Heartworm Disease

April is Heartworm Awareness Month, so we wanted to share some information about heartworm disease with you. Heartworm disease can be caused by a single mosquito bite. If an infected mosquito bites your pet, it deposits heartworm larvae into their bloodstream. These larvae then enter your pet through the bite wound and make their way to the heart and lungs. If untreated, the larvae can mature into adult heartworms up to one foot in length and cause serious damage. Mosquitoes (and therefore heartworm disease) are everywhere. Heartworm disease has been diagnosed in all 50 states. It is especially prevalent in states with humid, warm environments, like North Carolina. It can be fatal if untreated, which is why heartworm prevention is very important.1,2

Pets don’t always show symptoms of heartworm disease in the early stages. As the disease progresses, they become more likely to show signs. A dog’s symptoms can include a cough, decrease in activity levels, decreased appetite, weight loss, heart failure, and caval syndrome. While dogs are a natural host for the parasite, cats can also contract heartworms. The disease in cats is much different from in dogs. Cats can either have subtle or dramatic symptoms. They also include coughing, lack of appetite, and weight loss, as well as difficulty walking, fainting, seizures, and sudden collapse or death. Because cats are not an ideal host for heartworms, most of the larvae do not survive to adulthood. Dogs can have hundreds of worms in their body and cats typically will only have one to three adult worms. While the disease is treatable in dogs, it is very costly and there are long term effects to the pet’s health from the parasites even after the worms are gone. Unfortunately, there is no approved treatment for cats. It is a threat to all pets, indoor and outdoor, which is why the American Heartworm Society recommends having your pet tested for heartworms every year and making sure they are on heartworm prevention year-round as well.3,4

There are a few options for heartworm prevention. Cats are limited to monthly oral or topical prevention methods, but, for dogs, you may give a monthly preventative or a yearly injectable. Carpenter Animal Hospital offers both the monthly and yearly preventative options. The ProHeart 12 injection protects your dog from heartworms for 12 months, so it only needs to be given once a year. If you use the monthly preventatives, it is important to be consistent with your dosing. The medication works retroactively, eliminating the heartworm larvae that your pet may have contracted from the previous 30 days.1,2       

If you have any questions about heartworm disease and/or how to prevent it, contact us. We would be happy to help.


1. Zoetis. (2019). It Only Takes One [Brochure]. 

2. Boehringer Ingelheim. (2019). The Protection Dogs Come Running For [Brochure].  

3. American Heartworm Society. (2022). Heartworm in Cats. https://www.heartwormsociety.org/pet-owner-resources/heartworm-in-cats. Accessed March 21, 2022. 

4. American Heartworm Society. (2022). Heartworm Basics. https://www.heartwormsociety.org/pet-owner-resources/heartworm-basics. Accessed March 21, 2022.