The American Heartworm Society released updated guidelines in June to help veterinarians better manage—from prevention to diagnosis—heartworm disease in dogs and cats. The revisions are based on recent research from pharmaceutical companies, private laboratories and veterinarians, and parasitologists from several universities. Primarily, three guidelines were updated during this year's revision.

First, the AHS recommended testing cats and dogs annually for heartworm disease. In 2002, the Food and Drug Administration reported to the AHS that it had received claims of lack of efficacy among heartworm prevention products, said Dr. Tom Nelson, AHS president. In response, the AHS updated its guidelines in 2003 and recommended annual testing in certain U.S. regions. During the past few years, however, the society has found that some clients are still not adequately administering prevention products. In addition, Dr. Nelson suggested that heartworms could be developing a resistance to the products.

"The society believes compliance is a bigger issue than the resistance issue, but the only way we'll know is to have more frequent testing," Dr. Nelson said.

During its revision, the AHS also recommended additional heartworm testing when switching prevention products. Dogs and cats should be tested for heartworm disease before switching and then four months after switching. By testing four months afterward, as opposed to the six months originally recommended, veterinarians will be able to better determine whether the old or new product led to an animal contracting the disease. The society recommended an annual test a year from the date of the four-month test.

The third updated guideline states the society's support of year-round heartworm disease prevention. Many prevention products have a reachback, or an extended period of effectiveness, of six to eight weeks, Dr. Nelson said. If a client forgets to administer the product to the animal, or if the animal doesn't ingest it, the animal will be protected during the skipped month.

To access the 2005 Guidelines for the Diagnosis, Prevention, and Management of Heartworm Infection in Dogs and the 2005 Guidelines for the Diagnosis, Prevention, and Management of Heartworm Infection in Cats, visit www.heartwormsociety.org and click on "2005 AHS Treatment Guidelines."