You may have heard of heartworms in dogs, but did you know that cats can get heartworms too? Heartworm in cats is less common and somewhat different than it is in dogs. In fact, heartworm disease in cats can be even more dangerous.
What Is Heartworm Disease in Cats?
Heartworm disease is caused by an infection with the parasitic roundworm Dirofilaria immitis. Heartworm larvae enter the cat's body when an infected mosquito bites the cat. Because cats are not ideal hosts for heartworms, (dogs are the ideal host) the larvae may become weakened and succumb to the cat's immune system before causing any problems in the cat. This is why it's somewhat uncommon for cats to develop heartworm disease.
However, if the immature heartworms can survive long enough to travel to the arteries of the lungs, they create an inflammatory response generated by the cat's immune system. This can cause serious complications like heartworm-associated respiratory disease (HARD). Cats may develop chronic lung problems. Others suffer acute distress and need emergency veterinary care. Though uncommon, some cats may collapse and die suddenly.
Signs of Heartworms in Cats
Not all cats will show signs of heartworm disease. Sadly, a small number of cats will show no signs until they suddenly collapse or die. Cats that do show signs of illness typically have respiratory issues like coughing, gagging, labored breathing, wheezing, and asthma-like episodes. Other potential signs include vomiting, loss of appetite, lethargy, and weight loss.
Causes of Heartworms in Cats
Cats get heartworms after being bitten by infected mosquitos. Although outdoor cats are more often infected, indoor cats are still susceptible to heartworms. A mosquito becomes infected after biting an infected animal and ingesting heartworm larvae. The infected animal is often a dog. However, other mammals may be carriers of the heartworm parasite.
In the mosquito, the heartworm larvae begin to mature. When the mosquito bites a cat, the heartworm larvae are deposited on the skin and enter through the bite wound, after which they further develop in the cat's tissues. The larvae migrate through the body, making their way through the bloodstream to the heart, pulmonary arteries, and lungs.
In dogs, the larvae migrate to the heart, develop into adult worms, and begin to reproduce. The adult heartworms eventually cause problems in the dog's heart, lungs, and circulatory system.
In cats, heartworm disease is primarily a lung problem. As cats are not the natural hosts, the larvae can be compromised by the cat's immune system. The presence and death of immature heartworms in the lungs cause the immune system to mount an inflammatory response. Cats may exhibit signs of respiratory illness due to this immune response. In addition, the death of immature heartworms can release toxins and cause further complications like blood clots.
Diagnosing Heartworm Disease in Cats
It is more difficult to definitively diagnose heartworm disease in cats than in dogs. An antibody test may be performed, but this only verifies that the cat has been exposed to heartworms. It cannot confirm the presence of immature worms in the cat.
Chest radiographs (X-rays) and echocardiography can reveal damage to the lungs and heart, consistent with heartworm disease. However, lung changes can look much like asthma and do not necessarily confirm the presence of immature heartworms.
Veterinarians use a combination of testing along with the cat's clinical signs to determine whether or not heartworm disease is present.
Heartworm Treatment for Cats
Unfortunately, there is no specific treatment available for heartworm disease in cats. The treatment for dogs with heartworm disease is not suitable for cats, as it can cause serious side effects. Veterinarians will often recommend getting your cat on heartworm prevention to help prevent future infections.
Surgery to remove heartworms is rarely done, but may be recommended in severe cases. Unfortunately, surgery is risky; many cats will die during the procedure or recovery period.
Supportive care is generally recommended for cats with heartworm disease. Your vet may prescribe some medications to treat symptoms, and others to reduce the inflammation caused by the heartworms. Routine monitoring is also important to assess the cat's lungs and overall health. Heartworms typically live for two to three years in cats (as opposed to the five to seven years in dogs).
How to Prevent Heartworms in Cats
Prevention is key when it comes to heartworm disease in cats. It's more effective to stop the heartworms from infecting a cat than to try to treat a cat with heartworms. There are a number of effective feline heartworm prevention products available. Most are given topically or orally once per month. Ask your veterinarian for information about the best heartworm preventive products for your cat.
Feline heartworms more deadly, difficult to treat. Purdue University.
Keep the Worms Out of Your Pet’s Heart! The Facts about Heartworm Disease. U.S. Food and Drug Administration.
Heartworm Disease in Cats. VCA Hospitals.