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  • Writer's pictureArt City Vets

Spring is here! But so are the mosquitoes... and heartworms.

Updated: Apr 20, 2023

Your Philly Vet Art City Vets Philadelphia Veterinarian Dog Heartworm

Heartworm Disease Overview

Heartworm disease is a serious and potentially fatal disease that can affect dogs, cats, and even ferrets. It is transmitted through a bite of a mosquito that is infected with a larval stage of Dirofilaria immitis (scientific name for heartworm). The mosquito becomes infected by having a blood meal from an infected animal. Infected dogs in the community can lead to spread; however, wildlife such as foxes, coyotes, and wolves can also serve as a reservoir for infection. Once an infected mosquito bites a dog, the larva migrates through the skin, maturing into an adult worm over 6-7 months, and eventually lodges itself in the heart, lungs, and associated blood vessels. This can lead to severe, permanent damage and can be fatal if left untreated. The mature adult heartworm can grow up to 12 inches in length (how gross), live for 5-7 years in dogs and 2-3 years in cats –and remember, infected pets are potential carriers for mosquitoes to bite and continue to spread this disease. It is very important for our pets to be receiving year-round prevention and routine testing.

While there is a higher risk of heartworm disease in warmer states with more mosquitoes, it is diagnosed in dogs living in EVERY state of the United States (yes… even Alaska!). For that reason, we strongly recommend keeping your pets on heartworm prevention year-round. Most heartworm preventatives also contain medication to treat against the most common intestinal parasites as well. Intestinal parasites are a very common reason for diarrhea and vomiting – two symptoms most owners prefer to avoid!



In the early stages of heartworm disease, dogs may not have any symptoms. Signs include mild persistent cough, fatigue after moderate activity, reluctance to exercise, decreased appetite, and weight loss. Progressive disease can lead to severe complications such as heart failure, caval syndrome, and ultimately death.


Symptoms of heartworm disease in cats range in severity from subtle to sudden death. These include coughing, asthma-like attacks, intermittent vomiting, decreased appetite, weight loss, fainting, sudden collapse, and/or sudden death.


Signs of heartworm disease in ferrets develop rapidly after the adult infection has developed as a ferret’s heart is very small. A single worm in their tiny heart can cause significant damage and block blood flow. Symptoms include fatigue, decreased appetite, wheezing, cough, but more often respiratory distress (open-mouth and rapid breathing, pale blue gums, significant coughing).


“Heartworm Basics.” American Heartworm Society, Jan. 2020,

“The Facts about Heartworm Disease.” U.S. Food and Drug Administration, FDA, Aug. 2019.

“Heartworm Disease.” Heartworm Disease, American Veterinary Medical Association,

Author: Dr. Laura Zemanian

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