Until recently it was believed that cats could not get heartworms like dogs can.  Unfortunately, we now know that this is not true; cats can in fact get heartworms and even die from heartworm disease.    Remember that heartworm disease in dogs is contracted through the bite of an infected mosquito.  Well, those same infected mosquitoes that bite dogs will also bite cats (and us, as well for that matter) and when they do they inject many tiny baby heartworms into the cat’s body.  

Heartworms much prefer their natural host, the dog, and will live and thrive when injected into a dog’s body.  Inside of a cat’s body the heartworms don’t fare quite as well:  they develop more slowly (it takes them about 8 months to reach adulthood), some may not survive, and the ones that do are disoriented in the feline body and may migrate to odd locations like the brain, fat tissue, and abdomen.  Adult heartworms have a shorter lifespan in the cat (about 2 years) compared to the dog (5 years).

How do you know if your cat has heartworms? 

Initial mild symptoms of heartworm disease may occur about 2-8 months after the mosquito has bitten your cat. At this point the “baby” heartworms have grown into adults, which are arriving in your cat’s lungs.  The lungs respond by becoming irritated and the symptoms are similar to asthma.  You may notice that your cat has a lack of energy; he/she may not want to eat, and may cough, pant, or vomit.  Often these initial symptoms of heartworm disease go un-noticed. 

In fact, most cats with heartworms have only mild symptoms until several years after being infected, when the adult heartworm eventually dies of old age. When this happens your cat may suddenly become very ill and can’t breathe.  The death of 1 single heartworm can cause a life threatening allergic reaction. The lung swells and fills with fluid, making it extremely difficult for the cat to breathe. 

At Bayside, we sometimes hear clients tell of finding their previously healthy outdoor cat dead with no signs of struggle or injury.  Poisoning is often suspected.  These cats were probably victims of feline heartworm disease, and not poisoning.  Cats that die from heartworms may be clinically normal 1 hour before death!   

How can we test for feline heartworms?

Unfortunately, the traditional blood test for heartworms (the one we use for dogs) rarely works in cats.  On physical exam, infected cats may have suspicious sounding lungs.  There may be some changes on bloodwork and in samples of lung fluid.  X-rays may show changes classic for heartworm disease. The absolute BEST way to diagnose heartworms in the cat is with an ultrasound of the heart called and echocardiogram.  

How do we treat cats with heartworms?

 There is no good answer to this dilemma.  The standard drugs used to kill heartworms in dogs can often be fatal to cats.  On the other hand, if untreated the worms will eventually die of “old age” after a few years, causing a sudden respiratory emergency for your cat when they do.  Cats infected with heartworms are often treated with prednisone to help with the inflammation due to worm death over the years.  

Stop heartworms from starting!

            Because heartworms are very difficult to diagnose in your cat, and even harder to treat, we are now recommending monthly feline heartworm preventative medication just as in dogs.  Revolution comes as a liquid which you apply between the shoulderblades and should be given every month year-round.  Revolution will also prevent fleas, ticks, ear mites, certain skin mites, and intestinal worms.