Heartworm Dangers

Find out how to protect your cat from this rare, but deadly disease.

By Arnold Plotnick, DVM

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Difficult Diagnosis
Feline heartworm disease is difficult to diagnose. One method is to look for microfilaria ("baby" heartworms) circulating in the bloodstream. However, the cats intense immune response quickly eliminates the microfilariae from the bloodstream making the method ineffective. Finding these microfilariae indicates the cat is infected. A negative test is inconclusive.

When the worms reach maturity (about 6 months of age), they shed proteins called antigens into the bloodstream. The cats immune system makes antibodies against the antigens. One method of diagnosis is to look for antigens, antibodies or both in the bloodstream. Antigen tests actually detect proteins shed by the adult female heartworms in the cats blood. Antibody tests detect the presence of antibodies that the cat made in response to heartworm exposure. Each test gives important information, but both have limitations. The decision of which test to use first depends on the veterinarians preference. Some veterinarians prefer to antibody test all cats initially, with a negative test generally eliminating the need for further testing. A positive test indicates exposure and will require additional testing to see if there are adult worms in the heart. Because of the limitations of both tests, many veterinarians perform both tests routinely. Additional tests that may be useful include chest X-rays and cardiac ultrasounds.

Tried Treatments
Treatment options for FHD are limited. Most veterinary cardiologists do not advocate using drugs to kill the adult worms in cats. Instead, cats are treated symptomatically, with short-term use of anti-inflammatory drugs to reduce the intense allergic reaction that develops.

"I treat with the anti-inflammatory drug prednisone," Norsworthy says.

Aspirin is often recommended to reduce the risk of blood clots in the lungs. There is no proven benefit, but giving aspirin is generally harmless and inexpensive.

Prevention remains the best method of dealing with FHD. The disease is entirely and easily preventable. Three FDA-approved drugs are available for monthly use in cats. Ivermectin as a chewable treat, milbemycin as a flavored tablet and selamectin as a topical formulation. Because the consequences of FHD are potentially dire and treatment options are limited, monthly preventatives should be given to cats living in endemic areas. Your veterinarian can help advise you as to the best prevention program for your cat.

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Reader Comments

janet    bethlehem, PA

7/23/2010 4:50:43 AM

good article thanks

Carole    Glendale, AZ

4/22/2008 8:09:37 AM

The artle was very interesting,especially where they say aspirin is cheap (true)and will not do any harm. I take issue with that statement, although I am not a vet, I have been given to understand that a cat can only metabolize a small dose of aspirin every 2 or three days; snall dose being comparable to half baby aspirin or half of an 81 strength aspirin, and I would check with my vet about any dosage of aspirin before I gave it to my cats

Lena    Lula, GA

4/12/2008 7:30:34 AM

I have a cat that was antibody (+), antigen(-). It is confusing(and I have been a vet tech for 26 years)in that neither test is conclusive as an antigen (-) cat could have male worms that do not cause the antigens to be produced. The vets I work for said the key to survival is for the worms to die slowly. They said to continue his heartworm preventive (interceptor). But a drug rep said it is can be harmful to give a (+) animal heartworm preventive. He has been on it for 9 months now and was on heartguard before. I wish there was more info on treatment.

Sara    Atlanta, GA

10/18/2007 4:18:35 AM

This is why I give my cats heartworm medicine even though they are indoor cats. It's better to be safe than sorry.

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