Heartworm Disease

Image courtesy of the american heartworm society.

Image courtesy of the american heartworm society.

What is Heartworm Disease?

Heartworm disease is a serious and potentially fatal disease caused by a parasitic roundworm (Dirofilaria immitis) that can affect our animals. The disease itself is transmitted by the bite of an infected mosquito that has previously bitten a heartworm positive animal. 

What Animals Can Get Heartworm Disease?

Domestic and wild animals are able to contract heartworm disease. Mammals such as coyotes, wolves, dogs, cats, and ferrets are the more common animals to become heartworm positive. Dogs are the ideal natural host. Cats on the other hand, handle the disease slightly differently. Since a cat is not the ideal host, the diagnosis and management is different. Dogs host a larger amount of mature worms where as cats host very few, but can get very ill from the small amount.

Photo by BanksPhotos/iStock / Getty Images

Photo by BanksPhotos/iStock / Getty Images


Each year at the time of your pet’s annual exam (or throughout the year due to varying due dates) we offer heartworm testing in a few ways. Through our laboratory, we offer a panel (for junior or senior pets) that includes a heartworm test with blood work, just a heartworm test, or heartworm testing in clinic. What a heartworm test looks for is the presence of microfilaria (baby worms) in the blood. By drawing a small amount of blood from your pet, we are able to tell if there is a presence. If the test is positive for microfilaria, it means that there are adult heartworms that are reproducing. If the test is negative, then there were no microfilaria to be detected.




How is it Transmitted?

When a mosquito bites a heartworm positive animal and takes a blood meal, it picks up the microfilaria (baby worms) that circulate throughout the blood stream. The mosquito itself then serves a very important role in the life cycle of heartworms. After the ingestion of the microfilaria, the mosquito plays host to the development and maturation of the microfilaria to their infectious larval stage which takes place in about a two week period. After that maturation period, when an infected mosquito takes another blood meal from another animal, the larvae are then deposited onto the skin and enter through the bite wound created by the mosquito. From here, the larva migrate through their new host for the following weeks to complete their journey in the heart, lungs and associated blood vessels where they mature to adults and begin breeding. In order to breed, there has to be a male and female heartworm present to produce microfilaria. The microfilaria itself is not a heartworm yet – it needs to go through the intermediate stage of the mosquito to mature into a larval stage.


Hearing that your pet came back heartworm positive is no pet owner’s dream. Fortunately, for dogs there is a FDA approved drug treatment. There is not an approved drug treatment for cats but with supportive veterinary care, we can establish a long-term management plan.


Fortunately, heartworm disease is almost 100% preventative. We offer a variety of products that are administered monthly. Ask your veterinarian which product is the best option for your pet.

Heartworm disease has been diagnosed in all 50 states. Prevention is to be administered year round to prevent exposure. If there are one or more missed doses of preventative, a heartworm test needs to be checked prior to restarting a preventative.  

For more information on the topic, please ask your veterinarian or visit the American Heartworm Society.