Chasing Heartworms in Wisconsin

Let’s Talk Heartworm!


It’s that time of year again – birds are coming back, snow is thawing, the days are longer and Heartworm Season is officially under way! Most of our canine clients will bring their pet in at some point during the year for the all-important heartworm blood test and heartworm prevention. However, if you talk to them many don’t really understand why they do it. We are fortunate to be in a part of the country where Heartworm disease is less common (compared to the south for example), so is it really a big deal? To answer that, let’s ask one of our patients – Chase!


Chase and Emily - Heartworm Disease Dogs - Oakview Vet Plover WI
Chase and one of his nurses, Emily


Chase is a 4 year old Portuguese Water Dog owned by a fabulous couple in Portage County. After the loss of their previous dog they decided to adopt a young adult from a breeder in Illinois. It is important to note that to our knowledge, Chase had never left the state of Illinois prior to his adoption. As soon as they brought Chase home they made an appointment for us to examine him and perform a heartworm test in order to start his monthly prevention. Imagine our surprise and dismay when that test was positive!

Below is a video taken through a microscope. The red blobs are red blood cells, and the string-like movements among them are baby heartworms. This is just a single drop of blood! Imagine them wiggling through the whole blood stream!


Although Chase’s owners were upset, they are people of action (lucky Chase!) and we immediately collected the information we needed to safely treat Chase for this disease. Blood was collected to be sure there were no other problems (such as a liver or kidney issue that could delay treatment). X-Rays showed that his heart was enlarged from the worms, so they all took a trip to the Veterinary School in Madison for an echocardiogram (an ultrasound of his heart). Fortunately his heart was not damaged! Finally, the special (and expensive) drug used to kill the heartworms was ordered and administered (Chase would like to say that he did NOT like that part!). Before we get to the end of the story, let’s review a little about heartworm disesase.


Heartworm Disease - Dogs - Oakview Vet Plover WI provides this enlightening map showing that Wisconsin is in an area of risk for heartworms.


So what is Heartworm disease anyway?

Heartworm disease is exactly what it sounds like. It is a parasite (worm) that lives in the right upper heart (the right atrium) and the large blood vessel that attaches to the atrium (the vena cava).  They grow to be up to 12 inches long and look a lot like spaghetti. Because they live in the heart (and vena cava) they will interfere with blood flow, cause heart enlargement, lung disease and ultimately many dogs with heartworm will die from the disease. There are many excellent websites where you can go to find even more information; The American Heartworm Society has an excellent site!


Heartworm dog canine - Oakview Vet Plover WI
Actual Heartworms found in a dog’s heart


How can a mosquito spread a worm?

Because the adult worms live in the blood stream, when they have babies (microfilaria) those babies are also in the blood stream! A mosquito bites an infected dog, sucks up blood and baby heartworms and then bites your dog effectively transmitting the disease. It is important to note that ONE MOSQUITO can effectively transfer several microfilaria! It only takes ONE BITE!


heartworm life cycle dogs - Oakview Vet Plover WI
The Life Cycle of Heartworm


Is it really a problem in Wisconsin?

Unfortunately, after a decrease in reported cases of heartworm disease around 2010, heartworm is on the rise again in our area as well as in other parts of the country. Remember how Chase came here from Illinois? This shows that heartworm is also originating from farther north.

Several factors contribute to this increase in incidence:

  • a mobile society where people may move from Texas to Wisconsin and bring a heartworm positive dog with them
  • wildlife such as foxes and wolves may carry the disease
  • failure to treat positive dogs – treating a dog with heartworm is expensive (just ask Chase’s new mom and dad!) and some people just can’t afford it. That means a positive dog may spread heartworm for months or years!
  • failure to prevent the disease – this happens most often in small, primarily indoor dogs. We often hear people say, “He only goes outside to go potty!”. While a primarily indoor dog definitely is at a lower risk than an outdoor dog, who among us doesn’t get mosquitoes in their house at times!?
  • failure to prevent the disease ALL of the time. In Wisconsin, we get a short break from mosquitos that transmit the disease, however, we have clients that vacation south (south being south of the Wisconsin border!) and forget to prevent the disease there!
  • 2017 was a high year because of the mild winter and high rainfall. We are expecting this trend to continue into 2018


Isn’t prevention expensive?

Not really! Depending on the size of your dog, heartworm prevention may be as little as $4.00/month. And even in larger dogs where it may be higher (depending on which prevention you choose), it is usually less than $15/month ($0.50/day) and most of us spend that on a soda, candy bar or bag of chips! For most dogs the cost of preventing heartworm disease THEIR ENTIRE LIVES is less than treating it one time!


heartworm prevention - Oakview Vet - Plover WI
A selection of products available to prevent heartworm, from monthly chewable tablets to a 6 month injection.


So what happened to Chase? Instead of being able to run and play and go for long walks, Chase was in for several months of testing, treatment and exercise restriction. Fortunately for him, his new people were dedicated to helping him recover and he is now doing well! However, it was a long road for all of them and they are hoping to spare some of you the same heartbreak they experienced. As of December, Chase is heartworm free! He says he can’t wait for this summer!!

Chasing Heartworms - Oakview Vet - Plover WI
Chase can’t wait to run and play!




Dr. Scott is a 1986 graduate of Michigan State University. She has advanced training and a special interest in avian, exotic and feline medicine.
A member of the American Association of Feline Practitioners and the Association of Avian Veterinarians, she is also associated with Houserabbit Society and Association of Exotic Mammal Veterinarians.
Dr. Scott and her husband have two children as well as two cats, one dog, and four horses.

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