Until recently, most experts would say that cats did not get heartworms.  Over the past few years, research has begun to show that heartworms are much common in cats than was previously thought. 

Prevalence of Heartworm in Cats

There have been laboratory confirmed cases of heartworm in cats in all 50 U.S. states. One researcher who presented at a 1998 heartworm symposium performed random blood tests in cats and found that heartworm disease was more common than feline leukemia (FLV) and FIV or feline AIDS.  Anywhere that dogs are at risk for heartworm, cats are now also considered to be at risk.  

This apparent increase in feline heartworm infection is actually a sign of better detection and understanding of the disease.  Cats may develop only one or two adult worms and, as a result, older heartworm tests that worked on dogs may not be sensitive enough to identify a heartworm infection in a cat. In addition, heartworm disease in cats may be misdiagnosed due to the lack of awareness of the prevalence of the disease as well as the different symptoms that cats develop.

Symptoms of Feline Heartworm Disease

Heartworm in cats often presents differently than in dogs.  Respiratory symptoms, such as coughing and difficulty breathing, are common in cats with heartworm and may be misdiagnosed as asthma.  These symptoms, along with vomiting, weight loss, lethargy, and loss of appetite, may become a chronic disease.  Heartworms can also cause neurological symptoms, seizures, fainting, and death in cats.

Treatment of Heartworm Disease in Cats

Heartworm treatments that work on dogs are dangerous in cats. As many as 70% of cats will die if canine treatments are used.  The best practice for cats with heartworm is to treat the symptoms and allow the adult worms to die a natural death over the course of a couple years. In some cases, the inflammation that occurs when the heartworms die may be life threatening for the cat. 

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Prevention of Heartworm

There are medications available that can prevent heartworm in cats.  If you have a dog and your veterinarian recommends seasonal or year-round heartworm protection, ask about prevention for your cat too.  Heartworm is extremely common in the southeastern U.S. year round and many other parts of the country have a risk of heartworm, especially during warm months.   If your vet is not familiar with the risks of feline heartworm disease, there are guidelines put out by the American Heartworm Society that can help you and your vet make an education decision.

Heartworm and Indoor Cats

It is not just outdoor cats that are at risk of heartworm.  One study found that about 28% of cats that were diagnosed with heartworm were indoor-only cats.  Some researchers theorize that indoor cats may actually be at increased risk since they do not have a built up immunity.  Cats may particularly be at risk if they lie against window or door screens as many indoor cats enjoy doing.  If you live in an area that has a high risk of heartworm disease, consult with your veterinarian about the need to treat your indoor-only cats. 

Heartworm disease in cats is still not completely understood and more research is needed into the prevalence, symptoms and treatments.   In addition, many veterinarians are not aware of the latest research and may not regularly recommend heartworm preventatives for cats.