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Many dog owners know the importance of giving their canine companions heartworm prevention, but relatively few cat owners follow suit. It is a common misconception that cats, especially those that live outdoors, are not at risk for heartworm disease. However, heartworms have been detected in cats in all 50 states.
In a study done in North Carolina, 28% of the heartworm positive cats were indoor only. It is the mosquito that serves to spread the disease from an infected host, and these tiny insects can easily get indoors. The infected mosquito bites a cat, injecting the heartworm larvae into the skin. From there, the larvae migrate through the muscle to the blood vessels and organs, particularly the lungs. The cat’s immune system reacts to these invaders and may be able to keep the larvae from developing into adults. Even if successful, this immune response in and of itself can result in inflammation of the lung tissue, airways and associated blood vessels. Additionally, even the immature larvae can cause physical blockage of smaller vessels, resulting in damage and dysfunction.
Consequently, any signs of heartworm disease that are noticeable in cats tend to be respiratory in nature, thus the term Heartworm Associated Respiratory Disease (HARD). Fragments of dying worms can also cause blockage of vessels in any area of the body. Aberrant migration of worms to the brain, eye, or spinal cord may manifest in neurological signs.
Symptoms Associated with HARD include the following:
Due to the immune response of the cat, there may be only one or two larvae that manage to develop into adult worms. This makes it difficult to detect their presence, as commonly available tests work by identifying heartworm antigens in the blood sample. These antigens are proteins produced by the adult female worms. A cat could potentially host multiple adult male worms and would still test negative for heartworms.
There are also antibody tests available, which would detect exposure to heartworms, but they do not determine if there are heartworms currently present in the cat. For instance, a cat that was infected but whose immune system was able to prevent all the larvae from developing would have antibodies present, but no active infection.
Not only are heartworms in a cat difficult to detect, there is currently no treatment available. The drug that is used to treat heartworms in dogs can be fatal to cats. This makes prevention essential to our feline friends’ health.