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Many people are still not aware that cats can get heartworms. In fact, less than 5 percent of cat owners use a heartworm preventive on their pets compared with 50 percent of dog owners. Do we love our dogs more than our cats? I don’t believe we do. I think cat owners just need to learn about the risk these parasites pose to their pets, and so I’d like to share my top five myths about feline heartworm disease:
Cats are getting heartworm far more often than previously thought. I was a skeptic about the frequency of feline heartworm infection, so I conducted a yearlong study examining shelter cats in the Gulf Coast area. The results certainly got my attention. I found that 26 percent of the cats had been infected with heartworm larvae at some point in their lives, and I found adult heartworms in 10 percent of the cats. Compare this to the feline leukemia (FeLV) infection rate of 5 percent and feline immunodeficiency virus (FIV) rate of 6 percent, and you can see that feline heartworm is much more widespread.
Indoor cats are not impervious to heartworm. A study conducted by North Carolina State University found that 27 percent of the cats diagnosed with heartworm were inside-only cats. It takes only one mosquito to infect a cat, and because mosquitoes can get indoors, both indoor and outdoor cats are at risk and should receive heartworm preventive medication.
The name “heartworm disease” is a misnomer for cats, as the worm mostly affects the lungs and not the heart. The most common signs of feline heartworm disease are coughing, vomiting and difficulty breathing, but can also include: anorexia, blindness, collapse, convulsions, diarrhea, fainting, lethargy, rapid heart rate, weight loss and sudden death.
The signs of feline heartworm disease are often mistaken for feline asthma, allergic bronchitis or other respiratory diseases, so cats with heartworm disease may be misdiagnosed. A cat may even exhibit no signs at all and die suddenly. Because cats are unique in how their respiratory systems react to heartworms, a new name has been given to this set of symptoms: Heartworm Associated Respiratory Disease, or HARD. Cats that suffer from HARD can have difficulty breathing and can die from the disease. There is no effective way to cure the disease once an infection occurs.
With dogs, heartworm typically isn’t a problem until the worms reach the adult stage and lodge in the pulmonary arteries and heart. Cats, however, do not need an adult heartworm to show signs of the disease; in fact, larvae are a main cause of the problems. Studies show 50 percent of cats infected with heartworm larvae have significant damage to the small arteries supplying blood to the lungs.
Diagnosis is much more difficult for cats than it is for dogs, and tests are not the final word on infections. The tests most commonly used in dogs only detect adult female worms. Since most cat infections do not make it to the adult stage, and those that do may only have male worms, many infections are missed by current testing practices. If your cat is showing signs of heartworm disease, talk to your veterinarian. Treatment of heartworm is often ineffective or problematic in cats. That's why prevention is the very best strategy for controlling the disease.
For more information, visit www.knowheartworms.org, www.heartwormsociety.org or www.petsandparasites.org.
Dr. Tom Nelson graduated from Texas A&M University and is the previous past president of the American Heartworm Society. He is currently on the board of the Companion Animal Parasite Council and sits on the International Feline Heartworm Council. Dr. Nelson is the surgical director of the Animal Medical Centers of Northeast Alabama in Anniston, and is a frequent contributor to veterinary medical journals and textbooks on the topic of heartworm disease. He is the lead author of the recently released Heartworm Society Guidelines.
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