This week's case is about a one and a half year old blue point Siamese. Romeo moved from New Jersey to Arizona at the beginning of 2011. His owner brought him into the clinic because he had been coughing for a few months. His previous veterinarian had done x-rays and saw that he had bronchitis - inflammation of the airways - but was not able to determine the cause. His owner told me that Romeo was mainly an indoor cat, but he did sit outside in a large cage for a while some days. Hearing that the cat had some outdoor contact, my first thought was to rule out heartworm disease.
Heartworms are injected into a cat by a mosquito. The heartworm larva will then travel throughout the blood stream and pass through two more larval stages before becoming a worm. We obtained a blood sample from Romeo and ran an antibody and antigen heartworm test. The antibody test would show if he had any exposure to heartworms sometime in the last months or years. The antigen test detects if there is an adult female worm in the cat's body. Cats are actually good at fighting off the heartworm infection and will only have immature worms or one or two adult worms if any survive. Dogs, on the other hand, tend to have many worms in the heart and lungs.
This ability to resist the parasite makes it difficult to definitively diagnose heartworm disease in cats since many infected cats have no worms that will cause the antigen test to turn positive. The cat may also completely fight off the parasite and have his antibody test turn negative after months or years. But even if a cat has beaten the parasite, his lungs may still have lasting damage from the heartworm. While fighting off the parasite, the immune system will mount an inflammatory response that leads to significant lung disease. This is called Heartworm Associated Respiratory Disease (H.A.R.D.). The disease can be mild to severe and can cause various symptoms including coughing, difficulty breathing, vomiting, weight loss and lethargy.
Romeo's antigen test was negative but his antibody test was positive. This did not tell us if he had any heartworms currently in his system but it did tell us that he was exposed at some point. I prescribed steroids for Romeo to help reduce the inflammation in his lungs. This decreased the irritation and mucus secretions so that he would not cough. I hoped it would also prevent further damage to his airways. He immediately improved and is no longer coughing. He is back to himself, and his owner is protecting him from being infected with heartworm again with the regular use of Revolution, a monthly heartworm preventative.
We still do not know how much damage has been done to Romeo's lungs and if he will need to be on steroids for the rest of his life or not. He likely was exposed to the heartworms back in New Jersey before he moved here. However, heartworm disease is becoming more prevalent in Arizona and can be spread by mosquitoes here just as easily as anywhere in the country. We strongly encourage heartworm preventative for all cats living in the valley.
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Dr. Judy Karnia
