Thursday, April 2, 2015

What is Heartworm Disease?

Heartworm disease is a serious, potentially-fatal disease seen in pets in the United States as well as other parts of the world.  Heartworm disease is caused by heartworms (Dirofilaria immitis), which are parasites that can grow to be one foot long within an infected animal.  These parasites live in the heart and the blood vessels that carry blood from the heart to the lungs, and they can cause severe lung damage and heart failure.  In addition to dogs and cats, heartworms can live in other mammals, such as wolves, coyote, and foxes. These wild animals can serve as a source of infection for our pets.

The mosquito is essential in the transmission of heartworm.  Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microscopic immature worms called microfilaria which circulate in the bloodstream.  When a mosquito bites an infected animal and takes a blood meal, it picks up these microfilaria.  Over the course of 10-14 days, the microfilaria mature into an infective stage of larvae within the mosquito.  After maturation occurs, when that mosquito bites a dog, cat, or susceptible wild animal, the infective larvae are able to enter the new host.  Once inside the new host, it takes approximately six months for the larvae to mature into adult heartworms.  Adult heartworms can live for five to seven years in dogs and up to two to three years in cats.  The longer an animal is infected, the more likely it will show signs of disease.  The signs of heartworm disease can vary in dogs and cats but often relate to damage to the heart and/or lungs.  These signs can be as subtle as a loss of appetite, or as severe as sudden death.  We will discuss the signs in more detail in a future post. 

Heartworms are present in all 50 states, and the American Heartworm Society estimates that over one million dogs in the United States are currently infected with adult heartworms.  Because infected mosquitoes can get inside your home, both indoor and outdoor pets are at risk.  Prevention is the key to keeping your pet healthy and safe from heartworm disease.  A variety of safe and effective preventives are available for both dogs and cats.  Look for more blog posts later this month written by our staff members to learn more about heartworm disease and what we recommend to prevent it, or call our office at (203) 775-3679 for more information.

By Michael Dattner, DVM

Michael Dattner, DVM, along with his wife, Silke Bogart, DVM is the owner of Brookfield Animal Hospital.  Please click here  to read his complete bio. 



  1. that is great thing to do. i am in love with this page Lost and found

  2. It is great to know more about heart worms. Things like this are so important for pet owners to be aware of. The sooner something is detected and treated the better.

  3. More people need to know what it is that heartworm disease is. That way they can tell what the signs are when their pets have it and what they can do to take care of it. People need to be taking their pets into animal hospitals more often to get taken care of.