Guidelines for heartworm infection in cats updated, new syndrome defined

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The American Heartworm Society released the 2007 Guidelines for the Diagnosis, Prevention and Management of Heartworm Infection in Cats. The most notable update was the inclusion of information on the newly defined heartworm-associated respiratory disease.

According to the AHS, some cats never develop clinical signs of heartworm infection, but even a small number of worms can be life-threatening. When signs are evident, they usually develop either in the first stage when the heartworms enter a blood vessel and are carried to the pulmonary arteries, or in the second stage when the adult heartworms die. The AHS reported that the signs associated with the first stage are often misdiagnosed as asthma or allergic bronchitis when, in fact, they are actually a result of HARD. The second stage often leads to fatal acute lung injury.

Another highlight of the updated guidelines is information on interpreting serology test results. According to the AHS, heartworm infection is harder to diagnose in cats than in dogs, and it is easy to overlook. Diagnostic tests have limitations, so test results negative for heartworms do not necessarily rule out an infection. Antigen tests, for example, detect only adult female or dying male worms. Immature or male-only worm infections are rarely detected.

To help spread the word about the updated guidelines, the AHS will embark on a public awareness campaign called KNOW Heartworms in partnership with the American Association of Feline Practitioners and underwritten by a grant from Pfizer Animal Health. Information on the campaign is available at

Research for the guidelines is conducted by several sources, including pharmaceutical companies, private laboratories, private-practice veterinarians, and parasitologists at several universities. The AHS then compiles all the findings to create the guidelines, which are updated on an ongoing basis. To view the guidelines, log on to