Preventing And Treating Heartworms In Cats


At Cat Care Center of Baton Rouge, our highly experienced veterinarian and veterinary support staff have been helping educate our clients on heartworm disease in cats since 2019. The importance of heartworm prevention for cats cannot be overstated. Once a cat has contracted heartworms, it cannot be cured. Therefore, preventive measures are absolutely necessary in order to keep your beloved feline friend healthy and safe.

What Is Dirofilariasis, AKA Cat Heartworm?

Dirofilaria immitis is a blood-borne parasitic nematode (roundworm), commonly referred to as cat heartworm. Heartworms in cats are spread through mosquitos carrying cat heartworm larvae. The severity of heartworm disease in cats is directly dependent upon the number of worms present in a cat's body, the duration of the incubation, and the response of the infected cat.

Although heartworms in felines are less prevalent than in canines, feline heartworms are still a dangerous disease. This disease is very different from heartworm disease in dogs. The cat is not the natural host for this parasite, and most of their worms don't survive to adulthood. Cats usually have just one to three worms at a time, most of which are immature worms. It is because of this that heartworm disease often cannot be diagnosed by a simple heartworm test in the cat. In addition, immature heartworms can cause an intense lung reaction and subsequent disease called Heartworm Associated Respiratory Disease (HARD). The risk of cat heartworm disease is on the rise in America, and about equal for both indoor and outdoor cats. If you do not use preventive medication, the risk of contracting cat heartworm disease exponentially increases. This is why preventive cat heartworm medication is so important.

Symptoms of Cat Heartworm Disease

One of the most challenging aspects of diagnosing heartworms in cats is that there are no definitive clinical signs that directly indicate the existence of cat heartworm disease. However, this doesn't necessarily mean that cat heartworm disease isn't present. Some health signs that might indicate the presence of cat heartworm disease include:

  • Vomiting and coughing are two of the most common symptoms
  • Difficult or labored breathing (Heartworm Associated Respiratory Disease - HARD)
  • Convulsions
  • Blindness
  • Lethargy
  • Anorexia/weight loss
  • Fluid in the lungs
  • Collapse
  • Rapid heart rate
  • Diarrhea
  • Sudden death

On occasion, an apparently healthy cat may be found dead, or may develop sudden overwhelming respiratory failure. In these cases, cat heartworm disease may be diagnosed on a post-mortem examination.

We can easily prevent cat heartworm disease long before serious medical issues or life-threatening emergencies develop by simply implementing preventive measures.

How Are Cat Heartworms Transmitted?

Upwards of 30 species of mosquitoes can act as cat heartworm transmitters. Mosquitoes ingest immature heartworm larvae, called microfilariae, by feeding on either an infected dog, fox, coyote, or wolf. The microfilariae develop further for 10 to 14 days in the mosquito's gut and then enter parts of its mouth.

When an infected mosquito bites a cat, the infective larvae are released onto the skin and enter the cat through the mosquito's bite wound. The larvae then migrate and mature over a period of several months, eventually ending up in the right side of the heart and the pulmonary arteries. Approximately eight months after the invasion, cat heartworms begin to produce a new crop of microfilariae that will live in the cat's blood for about one month. By the time this occurs, most cats begin showing symptoms of cat heartworm disease and it can become fatal very rapidly. Adult heartworms, if they make it to the adult stage by evading the cat's immune system, can live up to 2 or 3 years.

**In many cats the heartworms will not mature past the immature stages due to the intense immune reaction. However, heartworm Associated Respiratory Disease (HARD) will likely be present.**

Diagnosing Heartworm Disease in Cats

Unfortunately, there is no single benchmark standard used across the veterinary industry for diagnosing heartworm disease in cats. Rather, our veterinarian employs a battery of lab tests in order to determine a cat heartworm diagnosis. These tests may include:

  • A heartworm antibody test determines whether or not a cat's immune system has been exposed to heartworms. This is a very sensitive test and is usually employed first.
  • A heartworm antigen test determines the presence of adult female heartworms. This is more specific than an antibody test, but not as accurate in all cases.
  • Radiographs, or x-rays, that allow us to view the size and shape of a cat's heart. This is helpful because many cats with cat heartworm disease develop enlarged pulmonary arteries or have obstructions in the arteries leading to the lungs.
  • Ultrasounds allow us to view the internal structures of the heart and surrounding vessels in order to assess the condition and function of the heart. However, in some cats with low levels of cat heartworms, this test does not always yield accurate results.
  • A white blood cell count can be measured in cats suspected of having contracted heartworms. Eosinophils are a type of white blood cell which occur in higher numbers when heartworms are present, but can also indicate the presence of other parasites besides cat heartworms.

Heartworm Medicine for Cats

Unfortunately, there is currently no viable heartworm medicine for cats that can fight off an active infestation. Therefore, if your cat is diagnosed with heartworms, we cannot cure it. However, while we cannot defeat existing heartworm disease with medication, this isn't necessarily an indication that they will die soon. While sudden death is possible, it isn't common. If your cat is diagnosed with heartworm disease, 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.

Heartworm Prevention for Cats

The good news for cat owners and their feline friends is that reliable heartworm prevention for cats does already exist. The American Heartworm Society recommends that you "think 12". This means you should give your cat heartworm preventative 12 months a year. Here in LA, because of our mosquito population, we highly recommend all cat owners adhere to this annual preventive medicine protocol.

Have a Veterinarian Check Your Cat for Heartworm Disease at Your Next Appointment

We recommend scheduling an appointment to discuss heartworm prevention for cats with us before your cat contracts heartworms. If you witness any symptoms that might be indicative of cat heartworm disease, please contact us immediately to schedule an appointment. Our veterinary team will provide you and your feline friend with an effective cat heartworm prevention protocol.

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