During veterinary school our professors routinely reminded us that cats are not small dogs, meaning that cats are a unique species that acquire different diseases and respond dissimilarly to the same diseases that dogs acquire. One classic example is heartworm disease. This parasitic disease is carried by mosquitoes. Cats contract this disease after an infected mosquito bites the cat. Immature larvae then travel through the bloodstream, the worms mature, and then can take up residence in the pulmonary arteries, which are blood vessels connected to the heart. Heartworm parasites survive better in the canine bloodstream, and therefore in cats they may migrate to other locations such as body cavities and the brain.
Because cats are not the preferred host for heartworms, it can be more difficult for them to acquire this parasitic infection. One of a cat’s many “superpowers,” amongst landing on his feet from incredible heights and sprinting about 30 MPH, is his relative resistance to heartworm infection. Their unique immune system enables them to fight acquisition of the infection and also has the ability to spontaneously fight infection once acquired. Cats may clear these infections within a span of 2-3 years, versus the more typical 5-7 years in dogs. In light of this information, it seems as though there is nothing to worry about in regards to cats and heartworm disease right? WRONG! Once again, because of a cat’s unique anatomy and other factors, this can be a very serious disease.
Heartworm disease in cats can manifest as a problem once the worm lodges in the pulmonary artery, causing inflammation of the artery and potential heart disease. An additional problem occurs as the worm dies, causing the cat’s immune system to strongly react to abnormal parasite components. This can lead to severe inflammation and potential clots to the heart and lungs. Cats can show a wide range of clinical signs associated with this disease, making it difficult to pinpoint heartworm disease as the underlying cause. Some cats may not show any signs at all, whereas other signs may include cough, difficulty breathing, increased breathing rate, vomiting, decreased appetite, collapse, seizures, and sudden death.
Another dramatic contrast between heartworm disease in dogs and cats is the means by which it is diagnosed. Heartworm disease in dogs is easily detected through a blood test that detects the adult female heartworm. This test can be used in cats; however, because a cat may harbor between 1-6 worms, there is a much higher chance that the worm(s) present will be male or too immature to detect. This presents as a false negative test. Additional blood testing can be done to determine if the cat’s immune system has been exposed to the disease, but this test does not show whether or not the cat has an active infection or may have been exposed years ago. Additional diagnostics may be performed to help confirm heartworm disease including chest x-rays to observe heart or lung changes and echocardiograms (heart ultrasound) to look for the worm.
If a cat has been diagnosed with heartworm disease, treatment unfortunately may not be an option. Dogs are commonly treated with several oral and injectable medications to kill the heartworms. Cats, in contrast, cannot be treated with the medication used to kill canine heartworm as cats react adversely to the medication and can die from sudden death of the heartworm themselves. Supportive care may be administered to help manage symptoms, but is typically not a curative treatment. In rare instances, surgery can be performed to remove the worm from the vessels near the heart.
Because heartworm disease in cats can cause severe disease, is difficult to diagnose, and almost impossible to treat, the best plan of action is to prevent the disease. There are many prescription products available that are used to prevent heartworm disease. These products are monthly medications that often are administered either orally or topically. Many heartworm preventatives often have the added benefit of preventing other parasitic disease such as fleas, ear mites, and intestinal parasites. It is recommended that cats receive heartworm prevention yearly, including indoor only cats as mosquitoes can still enter enclosed buildings. Please contact us today for further information regarding heartworm disease and prevention. Additional information may also be found through the American Heartworm Society website at http://www.heartwormsociety.org/