Kingsbury Animal Hospital

420 North Skinker Blvd.
Saint Louis, MO 63130


Kingsbury Animal Hospital
Feline Heartworm Disease
What are Heartworms?
Heartworm Disease is caused by the parasite Dirofilaria immitis. Heartworms are parasites that live in an animal’s heart and lungs. They are transmitted when an infected mosquito injects heartworm larvae into a dog or cat’s tissues. These larvae then penetrate through the pet’s tissues, eventually reaching the vascular (blood) system. 
I thought Heartworm Disease was a Canine Disease?!
Veterinarians used to think that heartworm was primarily a canine disease, but many studies have shown us that in areas where dogs are at risk, cats are also at risk. Dogs are the preferred host for heartworms, but sometimes infected mosquitoes will infect cats as well. For example, heartworms in dogs are considered endemic in the Midwest, meaning that dogs not on heartworm prevention are at great risk for acquiring this serious parasite. Studies indicate that the prevalence of heartworm disease in cats is 5-20% the rate of unprotected dogs for any given area.
Heartworm in Cats…actually a RESPIRATORY Disease!
The term is actually a misnomer when talking about cats. Unlike dogs, feline heartworms mostly affect the lungs.   The acronym “HARD” (Heartworm Associated Respiratory Disease) is used to describe the disease in cats.   The vast majority of heartworm symptoms are caused by the massive immune response mounted by a cat’s body in response to the presence of juvenile worms or death of adult worms.
Signs and Symptoms of Feline Heartworm Disease
Cats with heartworm disease can experience either acute disease (meaning the symptoms can occur suddenly and be quite severe) or chronic disease (meaning the symptoms are on-going, and the patient has long term disease).
Acute symptoms: vomiting and diarrhea, rapid heart rate, collapse, difficulty breathing and increased respiratory rate, convulsions, fainting and sudden death.
Chronic symptoms: coughing, wheezing, vomiting and diarrhea, difficulty breathing and increased heart rate, lethargy, anorexia (not eating well) and weight loss.
Because many of the symptoms are similar, many cats with heartworm disease can be mistaken for having asthma or allergic bronchitis. Also, it is important to note that some cats with heartworm disease display no symptoms, depending on the stage of their disease!
Indoor cats vs. Outdoor cats
We know that outdoor cats are at risk for heartworm disease, as they are at risk for a bite from a mosquito. Not all mosquitoes carry the parasite, but some do.   We recommend that ALL indoor-outdoor cats and all outdoor cats be on a monthly heartworm preventive. 
For indoor cats, there still can be a risk of developing a heartworm infection. Some studies show that a significant number of cats diagnosed with heartworm disease were strictly indoor. However, it is probable that a strictly indoor cat comes in less contact with mosquitoes than their outdoor counterparts. If you want to be as proactive as possible, then heartworm prevention or indoor cats is also indicated!
Prevention, Treatment and Diagnosis of Feline Heartworm Disease
We recommend routine monthly heartworm prevention for cats. Prevention is very important, as it is very difficult to diagnose feline heartworm disease. 
We have two types of feline heartworm prevention: Revolution and Heartgard. Revolution is a once monthly topical medication that is also a flea, ear mite, hookworm and roundworm preventative. Heartgard is a once monthly chewable flavor tablet that also protects against roundworms and hookworms.
Treatment for feline heartworm disease is similar to treatment for feline asthma and includes anti-inflammatory medications. However, because the disease can lead to irreversible lung disease, it is important to consider a preventative for your cat!
Sources: American Heartworm Society 2007 Feline Guidelines and KNOW Heartworm Campaign