A lot of pet parents have always seen heartworm as a disease that primarily affects dogs. While it's true that dogs are at a greater risk of contracting heartworm, it's not true that cats are immune. Cats can - and do - get heartworm.
The Trouble With Feline Heartworm
Feline heartworm is far more difficult to diagnose than canine heartworm. It's a complicated process, but because cats have a higher natural immunity to heartworm, fewer adult heartworm are likely to survive in their bodies even when infected. Live heartworms in cats are often able to suppress any clinical signs of their existence. In one study, more than 28% of all cats infected with heartworm showed any clinical signs at all. Diagnostic testing (antigen and/or antibody) for feline heartworm is available, but far less reliable than the canine versions of the tests. It's still important, though, to have your veterinarian run a feline heartworm test if you have any reason to suspect your cat has contracted the disease.
Cats and Their Response to Heartworm
Cats become infected with heartworm parasites the same way most animals do: through mosquitoes. If mosquitoes are present, any cat not currently on heartworm preventatives is at risk. The good news is, cats' bodies are far better at fighting off a heartworm infection than many other animals'. Unlike dogs, cats can "self-cure" heartworm depending on the type and severity of the infection, and around 80% of infected cats do within 2-4 years. This can happen at any point once infected, but usually occurs when the cats antibodies force out any larval parasites. Once adult worms have matured, they can also be suppressed by a cat's own immune system. Though it sounds like a magic cure, this type of "healing" isn't without its risks.
When a cat self-cures a case of heartworm after the worms have reached adulthood, those worms have already done significant damage to the small blood vessels in the cats lungs. It's also possible that as the adult worms die off, the degenerating parasites will cause an inflammatory response that actually blocks blood flow to the cat's lungs. This can be fatal - and it can be caused by just one single heartworm.
Detecting and Preventing Heartworm in Cats
It's important to have your cat tested for heartworm at least once a year, even if she's on a preventative medication. Applying heartworm preventatives to an infected cat can actually do more harm than good. It's also important to watch out for any clinical signs of heartworm including fast breathing, trouble breathing, or coughing. Take these symptoms seriously and call a vet if your cat is experiencing them! Rarer but more serious symptoms might include vomiting, collapse, or even neurological issues. A cat's best defense against heartworm disease is prevention. Ensuring your cat is on a monthly preventative is incredibly important. If you adopt a shelter cat, it's critical to have her tested for heartworm as soon as possible...only about 25% of shelters test cats for the disease.
If you have questions for your vet about the best way to prevent heartworm disease in your cat, don't wait to ask. Unfortunately, most cat owners who lose their feline companions to heartworm had no idea anything was wrong until it was too late.