What’s the Risk of Heartworm in my Dog?

What’s the Risk of Heartworm in my Dog?

In any discussion about keeping dogs healthy, one of the first topics to be raised will usually be heartworm. Around 250,000 dogs per year are diagnosed with heartworm, which puts your dog’s chances of getting this disease at about 1 in 200 (roughly the same as a person’s probability of getting diagnosed with cancer in any given year). Heartworm is particularly a cause of concern in dogs because virtually 100% of dogs who get exposed to the heartworm virus develop the infection, versus about 61% of cats (cats can also develop the disease). And once infected, the lifespan of heartworms (when untreated) in a dog is up to 7 years. Clearly heartworm presents an eminent risk, and it’s insidious enough and potentially deadly to warrant serious preventative treatment. Let’s learn more about what causes heartworm, your dog’s exposure to risk of heartworm, and the ways you can keep this common canine ailment at bay.

Where do heartworms come from?

Heartworm disease is caused by the heartworm organism, Dirofilaria immitis, which is a parasite; it is transferred to mammals such as dogs when bitten by mosquitoes, which serve as intermediary hosts. Microscopic agents of the parasite are transferred to dogs through the mosquito’s saliva, and there are about 70 different species of mosquito, which have been found to serve as carriers. Once an infected mosquito bites a dog, if the immune system of the dog does not destroy the parasite larva, the parasites will continue to grow and eventually reach the heart and pulmonary arteries of the dog, growing to adulthood in about six months. If the heartworms are untreated and allowed to reproduce inside the dog, they can multiply to numbers of up to 250 and severely inhibit heart function and blood flow. Only the bite of an infected host (mosquito) can infect a dog with heartworm; it is not directly transferable from one infected animal to another.

What factors increase risk of heartworm?

The number one factor that commonly increases risk of heartworm is climate and where you live: warmer, wetter, and more tropical areas naturally harbor more mosquitoes and so the risk of heartworm is greater. However, don’t think that because you live in a more dry or chilly climate, your dog is safe without preventative care — heartworm illness has been reported in all 50 states. The more time your dog spends outside, as well, the more likely he or she is to be exposed to mosquitoes carrying the virus; however, in a study on heartworm-infected cats conducted by North Carolina State University, 25% of them were solely indoor cats. Most heartworm infections have been diagnosed in medium to large breed, three to eight year old adult dogs. If your dog has been ill and his or her immune system has recently been compromised in any way, the risk of developing heartworm disease is increased.

What are heartworm symptoms in dogs?

Heartworm is difficult or impossible to detect in dogs until the parasites have been in the dog’s body for six to eight months, but if you’re not testing or treating your dog regularly for heartworm and he or she develops the following symptoms, see a vet:

  • Persistent cough
  • Lethargic, becoming easily winded
  • Lung whistling or other abnormal sound
  • Fainting
  • Fluid retention

How can heartworm be prevented?

Thankfully, with some diligence, heartworm is fairly easy to prevent in dogs, and you can keep your pet safe by administering a preventative medication once a month. These usually come in the form of chewable pills, but topical skin medications are available as well. Even during cooler months, it’s recommended that you continue treatment rather than stop and risk forgetting to start it up again once the weather gets warm. Many heartworm medications protect against other types of parasites, so year round treatment is also beneficial for that reason. And remember to get your dog tested for heartworm twice a year. Preventative steps to mitigate risk of heartworm are so important because once the disease is developed, it’s expensive to treat and hard on the animal. As with any medical treatment, it’s important that you consult with a licensed and knowledgeable professional before you begin a heartworm regimen for your dog.


We know your dog is a cherished member of your family, so our entire team shares a commitment to provide the best, most compassionate veterinary care for your dog. We offer a variety of dog services to in the Pflugerville/Austin-Round Rock, TX area including vaccinesdental careweight managementsenior care, and more. Call (512) 251-BARK today to learn more!