Understanding Feline Heartworm Associated Respiratory Disease (HARD)

Heartworm disease is not just for the dogs.

 

Heartworm disease has been reported in the US since the 1920’s. Until recently it was believed that cats were only an accidental host and that cats were rarely affected by the parasite. Recent studies show that 25% of cats tested have been exposed to heartworms at some point during their life.  There are now products on the market that can safely protect your cat from heartworm.

Cats are infected with heartworms the same way as dogs are infected, by being bit by a mosquito carrying heartworm larvae. The immature worms lodge in the pulmonary arteries in the lungs. This initial stage of heartworm infection can cause asthma like-inflammation of the lungs. In cats all stages of heartworm larvae and worms have been known to cause disease.

Unlike dogs where may of the larvae survive to become adult warms, in cats only a few grow into adults. It only takes one heartworm to cause severe disease in a cat. The second stage of heartworm infection is associated with worm death. As the adult worms die, it causes more inflammation. Parts of the worms can become lodged in the lung arteries causing severe difficulty breathing shock and sudden death.

Signs of Heartworm Infection

Signs of heartworm infection in cats are often vague and can mimic other diseases. Signs include difficulty breathing, coughing, vomiting, diarrhea, lethargy, weight loss, collapse, and sudden death.

Heartworm disease is carried by mosquitoes. While outdoor cats are at greater risk, 1/3 of heartworm positive cats are indoor only.

Diagnosis of feline heartworm diseases can be difficult. Tests for cats are not always reliable. 

Heartworm antigen tests are not always accurate in cats because cats may be infected with as few as one adult male worm. Since the test detects a part of female worms, this test can produce negative results when a cat is infected.

The heartworm antibody test measure a cat’s immune response to heartworm exposure. Many cats may be exposed to the disease but never become infected. Therefore, the test can be positive when a cat does not have infection. Many times both the antibody and antigen test are performed together to yield more accurate results.

Chest X-rays and Echocardiography can also help to detect changes to the heart and lungs from infection although they cannot be used to solely diagnosis an infection.

There are no safe treatments for feline heartworm disease. Traditional treatments used to kill adult worms in dogs can be very hazardous to cats leading to death. In some instances the worms may be removed surgically but this is a very invasive and risky treatment option. Most heartworm positive cats are supported with medication to control the symptoms of the heartworm disease. Life long support with medications may be necessary to keep cats comfortable and minimize signs of the disease.