Heartworm Disease in Cats

Dr. Maria Badamo

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Can Cats Get Heartworm Disease? The Answer is YES!

Heartworms are exactly what the name implies, parasitic worms that live in the host (dog or cat) heart. While it is true that dogs are at much higher risk than are cats of getting the typical heartworm infection, feline infection is now known to be a far more widespread problem than previously believed. It can also be much more devastating. If a cat has an adult heartworm infection is more common for the infection to consist of only one or two worms at most. However, even though the number of worms is fewer, they commonly have more serious symptoms than what we commonly see in dogs. For example, it is not uncommon for a cat that has adult heartworms to suffer an acute sudden death. While cats can get an adult heartworm infection, what is more likely to happen in our feline friends is something called H.A.R.D – Heartworm Associated Respiratory Disease

What is H-A-R-D (Heartworm Associated Respiratory Disease)?

To understand what HARD is in the cat we must first consider the life cycle of the heartworm. The Heartworm life cycle starts out in the blood stream of a host and is called microfilaria. The microfilaria are basically baby worms that are produced by the adult female worms. They circulate through the infected host blood stream until the host is bitten by a mosquito. Once the mosquito bites, the blood from the host containing the microfilaria enters into the mosquito. In the mosquito the microfilaria develop into infective L3 stage larvae. It is these Larvae that infect a new host when this mosquito bites a new animal. When the L3 larvae infect a host they then migrate through the body over the course of 6 months making their way to the heart.  During this time they are continuing their development from L3 Larvae to L4 Larvae, then Juvenile stage. In order to reach the heart the worms must migrate through the lungs. The cat is not the intended host, so when migrating though the lungs the worms will encounter the feline immune response which is especially more reactive to the heartworm larvae than the dogs immune system. It is the cat’s immune response to the larvae that will cause Lung lesions that develop while targeting the migrating worms. These lesions, in large enough numbers, can cause significant damage to the lungs causing secondary respiratory disease.

The signs of HARD can be similar to symptoms seen in feline asthma patients including coughing, and respiratory distress. Because of this Feline Heartworm associated Respiratory disease is often misdiagnosed as feline asthma. Testing for feline heartworm disease can be tricky and many cats that have been exposed and have lung lesions may not test positive for heartworms. Making things even more difficult the medication used to treat heartworm infections in dogs cannot be used in cats, so prevention is the only means of protecting cats from the effects of heartworm disease. Since Mosquitoes often venture indoors we recommend all cats both indoor and outdoor dwelling cats be protected on monthly Heartworm prevention year round.

For more information on Feline Heartworm disease visit the American Heartworm Society website: https://www.heartwormsociety.org/