Heartworm Disease in Cats

What is Heartworm Disease in Cats and How Can It Be Prevented?

Dirofilaria immitis is a parasite that causes heartworm disease. It is transmitted by mosquitos. Although cats can be affected by heartworm, they are able to resist it and are a good host. Heartworm is less common in cats than it is in dogs. Cats are only affected by 5-20% of heartworm.

Cats only 25% of heartworms become adults. Cats have a lower worm burden, usually one to four worms per cat. Also, less than 20% of microfilaria (infective) form of heartworm will be produced. Aberrant heartworm migration is a condition in which heartworms do not migrate to the pulmonary vessels and instead travel to other parts of the body or the central nervous system. Cats have higher rates.

Heartworms’ life cycle is complicated and includes many stages, either larval or immature.

  1. A mosquito can contract microfilaria by biting a heartworm-infected dog.
  2. After being ingested, microfilaria will transform into L1, L2 and L3 larvae over the next 10-14 day.
  3. The L3 larva is now able to infect other dogs and cats after the third molt.
  4. A mosquito bites a cat, and then transfers infective L3 via saliva to the bite wound.
  5. The L3 remains in the cat’s tissues for 3-4 more days before it molts to L4.
  6. L4 is kept in the tissues for approximately two months.
  7. L4 finally molts into L5, an immature adult. The tissues are then removed via the bloodstream.
  8. L5 is found in the pulmonary arterial, which are the vessels that carry oxygen-poor blood from heart to the lungs.
  9. L5 continues to grow in the pulmonary vein for another 4-6 month before it finally becomes an adult heartworm. Some worms can release microfilaria into their bloodstream to restart the cycle.

The American Heartworm Society splits heartworm disease in cats into 2 stages.

  • Stage 1 is when L5 larvae enter the pulmonary arteries. Many of them die. As the parasites attack the vessels and hearts, this causes an acute, severe inflammatory reaction. Researchers and veterinarians call this acute inflammatory response heartworm-associated respiratory disorder (HARD). The immune system is actively suppressed by the adult worms as the living worms age, so the inflammatory response decreases.
  • Stage 2 is when adult heartworms are killed, triggering an allergic, often fatal, response. Because cats have small blood vessels, the dead worms trigger a strong pulmonary inflammation cascade. An embolism can easily occur when an adult heartworm is killed. Cats who survive adult heartworm death inflict permanent lung damage on top of chronic respiratory disease.

Heartworm Disease in Cats: Signs and symptoms

The severity of heartworm disease can vary widely in clinical signs. Some cats may not show any signs. The most common symptoms are caused by the adult heartworm suddenly dying, causing acute problems within the cat, or abnormal worm migration that causes tissue damage. Veterinary specialists often see the following signs in cats that show signs of illness:

  • Lethargy
  • Coughing
  • A decreased appetite
  • Weight loss
  • Tolerance is a virtue
  • Vomiting
  • Difficulty in breathing
  • Increased respiration
  • Breathing open-mouth
  • Neurologic disorders
  • Heart murmur
  • Sudden death

Heartworm Disease in Cats: Causes

Heartworm disease is caused by the parasite Dirofilaria Immitis. It is transmitted via mosquitoes. Heartworm is more common in warm areas, such as the south of the United States. Although outdoor cats are more likely to contract heartworm, indoor cats can also be infected if the mosquito enters their home.

How veterinarians diagnose heartworm disease in cats

It is more difficult to diagnose heartworm disease in cats than it is in dogs.

  • Microfilaria tests may show frequent false negatives because cats have very few microfilaria.
  • Antibody blood test can detect immature infection early, up to 2 months after the initial infection. A positive test does not necessarily mean that the adult infection has been confirmed. It can also remain positive even after the cats have been removed.
  • Antigen Blood Test is the gold standard for diagnosing heartworm disease in dogs. However, it can only detect the presence of females. Cats can have low or single-sex (i.e. This method of testing can also miss feline infections that are not caused by worms.
  • Cat heartworm disease may be diagnosed by x-rays or chest radiographs. In about half of cases, x-rays can show common features of heartworms. The following are some of the common features:
    • Large vessels
    • Inflammation of the lungs
    • Lung edema
  • Ultrasound of your heart can be used to visualize live worms inside the pulmonary vein and right side. It can be used to determine if there are any abnormal pulmonary pressures, and also exclude or confirm cardiac disease.

