Heartworm in Cats PDF Print E-mail

Overview

Heartworm in Cats: Overview

Heartworm has become a very real problem for both indoor and outdoor cats. Though generally thought of as a dog disease, cats are one of over thirty species of animals that can be adversly affected by heartworms. In certain areas of the country it's believed that up to 15% of indoor cats have been exposed to heartworm disease. The rate of outdoor cats infected is much higher.

A cat's immune system is much better at fighting off heartworms than a dog's, but serious problems are an all too often result of infection.

Heartworm in cats generally manifests itself more as a respiratory illness than as cardiac disease, and symptoms can often evade the owner's notice. It is a very serious disease, though, and can lead to sudden death from respiratory failure.

Symptoms and Diagnosis

What are the symtoms to look for?

The heartworm itself has evolved to survive best by reaching the heart in canines, so it can be very difficult to notice any obvious symptoms in cats.

The most common signs are:

  • Sudden onset of coughing and rapid breathing
  • Weight loss
  • Vomiting
  • Sudden overwhelming respiratory failure

These clinical signs can be caused by several other diseases. If your cat shows these symptoms it is best to have your vet examine the cat.

How are heartworms diagnosed?

There are several methods used in diagnosing heartworms; unfortunately, none are 100% reliable so a combination of tests is often needed. The diagnostic sequence usually progresses as follows:

Blood Tests

There are two blood tests that can be used to diagnose heartworms.

  1. Heartworm Antibody Test
    • Shows if the cat's immune system has been exposed to heartworms.
    • Positive test shows either an active infection, or that the cat has been exposed in the past
    • Very sensitive and accurate
    • Positive result leads to more testing
  2. Heartworm Antigen Test
    • Detects the presence of at lease two adult female heartworms
    • Positive test indicates that heartworms are present
    • Negative test does not mean that they are absent, as all worms may be male

A diagnosis of heartworm infection is confirmed when both the antibody and antigen tests are positive. This information, combined with medical history and clinical signs, are most commonly used to diagnose feline heartworm disease.

X-Rays

X-rays are used to determine the size and shape of the cat's heart, and to measure the diameter of the pulmonary arteries. Often the heartworms will never make it to the cat's heart, but will instead lodge themselves in the pulmonary arteries. X-rays are only effective in later stages of disease.

Ultrasound or Echocardiography

An ultrasound machine produces an image of internal organs and structures without the use of radiation. It is a testing procedure that is becoming more and more common in veterinary practices. With it, one is able to view the internal structures of the heart and the pulmonary arteries. In some cats, the actual heartworms can be seen; this finding confirms the presence of heartworms. However, in many cats the worms are not seen since there are generally only one or two worms present.

Treatment

Can feline heartworm disease be treated?

There is no drug approved for treating heartworms in cats. One of the drugs for treating dogs has been used in cats, but there are potentially significant side-effects. Another problem is that when the heartworms die they pass through the pulmonary arteries to the lungs. This can result in sudden death.

This presents a real dilemna for the owner, and vet, when a diagnosis of heartworms is made. One of two choices must be made:

  1. Treat with the drug designed for dogs. However, this is a drug that has been shown to have side-effects in cats. These side-effects include acute pulmonary (lung) failure and death in a small percentage of cats.
  2. Treat the symptoms of heartworm disease and hope the cat outlives the worms. Since heartworms live in a cat for about two years, several months of treatment are needed. When cats are in a crisis, they are treated with oxygen and corticosteroids ("cortisone") to relieve the reaction occurring in the pulmonary arteries and lungs, and, if needed, drugs to remove fluid from the lungs (diuretics). When they are stable, they are treated continuously or periodically with corticosteroids. However, the threat of an acute crisis or sudden death always exists.

Home Care

Prevention Is Safe and Easy

Cats given heartworm prevention drugs have not shown signs of toxicity. There is a wide margin of safety, even in kittens as young as six weeks of age.

It is strongly recommended that all cats receive year-round monthly heartworm preventative in areas where mosquitoes are active all year round. Cats that live in colder areas, where mosquitoes are seasonal, should be on monthly preventative for at least 6 months of the year. There are excellent heartworm preventatives now available for cats, making prevention of heartworm disease safe and easy.

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