Campaign leaders want heartworm prevention to become infectious


Orlando - With only 4 percent of cats estimated to be on heartworm medicine, a new campaign from the American Heartworm Society (AHS) aims to change what officials are calling an abysmal prevention rate.

ORLANDO — With only 4 percent of cats estimated to be on heartworm medicine, a new campaign from the American Heartworm Society (AHS) aims to change what officials are calling an abysmal prevention rate.

Topography of infection: Heartworm has been diagnosed in all 50 states. This map outlines endemic regions of the United States.

In fact, AHS, the American Association of Feline Practitioners (AAFP) and Pfizer Animal Health have kicked off a joint educational campaign to increase awareness about heartworm prevention in cats.

Long recognized as a fatal parasitic threat to dogs, heartworm infection is much under-appreciated in cats, says Dr. Tom Nelson, president of the AHS. The reality: 30 feline species are recognized as being susceptible to heartworm and there is a growing body of science on the issue.

"If you see it in dogs, your cats are at risk," Nelson said at the recently concluded North American Veterinary Conference.

Nelson and Dr. James Richards, a feline expert at Cornell University and president of AAFP, are leading a campaign that will include nationwide media contacts, clinic educational kits and a new Web site (

Signs of Heartworm Associated Respiratory Disease

"The dangers are much more significant than we previously believed," Richards adds. "There is compelling evidence that this is a deal, and a whole lot of vets don't recommend heartworm preventive."

Convincing veterinarians of the risk may be the campaign's tallest hurdle.

The evidence

Necropsy surveys of shelter cats, AHS reports, show 50 percent to 70 percent of infected cats have at least one female worm. These shelter-cat studies have shown a distinct correlation to antibodies and occlusive medial hypertrophy of a substantial number of small pulmonary arterioles. These pathologic changes are evident in 79 percent of necropsy-confirmed adult worm infections and 50 percent of adult heartworm-negative-but-antibody-positive cats. The significance of the finding, AHS reports, is that pulmonary disease occurs in those cats that do not develop adult worm infections.

Once skeptical about the risk of heartworm to the feline population, Nelson says to see it is to believe. In the late 1990s, he conducted the first study to examine the frequency of feline heartworm in the Texas Gulf Coast region. After post-mortems on 259 cats, he found heartworm antibodies in 26 percent and adult heartworms in 10 percent of the cases.

He is looking for converts. To find them, AHS plans to take the message to both veterinarians and pet owners in a push to improve compliance with heartworm prevention.

Difficult diagnosis

The campaign's mantra is "Know Heartworms," and it coincides with revised heartworm guidelines for practitioners based on research showing that heartworm larvae at all stages (not just adult worms) can cause serious health problems. Complicating matters, accurate diagnosis can be difficult to achieve, since negative antigen and antibody tests don't automatically rule out the presence of heartworms.

The initial phase of the disease is commonly misdiagnosed as asthma or allergic bronchitis. In reality it's the first sign of a more complex syndrome, Heartworm Associated Respiratory Disease. Clinical signs associated with the acute phase subside as the worms mature, but demonstrable histopathological lesions are evident even in those cats which clear the infection," report AHS' revised guidelines.

"The most notable microscopic lesion is occlusive medial hypertrophy of the small pulmonary arterioles, but other changes also are noted in bronchibroncioles, alveoli and pulmonary arteries."

AHS' message: Heartworm remains a far easier disease to prevent than treat; talk to your clients about the risks.

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