Fred Thomas is religious about giving heartworm preventative to his three dogs.  On the first of every month, Fred breaks open a new package of medication and every dog gets their monthly treat.   Looking over at his cat, Fred grabs the kitty treats and tosses a few to the feline member of the pack.   What Fred doesn’t realize is that he is leaving his cat unprotected from a deadly killer.

Like Fred, most cat owners are unaware of this often fatal disease.  Heartworm disease was found in cats as early as the beginning of the 20th century, but few cat owners or veterinarians were concerned about it.    Recent studies have shown that 26% of cats from the Gulf Coast have signs of heartworm infection at some point in their lives and 10% have actual adult worms.  These prevalence rates are significantly higher than rates for Feline Leukemia or for the Feline Immunodeficiency Virus.  Yet, according to the American Heartworm Society, only about 5% of cat owners use any sort of heartworm preventative for their cats!  Like dogs, cats acquire the parasite from mosquitoes but this is when any similarity ends!  

Heartworms continually evolve to exist in their canine hosts, but cats are abnormal hosts and these heartworms will live stunted and shortened lives.   You might think that this is a good thing, but due to our cat’s strong immune systems, heartworms actually can cause more serious and severe disease than they do in dogs.   It is not unusual for a dog to live for years with 20, 30, or even 50 worms in their heart.   But a cat with a single heartworm can die suddenly, often with no apparent clinical signs whatsoever.  In addition, your “inside only” kitty is just as susceptible as the outdoor tomcat.

Upon infecting a cat, the heartworm larva will travel to the blood vessels of the heart and lungs, where it will grow to be about two inches long.   At this time, cats may exhibit respiratory symptoms that are often misdiagnosed as bronchitis or asthma.   Veterinary scientists studying heartworm disease in cats have given this stage of the disease a name:  Heartworm Associated Respiratory Disease, or HARD.  

As the heartworms mature, signs of their presence will often diminish.   In fact, evidence suggests that the live heartworms can actually suppress the cat’s immune function and the cat appears to tolerate the infection.   However, when the mature worms start dying, massive inflammation can occur, leading to acute lung injury and even sudden death.   Your cat can literally die within an hour!

So, what signs should you look for to keep your cat safe?   Cats with heartworms may exhibit difficulty breathing, coughing, vomiting, weight loss, sudden collapse, or even sudden death.  Because this disease can cause such a terrible outcome in a short period of time, your veterinarian should immediately examine any cat exhibiting these signs.  Tests are available to screen for heartworm disease, but again, unlike dogs, testing cats is a complex, often confusing, endeavor.  To make matters even worse, there is no effective or approved way of treating adult heartworms in cats.  So prevention is really the key!

And on that front there is good news!   Heartworm preventatives are available for cats and are as easy to give as the medications designed for dogs.   These preventatives are available in both oral and topical formulations and your veterinary staff can help you choose the right one for your pet.   Your veterinarian can also help you make sense of heartworm testing options for your cat.   Although the Heartworm Society does not mandate testing cats prior to using a preventative, it is recommended as a baseline for future reference.

Preventing heartworm disease in cats is only one step to helping our feline friends live long and healthy lives.   Twice yearly physical exams, blood tests and appropriate vaccinations can all do their part to insure your cat’s health.