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Newsletter
Issue 6 Feline Heartworm Disease We are becoming concerned about the presence of feline heartworm disease in our area. During the first three months of 1999 at least six cats evaluated for non specific vomiting and breathing problems have tested positive for heartworm exposure. Out of twenty five tests performed we have identified twelve cats that have been exposed. In other areas of the United States in which heartworm disease is endemic in the dog, more and more cases are being recognized. In certain areas cats are now being placed on the same preventative medication we routinely recommend for the dog in central New York Heartworm disease has been studied for many years in the dog. The signs and symptoms of infection are generally related to right heart failure and related pulmonary (lung and breathing) problems. The adult worms live in the right heart and great blood vessels of the lungs and cause irritation and blood flow turbulence. In addition to the primary problem of blood flow though the lungs and decrease in oxygen to the body, there may be problems related to blood clots. Sudden death may occur due to a stroke like syndrome. The cat has only recently been found to be affected by heartworm disease. Unlike the dog, true heart failure is unusual in the cat. The most common problems are chronic vomiting and respiratory (breathing) problems similar to asthma. In cats with heart failure pulmonary hypertension (high blood pressure in the lungs) is thought to be the cause. Inappetence and unexplained weight loss may also occur. The clinical picture can be vague initially and progress only with time to the more recognizable signs. The disease in the cat is caused by the immature (larval) stages of the worm and exposure rarely leads to the development of adult worms. The natural life cycle of the heartworm involves transmission by the mosquito between dogs. An infected dog or coyote acts as a reservoir of infection, with many larvae circulating in the blood. The mosquito ingests these larvae during a blood meal and they develop into an infective stage over a few days to weeks. The mosquito then can infect another animal by direct inoculation (injection) of these larvae under the skin. These larvae then migrate through the body to eventually live in the right heart of the dog and develop into the adult worms which then produce more offspring. In the cat this complete cycle rarely occurs. In some cases there may be one or more adult worms that develop but this is unusual. The larvae simply migrate and circulate in the cats body and the signs of infections (which may be severe) are related to an immune (allergic) reaction which develops over time. Diagnosis is made by a blood test to identify antibodies against the larvae and adult worms. In most cases only the larval antibody test is positive. If the cat is positive for adult worm antibody then a direct test for protein from the worm (heartworm antigen) is performed. Treatment involves giving the preventative medication over several months to kill the larval worms. Additional medication is given based on the individual problems in each cat. This usually involves treatment for allergic reactions causing vomiting, asthma and hypertension (high blood pressure). The prognosis depends upon the severity and chronicity (length of time) of the disease. Although we are not yet recommending that all cats be placed on preventative it is certainly apparent that a strong recommendation that all dogs (the natural host and reservoir of heartworm disease) be placed on preventative. Our area has been determined to be of moderate risk based on studies over the past several years. The preventative is very effective and considered to be quite safe with few short or long term side effects noted. By keeping the disease suppressed in the dog we are also protecting our cats. |