What is heartworm disease?
Heartworm (Dirofilaria immitis) is a mosquito-borne parasite that causes heart, lung and vascular disease in dogs and cats. Infected mosquitoes inject immature heartworms (microfilariae) under the skin during a bite. The immature worms grow gradually to adult size as they travel from the site of the bite towards the heart. Six to seven months later, fully mature, adult worms can be found inside the heart and pulmonary arteries.
The worm burden causes progressive tissue damage and blood-flow obstruction that eventually results in death from cardio-vascular complications.What are the symptoms of heartworm disease?

  • Pets in the early stages of disease may have no symptoms.
  • Symptoms appear and gradually worsen as heartworm disease progresses.
  • They may include:
    • Coughing
    • Fatigue
    • Difficulty breathing
    • Exercise intolerance
    • Poor appetite
    • Weight loss
    • Abdominal distension

What pets are at risk for heartworm disease?
Any dog or cat bitten by an infected mosquito can get heartworm. Mosquito prone areas have the highest rates for the disease.


How is heartworm disease prevented?

  • Heartworm disease is prevented by consistent and continuous use of preventative medications along with yearly heartworm testing.
  • Heartworm preventatives work by killing immature worms before they can reach adulthood.
  • They DO NOT kill adult heartworms and must NOT be given to dogs with possible adult-heartworm infection.
  • Preventatives are available by prescription only in oral, topical or injectable formulations.
  • Popular preventative brands include: HeartGuard ®, Interceptor ®, Sentinel®, Revolution®, Trifexis® and Advantage Multi®.
  • Puppies should be started on heartworm medications by 6-8 weeks of age.
  • Heartworm testing is required prior to starting a preventative in dogs older than 7 months of age.

What is a heartworm test? Why is it required in dogs?

  • A heartworm test allows detection of adult worms in the dog’s heart.
  • It’s important for two reasons:
  • First, adult worms are not killed by standard preventative meds; dogs with adult worms will progress to heartworm disease despite preventatives.
  • Second, adult worms can flood the bloodstream with large numbers of immature worms (microfilariae) that are killed by preventives. Killing these suddenly with a preventative can trigger shock and sudden death.
  • Annual heartworm testing helps avoid both of these potential complications.

What if my dog tests positive for heartworm?

  • The first step is to repeat the test to confirm the results.
  • If the repeat test is also positive you will need to consult your veterinarian for a treatment plan.
  • Adult heartworms require adult-specific (adulticide) medications that require close veterinary supervision.