Heart to Heart: The Importance of Heartworm Prevention

Heartworm PreventionMost of us are aware that mosquitoes can spread dangerous diseases to humans, but did you know they can also transmit a deadly illness to our pets called heartworm disease?

Heartworm disease is a severe and potentially fatal condition affecting a pet’s heart and lungs. It can be found in all 50 states and in Canada; infecting cats, dogs, and many other wild species. Over 30 species of mosquito are known to transmit the disease. With spring in the air, the team at Wellesley Natick Veterinary Hospital wants to review the importance of heartworm prevention.

How is Heartworm Transmitted?

The heartworm life cycle is long and complex and requires two host animals to complete. In summary:

  • A mosquito bites and takes a blood meal from an infected animal.
  • The baby heartworm larvae, or microfilariae, develop in the mosquito’s body for 10-30 days.
  • The mosquito bites a different host, depositing the microfilariae on the skin. From there, they enter the bloodstream where they circulate for several weeks. Eventually, they make their way to the heart and pulmonary arteries, where they mature into foot-long, adult heartworms capable of reproduction.
  • The adult heartworms release new microfilariae back into the bloodstream, where they can once again be picked up by a mosquito and spread to other unsuspecting hosts.

Adult heartworms live 5-7 years in dogs and 2-3 years in cats. They can infect any breed, age, shape, or size of pet.

Signs and Symptoms

Signs of heartworm may be subtle and can look like symptoms for other diseases, as well. In the early stages, dogs may show no symptoms at all, which is why regular heartworm testing is vital for early diagnosis. As the infection progresses, signs become more apparent. This can include:

  • Exercise intolerance
  • Sudden onset cough
  • Lethargy
  • Inappetance
  • Weight loss
  • Breathing difficulty
  • Abnormal sounds in the lungs
  • Collapse
  • Sudden death


Diagnosing heartworm hinges on having an accurate and complete history of your pet’s lifestyle, as well as a physical exam and certain diagnostic tests, including:

  • Blood antigen test
  • Blood antibody test
  • Chest x-rays
  • Cardiac ultrasound or echocardiogram

We may also recommend testing to determine the effects of the disease to provide needed support and therapy.


For dogs, treatment involves injections that kill the adult heartworms. Because dead and dying worms can cause blockages in your pet’s pulmonary arteries, there’s always a serious risk to treatment; your pet may need to be hospitalized for observation. Exercise is also restricted for the duration of treatment (often several weeks), so as not to exacerbate these complications.

Unfortunately, there’s no approved drug for treating heartworm in cats. Typically, symptoms are treated with the hope the cat outlives the worms. However, a respiratory emergency or even sudden death can be the result of a cat’s lungs reacting to the dead and dying worms inside.

Heartworm Prevention

The best news about heartworm is that it’s easily preventable with year round protection.

In addition to monthly topical or chewable preventives, there’s now an injectable heartworm medication for dogs called Proheart 6, which can be given in our office every 6 months. This frees you from having to remember your pet’s monthly dose, and it’s been 100% effective in clinical trials. This is a convenient option that can easily coincide with your pet’s wellness visit.

We hope this overview about the importance of heartworm prevention is helpful. If you have any questions or would like more information, please don’t hesitate to give us a call.