A dog lying in the grass, heartworm prevention

Heartworm Prevention Month

April is Heartworm Prevention Month, and there are important reasons veterinarians across the United States promote heartworm prevention this month and throughout the year. While the risk of heartworm is more prevalent in spring and summer when there are more mosquitos, a pet can get heartworm any time of year.

In this blog, we will cover what heartworm is, how it spreads, and what the best ways are for you to prevent your pet from getting it. 

What is Heartworm?

Heartworm is a disease caused by worms living in the heart of an animal. Mosquitoes transmit heartworm disease to your pet. Heartworm is a potentially fatal disease that can cause heart failure, lung disease, and other organ failures.

Heartworm disease has been diagnosed in all 50 states, meaning that this problem exists regardless of where you live. In Illinois, heartworm disease is found in approximately 1 out of every 100 dogs tested for it.

Once your pet is infected, worms begin to grow inside your pet’s body and can inhabit their heart, lungs, and blood vessels.

How Heartworm Spreads

As mentioned earlier, the mosquito plays an essential role in the heartworm life cycle. Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microscopic baby worms called microfilaria that circulate in the bloodstream.

When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop and mature into “infective stage” larvae over 10-14 days. Then, when the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite wound.

Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5-7 years in dogs and 2-3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

Symptoms of Heartworm

It is more common for dogs to get heartworm, but cats can get it too. A pet can have heartworm without initially showing symptoms. The signs of heartworm disease depend on the number of adult worms present, the location of the worms, the length of time the worms have been in the pet, and the degree of damage that the heart, lungs, liver, and kidneys have suffered.

Most pets initially infected with heartworm do not show symptoms until the disease is more advanced. Following are symptoms to watch out for that could indicate your pet has heartworm: 

  • Occasional or persistent coughing: As the heartworm worsens, your pet’s cough will become more frequent, but you shouldn’t ignore even a mild one.
  • Trouble breathing: As the disease progresses, breathing may become more and more labored.
  • Tiring quickly: With blood flow being blocked or partially blocked, your pet will become tired much more rapidly. 

If you notice any of the above symptoms, whether it could be heartworm or not, bring your pet in for a checkup. 

Treatment of Heartworm

Another reason preventing heartworms is so essential is that the treatment for a heartworm infestation is unpleasant and comes with significant risks for your pet. However, we can successfully treat most infected pets. 

After stabilizing your pet’s condition, treatment takes several steps and may require your pet to stay in our care so that we can carefully monitor them. 

The complete process takes from 6 to 9 months. We must destroy heartworms gradually. Killing them too quickly can be dangerous for your pet. Due to the length and complexity of treatment, treatment can become expensive. Preventing heartworm disease is much less costly than treating it.  

How to Prevent Heartworm

Now that you understand what heartworm disease is and how it spreads, here is what you can do to help keep your pet safe and healthy.

Routine veterinarian visits: Schedule your pet for their annual checkup with us. Performing regular heartworm testing is included in this checkup and is the first defense for keeping your pet safe.

Preventative medication: There are various preventative products that you can use on your dog to ward off mosquitoes and prevent heartworm. You can administer these products orally or topically. The combination of a heartworm preventive paired with an effective flea, tick, and mosquito repellent is most effective for preventing disease. Prevention is far more effective and less costly than treatment if your pet is diagnosed with heartworm. Heartworm medications are available only by prescription, and there are different options depending on your pet and your preferences. Talk to us about which heartworm medication is right for your pet. 

Keep your home mosquito-free: Mosquitoes can also be a threat in and around your own home. Mosquitoes can breed in small amounts of stagnant water. Check out flowerpots, empty containers left outside (buckets, toys), rain gutters, and low-lying areas in the yard. Do your best to remove any stagnant water around your house to minimize their numbers.

Outdoor bug control: Minimizing bugs in your yard is very important in helping to keep bugs away from your pet. You may want to consider using insecticide spray for your yard. Be sure to choose a pet-friendly product and properly follow the manufacturer’s instructions.


Heartworm is a potentially fatal disease, and it is hard to detect in its early stages. Treatment is difficult for pets and comes with significant risks. We cannot overstate the importance of heartworm prevention and heartworm testing for these reasons. Prevention is easy, inexpensive, and pain-free. So, keep your furry loved ones safe and healthy by contacting us and getting your pet on heartworm preventative medication if you have not already done so.


Dr. Stacey Funderburk
Countryside Veterinary Services

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