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Preventing And Treating Heartworms In Cats


At Countryside Veterinary Clinic, our highly experienced team of veterinarians and veterinary support staff have been helping educate our clients about feline heartworms.

What Is Dirofilariasis, AKA Cat Heartworm?

Dirofilaria immitis is a blood-borne parasitic referred to as cat heartworm. Heartworms in cats are spread through mosquitos that carry cat heartworm larvae. The severity of heartworms 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 are less prevalent in felines than in canines, feline heartworms are still a dangerous disease that has been on the rise in America. The risk of heartworm disease is about equal for both indoor and outdoor cats.

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 the disease. However, this doesn't necessarily mean that cat heartworm disease isn't present.

The most common clinical signs include:

  • Difficult or labored breathing
  • Coughing
  • Sudden death

On occasion, an apparently healthy cat 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 long before serious medical issues or life-threatening emergencies develop by simply implementing preventive measures.

How Are Cat Heartworms Transmitted?

Upwards of thirty species of mosquitoes can act as cat heartworm transmitters. 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 its mouth.

When an infected mosquito bites a cat, it injects the heartworm larvae into the cat. 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. Once this occurs, they mature into adult cat heartworms and can reproduce about six months from the time of the invasion. Approximately eight months after the invasion, cat heartworm begins to produce a new crop of microfilariae, which 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, which can become fatal.

Diagnosing Heartworm For Cats

Unfortunately, there is no benchmark standard that is used across the veterinary industry for diagnosing heartworm for cats. Rather, our veterinarians employ a battery of lab tests to determine a cat heartworm diagnosis. These tests 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 it is usually employed first.
  • A heartworm antigen test determines the presence of adult female heartworms. This is more specific than an antibody test, but it is not as accurate in all cases.
  • Radiographs, or X-Rays, allow us to view the size and shape of a cat's heart. This is helpful because many cats with cat heartworms 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, to assess the condition and function of the cat's 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 that occur in higher numbers when heartworm for cats is present, but they can also indicate the presence of other parasites besides cat heartworm.

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 heartworm, we cannot cure it. However, while we cannot defeat existing heartworm disease with medication, this isn't necessarily an indication that your cat will die soon. While sudden death is possible, it isn't common. If your cat is diagnosed with heartworm, he or she 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 your cat 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 exist. Veterinarians strongly recommend that all cats receive monthly heartworm preventive medications in areas where mosquitoes are active all year round. Here in Maryland, because of our mosquito population, we highly recommend all cat owners adhere to this annual preventive medicine protocol.

Discuss Heartworn Disease In Cats With Your Veterinarian At Your Next Appointment

We recommend scheduling an appointment to discuss heartworm prevention 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. 

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