Heartworm infections can be suspected by positive tests, radiographs showing enlarged arteries, and heart changes. Your vet will perform a physical exam and other tests to determine the severity level of your cat’s heartworm disease.

Heartworm Disease Treatment in Cats

Heartworm disease is a difficult condition to treat in cats. Cats can be poisoned by many common treatments, including melarsomine, the most popular canine treatment. American Heartworm Society is the most respected expert in heartworm care for pets. They do not recommend that you use therapies to kill adult heartworms in cats.

Cats that are not showing any clinical signs may be able to be monitored over time for spontaneous healing. The cat’s immune system naturally heals the heartworm infection. This is not a treatment. Ivermectin can be used to reduce the number of worms in cats if it is given for a prolonged period (2 years). Both ivermectin and spontaneous-cure cats can cause allergic shock or inflammatory reactions.

To decrease the cat’s strong inflammatory response, veterinarians might prescribe steroids such as prednisolone. Supportive care is required for cats suffering from acute respiratory distress or shock. Your veterinarian may prescribe the antibiotic doxycycline for Wolbachia bacteria. This bacteria lives in heartworms and can cause inflammation. To relieve respiratory distress, bronchodilators such as theophylline or terbutaline may be recommended.

Heartworm disease is a difficult condition to manage in cats. Therefore, surgery is the best treatment.

The more invasive procedure can be used to remove heartworms by entering the chest cavity and using forceps. All forms of heartworm surgery in cats can cause circulatory collapse and even death.

Acute respiratory distress in cats should be treated immediately with intravenous fluids, oxygen therapy, intravenous steroids, and bronchodilators. If a cat is experiencing respiratory distress such as open-mouth breathing, it is important to immediately seek emergency veterinary treatment.

Prevention of Heartworm Disease in Cats

Heartworm can be a frightening but preventable condition. There are many monthly and bimonthly preventatives for cats. Many prevent heartworm in cats.

Kittens can begin preventatives at 8 weeks old and continue them throughout their lives. It doesn’t matter how much time cats spend indoors; mosquitos can easily enter. The following are common heartworm prevention drugs:

  • Heartgard
  • Moxidectin
  • Milbemycin
  • Selamectin

Heartworm Disease Treatment for Cats

To monitor heartworm status in heartworm-positive cats, they should have their serologic testing, echocardiograms and chest radiographs done every six to twelve months. To gather the most information, vets should perform both antigen and antibody tests.

After blood tests have been negative and all radiological and clinical signs are resolved, veterinarians will cautiously declare that a cat has recovered from heartworm disease. Heartworm disease has a median survival rate of four years for cats.

Heartworm-positive cats must be managed with care. This requires close monitoring, extensive discussions with vets, and a thorough understanding of the heartworm risks in cats. The American Heartworm Society has many great articles and additional information about feline heartworm disease.

FAQs about Heartworm Disease in Cats

What is the maximum lifespan of a cat with heartworm disease?

At the time of diagnosis, the median survival time for cats is four years.

What are the signs and symptoms of heartworm disease in cats.

Asymptomatic cats may not be present at all. However, the most common signs of asymptomatic cats include lethargy and coughing.

Is it possible to cure heartworm disease in cats?

Yes, but it can be dangerous and take quite a while.

Are there any over-the-counter heartworm preventatives for cats?

Only a prescription from a veterinarian is required to use heartworm preventatives.

Is heartworm disease fatal in cats?

Cats can contract heartworm, which can cause death and make it difficult to predict what will happen.

Is heartworm disease contagious in cats?

Without an intermediate vector such as a mosquito, heartworm cannot be transmitted from one cat to the next.

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