Most dog owners have likely heard of heartworm disease but may not know how it is transmitted and how important prevention is. Heartworm is spread by mosquitoes; and we have plenty of them in Northern Minnesota. Heartworm disease affects dogs, cats, and ferrets, but heartworms can also live inside other canines including wolves, coyotes, and fox. This disease is serious and potentially fatal, but easily preventable.


Mosquitoes are essential to heartworm transmission as the intermediate host for the microscopic worms called microfilariae (“baby heartworms”). The microfilariae circulate in an infected canine’s bloodstream. The mosquito bites the infected dog and ingests the microfilariae which develop into larvae inside the mosquito over 10-14 days. The mosquito then bites another canine and deposits the microfilaria in the new host where they travel to the heart and develop into adult heartworms over about 6 months.

Picture Credit: American Heartworm Society


Patients in early stages of heartworm disease may not exhibit any symptoms. This allows for easy transmission from dog to dog before diagnosis and treatment. As the disease progresses, pets may develop heart failure. Symptoms may include:

  • Cough
  • Exercise intolerance
  • Decreased appetite
  • Weight loss
  • Swollen abdomen
  • Labored breathing
  • Pale gums


Picture Credit: Idexx.com

The veterinary community recommends screening for heartworm disease once a year. In our area tick diseases are also very prevalent, so the Idexx 4Dx snap test is commonly used.  It tests for the presence of antibodies of heartworm and three common tick diseases: Lyme disease, Ehrlichiosis, and Anaplasmosis. More testing may be recommended after a positive test to confirm and stage the disease.


There are many theories on treatment for heartworm disease. Any of them should be done with caution and under supervision of your pet’s veterinarian. Prior to treatment blood work, radiographs and specific tests will be recommended to determine the stage of the disease. Supportive care, exercise restrictions, and additional medications may be needed for more severe cases. The current recommendation from the American Heartworm Society is a multiple step process with a strict regimen of medications and injections. Antibiotics are given to prevent complicating factors from secondary bacteria. The medication to kill the adult heartworms is injected deep into the dog’s muscle. This can be painful, and there is risk of negative side effects. Treatment should be done even if the patient is asymptomatic.


“An ounce of prevention is worth a pound of cure.”

Benjamin Franklin

Mr. Franklin could not have been more correct, especially when it comes to Heartworm disease. The oral monthly preventives work by killing any microfilariae that have been injected into the dog in the past 30 days. Therefore, we recommend starting it in the spring, a month after the mosquitoes are first seen, if you’re not giving it year-round. According to the American Animal Hospital Association, heartworm preventive costs on average $10-15 per month. Treatment on the other hand can be well over $1,000. Drug companies have also made it easy for clients to give their pets heartworm preventive with tasty, chewable, treat-like products. Most also treat for hookworms, roundworms, and some for tapeworms. With so many options available it can be overwhelming, veterinary professionals can answer your questions and make recommendations.

Heartworm disease is a widespread problem; it has been diagnosed in dogs in all 50 states. Even after treatment there can be long-term effects that can shorten your dog’s life. Save your dog the pain and risk and give them a tasty, once monthly treat. It will benefit for you and your canine friend in the long run.