contracting the disease again, you need to administer heartworm prevention year-round for the rest of his life.

A cat is not an ideal host for Heartworms, some infections can resolve on their own. But in most cases, treatment is still needed to ensure the healing process is done safely.

Respiratory system damage is a big risk in Cats infected with heartworms. They can also affect the immune system and cause symptoms such as coughing, wheezing and difficulty breathing. They may even move to other parts of the body, such as the brain, eye and spinal cord. Blood clots in the lungs and lung inflammation can result when the adult worms die in the cat’s body as well.

What to expect:

  • Diagnosis. Cats almost always have 6 or fewer worms in their body. The severity of the disease in dogs is related to the number of worms, but in cats, just one or two worms can be deadly. Diagnosis is complex, requiring a comprehensive exam, an X-ray, a complete blood count and several kinds of blood test. An ultrasound may also be done.
  • Treatment. There is no approved drug therapy for heartworm infection in cats, and what is used to treat infections in dogs is not safe for cats. Cats with this disease can often be tackled with proper veterinary care. The goal is to stabilize your cat quickly and find a long-term management plan with their veterinarian.
  • Monitor. Cats that have tested positive may experience a spontaneous loss of heartworms, but the damage from this loss may be permanent. If your cat is not showing signs of respiratory distress, but has active worms detected in the lungs, chest X-rays every 6 to 12 months will be recommended. If mild symptoms are found, mediations may be prescribed to help reduce inflammation.
  • Intensive care. If the disease is severe, additional efforts will be made such as hospitalization in order to provide therapy, intravenous fluids, drugs to treat lung and heart symptoms, antibiotics, and general nursing care. Surgical removal of heartworms may be an option if needed.
  • Upkeep prevention. When a cat is diagnosed with this disease, it has shown that it is susceptible to heartworm infection, and both outdoor and indoor cats are at risk. It’s important to give your cat monthly heartworm preventives, which are available in both topical and pill form.
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