Cats Get Heartworm Too

How are heartworms transmitted??  Via mosquito bites. So why the general assumption that dogs can get it, but not cats?  Maybe we think most cats are indoors, that they aren’t at risk? But mosquitoes can come inside and bite you, so why can’t they bite your cat?

One weekend morning, a close friend of mine sent a video of her cat laying on its side panting, piles of vomit around the house.  He was a recent rescued adult neighborhood cat. They took him in, got him neutered, vaccinated, and not surprisingly, tested positive for FIV (Feline Aids).  Cats can live a long life with FIV, so this was not a concern. He was now indoors and the sweetest cat ever and on monthly prevention (flea/heartworm). So as a vet, any open mouth breathing in a cat turns on emergency mode.  By the time a cat tells you they are in respiratory distress, any little trigger can push them over the edge. I told them to come straight over, but warned that some cats pass away on the ride. We were able to perform some x-rays and get a little blood.  He tested positive for heartworm antigen. He seemed to stabilize, but unfortunately, passed away a couple of hours later from a probable thromboemboli (blood clot).

Cats are unique in that they show HARD - Heartworm Associated Respiratory Disease.  This occurs when a cats immune system attacks the maturing larvae, causing severe inflammation in the lower airways.  This looks like and can be misdiagnosed as asthma or allergic bronchitis. As the parasite dies, we can see further inflammation or even thromboembolism (obstructed blood vessel) that can be life threatening.  Sometimes this clot dislodges quickly and we can see sudden death. Other times we can see respiratory signs such as coughing, heavy breathing, or gasping/distress. An unusual sign we can attribute to heartworms is vomiting.

Unfortunately, heartworms can be deadly in cats, but we have a hard time testing/diagnosing them.  Their immune response is so strong, that most larvae never reach adulthood. To get a positive heartworm antigen test used in dogs, there needs to be a least one adult female worm.  So if there are only male worms, or immature worms, we will get a negative test. We also have an antibody test for cats. This shows exposure to heartworms some time in the past, but not necessarily acute disease.  If a cat shows up positive on an antibody test, further diagnostics should be pursued.

But there is good news.  Heartworms can be prevented!  There is monthly medication for cats, just like dogs. There are pros and cons of each medication, but I prefer a prevention that lasts through the month.  This means the larvae are killed every day through the month, to prevent larval maturation that leads to the inflammatory response. You should always discuss options and risk factors with your veterinarian to see what works best for your pet.

Dr. Leah Wulforst, Riverside Veterinary Clinic, Knoxville, TN

Here are some information links regarding Heartworms in cats:

Veterinary Partner:

The American Heartworm Society

Cornell University Pet Health Center