Feline Heartworm Disease:                    

     Heartworms are actual worms that infest the heart of dogs, cats and ferrets.  These parasites are 3-6 inches long and live in the right ventricle of the heart and the pulmonary artery.  Heartworms are a very common problem in this area.  The routine use of heartworm preventatives has helped to reduce the incidence of this disease among our patients, but we continue to see infested animals on a regular basis.

     Cats present a real diagnostic and treatment challenge for veterinarians. It has been reported that the incidence of heartworm infestation in cats is 2-20% that of the dog population. The dilemma is that cats may show no symptoms at all or they may show serious symptoms to as few as one worm. Cats may even present as a case of sudden death. Furthermore, routine heartworm tests that we commonly use to diagnose canine heartworm infections are commonly unable to sensitively diagnose this disease in cats.

Because this area is endemic for heartworm infection we believe that clients should be encouraged to provide protection to their cats as well as their dogs. 

     Heartworms are transmitted by the mosquito.  The mosquito is an absolute necessity for transmission to occur.  Direct contact with an infested animal will not transmit the disease.  Once the microfilaria is released into the bloodstream by the mosquito, it travels through the bloodstream and body while molting into more advanced stages for several months before ultimately landing in the heart as an adult.

      All heartworm preventatives act to kill microfilaria only—not adult heartworms.  Therefore, we strive to educate owners of new puppies and kittens about heartworms and start a preventative medication early.

Treatment of heartworms is not possible in cats. Killing of the adult heartworm in a cat will result in the cat’s death.
     Cats with clinical signs consistent with heartworm disease (vomiting, coughing, or wheezing) are often tested for heartworm disease. These tests may include a CBC, difil test, Antigen test, Antibody test, radiographs and/or echocardiography. 
     Cats are truly a diagnostic dilemma when it comes to diagnosing heartworm disease. Some cats that have positive antibodies are not infested and some heartworm infested cats have a negative antibody test. Diagnosing heartworm disease in cats requires a suspicion of disease and an astute veterinarian. Often it is necessary to draw conclusions from indirect results of tests.

     It is extremely important to realize that 30% of heartworm infected cats are 100% indoor cats.

     Due to the severity of heartworm infestation in cats, the difficulty in diagnosing, and the high prevalence of heartworm disease in the area, we recommend that all cats be on a monthly heartworm prevention.
      It is not required to test cats annually for heartworm disease or to test them prior to starting prevention medication. This is due to the low sensitivity of these tests and the difficulty in interpreting results. Furthermore there is little risk that a cat will react adversely to starting heartworm prevention, even if currently infected. Cats are generally tested when there are symptoms consistent with disease. Depending on individual circumstances, the doctors may at times recommend routine testing based on their professional judgment.