Heartworm Disease in Cats
By Sherry Blackmon
Are cats at risk for heartworm disease?
Yes. All unprotected cats are at risk of heartworm disease if they live, or spend time, in a region where mosquitoes transmit larvae of Dirofilaria immitis (the canine heartworm). Heartworm disease has been reported in all 50 states and the Southeast has the highest prevalence of heartworm disease in the U.S. When comparing the same geographic area, the prevalence of heartworm infection in unprotected cats is estimated at 5-20% of the canine population. , A single bite from an infected mosquito can infect your cat. Mosquitoes easily gain access to homes through doors, pet doors, windows and small tears in window screens that may go unnoticed. Once inside your home, they can persist for a long period of time which is another reason year-round heartworm prevention is recommended.
Is my kitten at risk for heartworm disease?
Yes. Kittens and adult cats are equally at risk for heartworm infection. The American Heartworm Society recommends that kittens be on heartworm prevention as early as the product label allows and all kittens should be on heartworm prevention no later than 8 weeks of age.
How can I protect my cat/kitten from heartworm disease?
The American Heartworm Society recommends pet owners to “think 12.” This means every pet should be tested for heartworm disease every 12 months and that all pets should be on heartworm preventative 12 months of the year. HEARTGARD® Chewables for Cats (ivermectin) (Merial)
- Advantage Multi® Topical Solution for Cats (imidacloprid/moxidectin) (Bayer Animal Health)
- Interceptor® Flavor Tabs® for Dogs & Cats (milbemycin oxime) (Elanco)
- Revolution® (selamectin) (Zoetis)
How do heartworm prevention medications work?
Heartworm preventatives kill larvae at specific phases of their lifecycle, including larvae transmitted by infected mosquitoes. Heartworm preventatives do not kill adult heartworms. Larvae may molt into the adult heartworm inside your cat in as little as 51 days 3 under ideal environmental conditions, such as those found in the Southeast. This is why it is so important that heartworm prevention be given every month without missing a dose.
Are there any other benefits of heartworm prevention medications?
Yes. Many heartworm disease preventatives kill fleas and intestinal parasites that cause disease in cats or that may be a zoonotic risk for your family. Discuss the best prevention product for your cat and household with your cat’s veterinarian.
Are the medications difficult to administer?
Most cats tolerate administration of heartworm prevention medications quite well. If your cat is fractious or hides when suspicious of medication, try offering a highly desirable food treat immediately before and after administration. Your cat’s veterinarian may also suggest a different prevention medication that better suits your cat’s preferences.
What are the clinical signs that my cat may have heartworm disease?
In some cases there are no symptoms at all before death. Sudden death occurs in 10-20% of infected cats 1 Symptomatic cats may show signs that include the following: 1,3
- Heartworm Associated Respiratory Disease (HARD)
- Asthma-like attacks
- Difficulty breathing
- Vomiting unrelated to eating
- Decreased appetite
- Weight Loss
- Neurological signs
How is heartworm disease diagnosed in cats?
Veterinarians typically use either an antigen or an antibody test. Depending on the test used, results may be available within minutes. However, the tests are not as sensitive as they are in dogs. This means there is a greater risk of obtaining a false negative test result. Other diagnostic modalities also exist. Your veterinarian will diagnose heartworm disease using a combination of your cat’s history, physical exam and diagnostic testing.
What are the treatment options for cats diagnosed with heartworm disease?
There is no cure or drug approved for treatment of heartworm disease in cats. The drug therapy used to treat dogs with heartworm disease cannot be used safely in cats. Supportive therapy may help manage symptoms associated with heartworm disease and make your cat more comfortable, but there is no therapy available to kill adult heartworms in cats.
What is the prognosis of a heartworm positive cat?
[i] Maddie’s Fund. An overview of feline heartworm diseases. Available online at http://www.maddiesfund.org/feline-heartworm-disease.htm?p=9eb1511d-cae0-45db-d754-2481de80ce56. Accessed on September 2, 2016.
 Kentucky Veterinary Medical Association. Canine and Feline Heartworm Disease. Available online at:
http://c.ymcdn.com/sites/www.kvma.org/resource/resmgr/imported/4-10-Canine%20and%20Feline%20Heartworm%20Disease.pdf. Accessed on August 21, 2016.
 Litster AL, Atwell RB. 2008. Feline heartworm disease: a clinical review. J Fel med Surg, 10: 137-144.
 Maddie’s Fund. An overview of feline heartworm diseases. Available online at http://www.maddiesfund.org/feline-heartworm-disease.htm?p=9eb1511d-cae0-45db-d754-2481de80ce56. Accessed on September 2, 2016.