Heartworm Disease Highlights:

  • Dogs and cats can get heartworms.
  • Mosquitoes transmit heartworms, and transmission only takes 1 mosquito bite.
  • Yes! Mosquitoes sneak indoors. In fact, some may even overwinter inside.
  • While heartworm disease can be treated in many dogs, the arsenic-based compound can cause side effects, some of which may be severe.
  • Heartworm treatment is much more expensive than heartworm prevention!
  • There are no approved heartworm treatments for cats.
  • Think12 – Heartworm disease can be prevented by using heartworm prevention year-round!
  • Heartworm disease is in Guilford County. According to the CAPC website, in 2015, 1 out of 82 dogs tested positive for heartworm disease.
  • Learn more about the symptoms and consequences of heartworm disease in dogs and cats.

​Lawndale Veterinary Hospital recommends that every dog and cat receive year-round heartworm prevention. 


How to Protect Your Pet:

  • Administer heartworm prevention year-round to all dogs and cats.
  • Create a habit you can remember – pick a date, and stick with it.
  • Set reminders. Sign up for email reminders from the companies who make the heartworm prevention, set a reminder on your phone, or put it in your planner.
  • For oral preventives, verify your pet swallows the medication. Also, if your pet vomits after administration, the medication may not have been absorbed. In this case, contact us so we can help you decide whether to re-dose.
  • Did your pet gain or lose weight? The dose may need to be adjusted!
  • Do not adminster heartworm prevention to your dog until he or she is tested and found to be negative for heartworms. Giving heartworm prevention to a heartworm positive dog can cause a life-threatening reaction.
  • All dogs should be tested for heartworms every 12 months.

Why do we test for heartworms in dogs already receiving year-round prevention?

At Lawndale Veterinary Hospital, we recommend annual heartworm testing for all dogs, even those receiving regular heartworm prevention. Here are some reasons that support that recommendation:

  • The test we use at Lawndale not only tests for heartworm disease, it also screens for exposure to 3 different tick-borne diseases.
  • Giving heartworm prevention to a dog with heartworms can make them very sick.
  • Sometimes monthly doses are accidentally delayed, missed, or forgotten.
  • If the topical prevention (on cats) was not applied correctly, it may not be fully effective.
  • Sometimes dogs will spit out or vomit up their monthly dose before it was fully absorbed.

​It is important to note that the heartworm test will not show a heartworm positive result until 6 to 7 months after the dog became infected. Therefore, for any dog that has been off heartworm prevention and tests negative at the first test, we should retest again 6 months after the initial test to confirm the dog is truly negative.

My cat stays inside all the time, why do I need to use heartworm prevention?

  • Mosquitoes can come inside.
  • Indoor and outdoor cats have been infected with heartworm disease.
  • Cats can show signs of respiratory disease as soon as 3 months after a heartworm infection.
  • There are zero approved treatments for heartworms in cats.​

Heartworm Lifecycle: 

  • Mosquitoes acquire heartworm larvae when feeding on infected dogs, coyotes, foxes, and wolves.
  • The larvae develop into an infective stage in the mosquito, and then mosquitoes can transmit the heartworm larvae to dogs and cats while they are taking a blood meal from the pet.
  • From there, the larvae go through several developmental stages as they mature into adult heartworms. The clinical course of disease is different between dogs and cats.
  • Dogs infected with heartworms typically have between 14 and 20 adult worms, although there can be more than 50! Cats usually have less than 6 adult worms (usually 1 or 2).
  • Worms living in a dog’s heart, lungs, and arteries will cause inflammation that can block blood vessels. Damage from a heartworm infection can be permanent.
  • Cats can develop a severe immune reaction from the migration of the larvae. This is known as heartworm associated respiratory disease (HARD).


Additional Resources:

​The American Heartworm Society (AHS) is an organization devoted to getting the word out about heartworm disease. The resources above were compiled from AHS information. Be sure to also check out their website for tons of great additional information!

The Companion Animal Parasite Council (CAPC) website is another informative resource.

~Author: Dr. C. Noureddine, DVM, MS