Heartworm Disease in Cats
By: Dr. Katie Vance
Published July 1, 2024
Can cats get Heartworm disease?
Yes!
What is Heartworm Disease?
Heartworm disease is a serious and potentially life threatening disease caused by a parasitic worm called Dirofilaria immitus. This parasite grows into foot long, spaghetti like worms that grow in the heart, lungs and surrounding blood vessels. Heartworm disease is less common in cats because cats are not the natural host, so many worms do not survive to adults.
How is Heartworm Disease Transmitted?
Heartworm disease is spread by infected mosquitoes. Mosquitoes must ingest blood that is filled with baby worms called microfilaria from an infected host (ex: dogs, fox, coyote, wolves). These baby worms develop in the mosquito for 10-14 days into infective larvae. At this point, if a cat (or dog) is bitten by an infected mosquito, the infected larvae make their way to the blood stream and grow into adult worms over the next 6 months. Because cats are atypical hosts, few of these microfilaria develop into adults.
What are some symptoms of Heartworm Disease?
More commonly, cats develop Heartworm Associated Respiratory Disease (HARD), which is an inflammatory reaction to the immature worms dying in the pulmonary vessels and lungs. This can present as coughing, wheezing, difficulty breathing, vomiting, decreased appetite, weight loss and lethargy. Adult heartworms can cause chronic inflammation leading to scarring and narrowing of the pulmonary arteries, which causes pulmonary hypertension (increased blood pressure in the blood vessels of the lungs). Adult worms can also affect the ability of the heart to pump properly, leading to heart failure. In some cases, collapse or sudden death are the first symptoms we see.
How is Heartworm Disease tested for?
Heartworm infections are more difficult to diagnose in cats compared to dogs, making it under-diagnosed. Cats have lower worm burdens compared to dogs because they are not the natural host. They are therefore better at killing the heartworm larvae before they become adults. The Heartworm antigen test we use in vet clinic tests for a protein on the FEMALE Heartworm. If there are only 1 or 2 worms, it is less likely there is a female present that will show up positive on the Antigen test. For cats, it is best to test for both Heartworm antigen (detects adult female worms) and antibodies (detects exposure to Heartworm larvae) to allow for a better chance of catching the disease. Your vet may also use radiographs or ultrasound to further assess the heart and lungs.
What treatment is available for Heartworm Disease?
Unfortunately, there is no approved drug for treatment of Heartworm disease in cats. The goal of treatment is to provide supportive and symptomatic care. The hope is that the cat outlives the heartworms, as they typically live 2-3 years in cats. Some cats benefit from small doses of prednisolone to reduce inflammation in the airways. Additional therapies may include IV fluids, oxygen therapy, antibiotics, and cardiovascular drugs. Even if cats clear the infection, they can struggle with permanent damage to their cardiopulmonary systems.
What can I do to prevent Heartworm Disease in my cat?
The American Heartworm Society is now recommending year round prevention because cats have been diagnosed with heartworms in almost every county in Minnesota. Mosquito species are constantly adapting to cold climates and some species survive winter indoors. Up to 1/3rd of infected cats live INDOORS only. Heartworm preventatives available for cats include Bravecto Plus, Revolution, NexGard combo, Heartgard, Advantage Multi, and Centragard. Ask your vet which product would be best for your cat.
