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Pet Heartworm Prevention

male and female with a dog

Written by Dr. Tracy Williams, DVM

What are heartworms? How do you prevent your pet from getting heartworms? Dr. Williams, a Hello Ralphie veterinarian, walks pet parents through what heartworms are and pet heartworm prevention tips.

What are Heartworms?

Heartworms are parasites that take up residence in the heart and lung tissue of your pet. Veterinarians know of heartworm infections in dogs, cats, and even in ferrets. This is very scary disease and can cause irreversible damage to the heart and lungs of a pet, but the good news there are a lot of ways to prevent your pet from getting heartworms. 

How Do Pets Get Heartworms?


To better understand heartworms, let’s first discuss their life cycle. Baby heartworms are called microfilaria and go through several stages of maturation. 

In the first stage, they are found in the bloodstream of the infected animal.

When a mosquito bites the infected animal, the microfilaria (larva) gets into the mosquito. Here, the larva develops into the infective stage. This is when the infection becomes contagious to other animals.  

When the mosquito bites the next animal, the larva travel into their tissue for further development.  This next maturation can take 2 months. From there the larva travels to the bloodstream on its way to the heart to become a mature adult (4-5 months). Inside the heart, mature adult heartworms can live up to 7 years.

Heartworm Symptoms in Dogs and Other Pets

As you can imagine, in the beginning of a heartworm infection, there are very few symptoms, especially with dogs. In fact, it can take up to six months after infection for our tests to show a positive infection in dogs. Conversely, in feline patients, one of the first noticeable symptoms may be death. 

dog lying down

Since veterinarians are able to diagnose more heartworm cases in dogs, we can present a more conclusive set of symptoms. One of the first symptoms seen is coughing. With the worms lodging in the heart and lungs, it causes irritation in the lung tissue and causes the heart to work harder to pump blood.  This leads to the heart getting larger and pushing on the trachea. Both contribute to the coughing. With the increased work and the parasites creating more turbulence in the heart, your pet becomes more likely to have a blood clot which can lead to a stroke and possibly death.  

As the disease progresses and the heart continues to overwork, we start to see weakness and exercise intolerance, leading up to heart failure. Unfortunately, once the heart is damaged from the parasites, it cannot be fixed. We can only treat and manage the symptoms. If left untreated, this can be fatal.

How to Diagnose Heartworms in Pets

The most common way to diagnose heartworms is with a simple blood test that detects residue released from adult heartworms into a pet’s bloodstream. To run the test, veterinarians just need a few drops of blood from a pet. Results are typically available in 10 minutes.

Another test is to look for microfilaria under the microscope. Veterinarians will often run this test after a positive test result to confirm the infection.

If your pet has recently been diagnosed with heartworms, and you have questions, feel free to set up an appointment with a Hello Ralphie veterinarian and we would be happy to talk about your options. 

Pet Heartworm Prevention is Important

A common thought from pet parents is thinking that since their pet barely goes outside, their pet cannot possibly get heartworms. Not true!

Mosquito studies show that seven out of ten mosquitoes, in an area with a heartworm -positive dog, test positive for heartworm larva. There are 80 different species of mosquitos around the world known to carry heartworm larva, and those species feed at different times of day. That means that your pet can be exposed at any time of the day, going out just to potty.  

Since we know that heartworms have been diagnosed in all 50 states, there is a chance of exposure no matter what state you live in. Some states are at a much higher risk than others. The American Heartworm Society has partnered with veterinary clinics across the USA to come up with an incidence map to try and highlight the areas of greatest risk. Unfortunately, from the report in 2016 to 2019, heartworm incidence increased by 20%.

dog receiving tablet

Pet Heartworm Prevention Medication

There are several different heartworm prevention options available to pet parents.

  • Heartworm Prevention Tablets: There are several different kinds of tablets that can be given monthly, some even containing flea prevention, and one also prevents against ticks.
  • Heartworm Prevention Topical Treatment: For topical prevention, pet parents can apply the treatment to the skin, behind the neck of the pet, once a month.
  • Heartworm Prevention Injections: There is even an injection that can be given every 6 months or once a year. 

With all the options available, the choice comes down to what part of the U.S. you live in, and how active you and your pets are. For example, if you take your pet hiking or camping, versus the pet who goes outside only to use the bathroom, you may want to consider different options. Hello Ralphie veterinarians are here to help!

Pet Heartworm Treatment

Once a pet tests positive for heartworms, there is only one approved treatment method. This method is only for dogs, as there is no approved treatment for cats and ferrets. The heartworm treatment involves a series of painful injections in the back muscles and medications over several months. This treatment is very expensive, so it is much easier to prevent heartworms than to treat them. 

If you still have questions, feel free to make a virtual veterinary appointment with a Hello Ralphie veterinarian. If you feel that your pet may be experiencing symptoms and you want to test your pet for heartworms, please contact your local veterinarian to set up an exam and heartworm test.

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