Heartworms are a major concern for dogs and most informed pet owners are fairly well aware of the risk. However, many do not realize that cats also are susceptible to heartworms and heartworm disease.

Heartworms in cats, however, behave much differently than heartworms in dogs.

Heartworms - Similarities and Differences Between Cats and Dogs

Heartworms are spread to cats just as they are to dogs, through the bite of a mosquito.

However, after becoming infected, heartworms tend to act a bit differently in the feline body than they do in the canine body.

Unlike dogs, cats are not natural hosts for heartworms. The body of a heartworm-infected cats generally mounts a very strong immune response to the heartworms. Very rarely do cats end up with large numbers of adult heartworms living in their hearts. Generally, the worms that are able to mature and migrate to the heart are much smaller than those found in infected dogs. Often, infected cats have only one or two relatively short adult heartworms living inside of their heart.

However, in cats, the majority of the damage done by a heartworm infection is the result of the immune response mounted by the cat's body. Most of the damage occurs in the lungs, first when the heartworm larva migrate through the rest of the body to the lungs and then later when the heartworms die in the lungs. This respiratory damage has come to known as heartworm-associated respiratory disease, or HARD.

Symptoms of Feline Heartworm Disease

The symptoms most often seen in cats with heartworm disease are respiratory in nature. This differs from the dog, where heart failure is a common complication of heartworm disease.

Symptoms expected in cats with heartworm disease include:

• coughing
• vomiting
• respiratory difficulty
• lack of appetite
• depression

Sudden death can occur in cats with heartworm disease and can happen without any previous signs of illness.

Heartworm disease in cats appears very similar to feline asthma and is often misdiagnosed as asthma.

Diagnosing Heartworm Disease in Cats

The diagnosis of heartworm disease in cats is much less straight forward than diagnosing it in dogs as well. Generally a blood test is all that is needed to determine whether a dog is infected with heartworms or not. However, in a cat, this is not the case. Currently available tests for heartworms in cats are much less accurate than in dogs.

In cats, the microfilaria are usually destroyed shortly after infection so tests that look for microfilaria are usually useless in cats. Both a heartworm antigen and heartworm antibody test are recommended for cats that are suspected of having heartworm disease. However, it is not impossible for both of these tests to be negative even in a cat that is infected with heartworms.

Radiographs of the chest and echocardiography are also used to examine cats for heartworm disease and can sometimes be helpful in the diagnosis.

Treatment of Cats with Heartworm Disease

There is no medication that can safely kill the adult heartworms living in the heart of an infected cat. The medication used to treat dogs for heartworms, Immiticide®, is not safe for use in cats.

The mainstay of treatment for cats with heartworm are corticosteroid products, such as prednisolone. These products are used because of their anti-inflammatory effects and act to reduce the inflammation resulting from the immune response mounted by the cat's body within the lungs.

Other treatments are similar to those used in feline asthma and may include bronchodilators such as albuterol, terbutaline or theophylline. These drugs act to open up the airway passages and help make the cat breath easier.

Heartworms can and do infect cats but heartworm infection in cats is much different than heartworm disease in dogs. Fortunately, there are several products that are quite effective in preventing heartworm infection in cats. These products include Advantage Multi for Cats®, Revolution® and Heartgard for Cats®.

Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.