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Pet Health Care Articles

Heartworm Disease in Cats
What is Heartworm Disease?

April 16, 2010


Feline heartworm disease develops when a cat is bitten by a mosquito carrying microscopic heartworm larvae (juvenile worms) of a parasite called Dirofilaria immitis. As a mosquito feeds, these larvae are deposited on the pet's skin and quickly migrate into the cat, eventually reaching the cat's bloodstream. Since heartworms typically reside in the pulmonary (lung) arteries and the right side of the heart, infection often leads to severe lung disease and sudden death. In cats, typically only a few worms develop to maturity, unlike dogs where large numbers develop. Unfortunately,
in the cat, even a single heartworm can have fatal consequences.
Recent studies indicate that feline heartworm infection in cats is more common than ever believed. Even indoor cats are at risk of infection because mosquitoes are often found inside homes. Although easy to prevent, heartworm disease continues to be a major health problem in the United States and throughout the temperate and tropical regions of the world. 

Adult female heartworms release their young into the bloodstream of an infected animal, typically a dog or other suitable host. As mosquitoes take a blood meal from these animals, they ingest the microscopic heartworm larvae. Inside the mosquito, the larvae develop into an infective stage within 10 to 14 days. Then, when the mosquito bites another susceptible host, it deposits the infective larvae and the larvae enter the bite wound and begin to migrate. In the cat, it takes six to eight months for heartworm larvae to mature into adult worms. Adult heartworms may live one to two years in cats. 

Symptoms of feline Heartworm Associated Respiratory Disease can mimic many common diseases of cats such as hairballs, asthma, or pneumonia. Symptoms can range from mild and subtle in appearance to severe and life threatening. Signs of disease may include loss of appetite, sluggishness, intermittent vomiting (not associated with eating), coughing, wheezing, and respiratory distress. Since these clinical signs are often associated with heartworm or larval death, signs of HARD can occur when no evidence of infection exists.

Two blood tests are currently available to assist in diagnosing heartworms in cats. Unfortunately, test results do not always produce clear answers. Positive tests indicate heartworms were present, but do not necessarily mean the pet is still infected. Moreover, since tests cannot diagnose very early infection or those infections caused by only one or two worms, negative test results are not always accurate.
Even when heartworm disease is highly suspected, confirming a diagnosis through testing in the cat can be difficult. Multiple blood tests along with chest X-rays and ultrasound imaging of the heart and lungs are often needed to make a diagnosis. 

The best option is the routine use of heartworm preventives.

Unfortunately, no medications exist for the safe treatment of adult heartworms in cats. In some circumstances, surgical removal of heartworms has been successful. However, few surgical specialists are capable of successfully performing this difficult procedure. Since no safe treatment exists for the elimination of heartworms in cats, the best option is the routine use of heartworm preventives to inhibit development of infection. 

Various heartworm preventives are available, including monthly oral and topical formulations. All feline heartworm preventive medications work by killing heartworm larvae acquired during the previous month and do not continue to protect cats from future infection. These products are highly effective, safe, easy to use, relatively inexpensive, and often provide treatment for additional parasites. The best way to eliminate the risk of heartworm infection in your cat is to institute a year-round prevention program.