I hope you enjoyed the recent blog on canine heartworm disease. We know that “every dog has his day” with dogs frequently in the news, but shouldn’t every cat have an equal opportunity? Let’s focus on America’s largest pet population and take a look at feline heartworm disease. First, we’ll dispel a few feline myths.
False assumptions regarding feline heartworm:
- Cats don’t get heartworms. Yes, they do. Feline heartworm infection exists everywhere canine heartworm is present. And heartworms impact lots of cats. In fact, heartworms affect cats more than FIV or Feline Leukemia virus does.
- Cats that live indoors don’t need heartworm preventive. Yes, they do. Cats don’t need to go outside to be infected. Mosquitoes that fly through an open door or window can infect your cat.
- Cats can’t die of heartworms. Yes, they can. Often this death is very sudden and without warning.
- Cat heartworm disease is similar to the dog illness. No, it’s not. Dogs get sick later in the heartworm infection while cats may show symptoms very early in the disease process. Cats may have intense pulmonary symptoms or vomiting. Sometimes heartworm signs resemble feline asthma. And sometimes there are no symptoms at all.
- Cats don’t need to be tested for heartworms. Yes, they do. There is an antigen test available, but your veterinarian may need to perform other tests such as radiographs or cardiac ultrasounds to arrive at a diagnosis.
Cats vs. Dogs—The difference between feline and canine heartworm disease
Cats are definitely susceptible to heartworm infection. It has been estimated that feline infection rate is around 20% of the canine infection rate in a given area. But feline heartworm disease is different than the canine infection. First of all, cats usually have fewer adult worms than dogs. Plus, these adults are typically smaller and don’t live as long as canine heartworms. Even so, feline heartworm infection can be very serious.
How cats handle heartworms
Cats respond differently to heartworms because they have a unique immune system that includes a special defensive blood cell called a pulmonary intravascular macrophage (PIM). PIMs are located in very tiny blood vessels called capillaries. Cats are the only carnivore that have PIMs. Dogs don’t have them.
PIMs are part of the feline defense mechanism and are called to action when the feline body recognizes the presence of a heartworm infection. PIMs become outraged at the intrusion of the heartworm parasites into their home and work to evict them. PIM’a initiate an inflammatory response that is harmful to the parasite. That’s the good news. The bad news is that the PIM response can harm the cat as well.
How heartworms handle cats
Here’s how the heartworm outwits the cat: The heartworm is a smart parasite and realizes that if it allows PIMs to continue the eviction efforts, the cat will be adversely affected. If the pulmonary inflammation becomes too severe, the cat will die. That means the heartworm loses its home. In defense, the heartworm manipulates the cat’s immune system by suppressing PIM response, relieving the inflammation and restoring the cat to respiratory health. As long as adult heartworms are alive, so is the cat. Happy heartworm…happy cat.
But, as adult heartworms die of old age, PIM function is restored, inflammation re-occurs, and the cat has potentially fatal lung problems once more. Moreover, pieces of the dead heartworm may clog blood vessels and cause death by embolism (similar to a blood clot). Either way, heartworms can be fatal.
How veterinarians handle cats and heartworms
To make matters worse, unlike dogs, cats don’t have the benefit of an approved medicine to kill adult heartworms. Veterinarians can treat the symptoms of heartworm disease, but can’t “cure” it. This makes diagnosis even more important. Your cat’s doctor can prescribe helpful therapy if your cat tests positive for heartworms. See our article on heartworm treatment in cats and dogs.
How cat owners can prevent heartworms
Lack of approved adulticidal treatment makes preventing heartworms in cats even more imperative. Luckily, there are many approved feline heartworm preventives on the market. These medications should be administered every 30 days year-round in any area of the nation where canine heartworms exist.
Sadly, less than 1% of cats are tested annually and only 4% of cats currently receive monthly heartworm medication. Raise these statistics by having your cat tested and giving him the medication he needs to ward off heartworm infection.
Don’t let your cat be the victim of false assumptions.
Do you know of a cat that has been affected by feline heartworms?