A heartworm infection is a potentially fatal disease that can lead to numerous health complications for your pet, which is why our healthcare team emphasizes a monthly heartworm preventative as part of our patient’s comprehensive care plan. Since heartworms are transmitted through mosquito bites, year round prevention is very important in Florida.

Early detection is critical to the successful treatment of heartworm disease and your pet’s long term recovery. Edge Animal Hospital recommends an annual heartworm test for all of our patients to ensure their preventative medicine is effective, and so that we may diagnose an infection in the early stages when treatment methods are less invasive and less costly to owners.

How are heartworms transmitted?

Mosquitoes ingest immature heartworm larvae, called microfilariae, by feeding on either an infected cat or dog. The microfilariae develop further for 10 to 30 days in the mosquito's gut and then enter parts of the mosquito's mouth. Heartworms are then transmitted by the infected mosquito to our pets through their bites, which inject the larvae into the cat or dog’s bloodstream. 

Heartworm Life Cycle

The larvae then mature over a period of several months, eventually ending up in the right side of the heart and the pulmonary arteries. Once this occurs, they mature into adult heartworms in dogs, and can reproduce about six months from the time of invasion. Approximately eight months after the invasion, the heartworms begin to produce a new crop of microfilariae that will live in the dog or cat’s blood for about one month. By the time this occurs, most patients will show significant heartworm symptoms.

Can indoor cats get heartworms?

While heartworm disease is more often commonly diagnosed in dogs, cats can become infected too. Just like with dogs, the risk of contracting cat heartworm disease exponentially increases without preventive medication. Currently, there are no viable heartworm medicines available for cats that can fight an active infestation - making heartworm disease even more dangerous for cats. 

While sudden death is possible, it isn't common. If your cat is diagnosed with heartworm they may still live a long life under the supervised medical care and treatment of your veterinarian. This may include anti-inflammatory treatments and medications to aid in breathing, similar to those used to treat asthma.

How effective is heartworm prevention?

Fortunately, heartworm disease can be avoided in both dogs and cats with a preventative medication. It is important to consult your veterinarian when making preventive care decisions for your pet for a variety of reasons. For one, there are many over the counter products on the market today that range from ineffective to outright dangerous. Our veterinarians are trained and qualified to help you make the best decisions regarding preventive care and treatment of any health conditions your dog may develop, especially when it comes to parasitic infections.

What are the signs of heartworm disease?

Heartworm symptoms are divided into four stages. It is important to understand that individual stages are not always clearly identifiable and some stages can overlap, but the following information will help educate you about the four major stages, as well as their accompanying heartworm symptoms. 

  1. The first stage is generally symptom free as the heartworms settle into the heart and begin to reproduce. 
  2. The second stage is accompanied by moderate symptoms including intolerance for exercise and a more lingering cough. The heartworms have been present long enough in the body for antibody production and probable microfilariae production. During this phase, heartworm disease may be detected with blood tests.
  3. In the third stage, symptoms including fatigue, coughing, or difficulty breathing will become increasingly noticeable.
  4. Stage four of heartworm disease presents very visible heartworm disease symptoms, accompanied by long-term implications on their health. Even with treatment, this stage of the disease carries a high risk of long term debilitation and possible death.

The four clinical stages of heartworm begin only after the infection has spread into the heart, which is why early detection through annual testing is so important.

How do you test for heartworm disease?

A blood test is performed to detect the presence of adult heartworms. Keep in mind that it takes 6 months from the bite of a heartworm infected mosquito before the disease is detectable with a blood test. If the blood test comes back positive, then the following tests can be performed to determine the stage and severity of the disease in order to determine the most appropriate treatment plan. If there is a positive hw test, we typically recheck the test for verification and test for presence of microfilaria as the next steps (per the American Heartworm Society Protocol)

  • A urinalysis, or the testing of the patient’s urine.
  • A general comprehensive blood panel is performed to assess organ function.
  • Radiographs, or X-Rays to view the size and shape of the patient’s heart. This is helpful because many dogs with heartworm develop enlarged pulmonary arteries, or have obstructions in the arteries leading to the lungs.
  • An ultrasound may be recommended which allows us to directly view the internal structures of the heart and surrounding vessels, in order to assess the condition and function of the heart.

How is heartworm disease treated in dogs?

The first thing to understand is that there is a significant difference between heartworm prevention and heartworm treatment. Prevention is simple to do and is effective in protecting your dog from heartworm disease. Treatment options are used for dogs that are already sick because they have become infected.

The treatment protocol is complicated, but consists of three injections utilized to kill the adult heartworms. Typically, the dog is put on microfilaricide first to control the microfilaria and an antibiotic, doxycycline is administered daily for the first 30 days of the treatment protocol. The first injection is not actually administered until 60 days after starting the American Heartworm Society treatment protocol and hospitalization is required for monitoring. The second and third injections are then administered 30 days after the first, and given one day apart. 

For more severe cases, such as dogs experiencing thromboembolic complications (in which a blood clot that has formed breaks loose and travels through the bloodstream to clot another vessel), hospitalization may be necessary for a longer period of time while heartworm treatments are administered. In some extreme cases, a surgical procedure may be necessary to remove adult worms from the right heart and pulmonary artery by way of the jugular vein. This procedure is recommended if the infestation consists of a high number of adult worms.

Exercise restriction is EXTREMELY IMPORTANT during the entire treatment process to reduce risks of thromboembolic complications.

For more information about heartworm disease, please visit: https://www.heartwormsociety.org/