An Hoang Veterinary Student Texas A&M University College of Veterinary Medicine

Canine Heartworms and Heartworm Disease

What are Heartworms? A parasitic worm that lives in the right side of the heart of Dogs and Cats Photos from:

A day in the life of a Heartworm – Life Cycles - A life cycle describes the different stages in the life of an organism, including what other organisms it needs to live, and how it reproduces.

Life Cycle of Heartworms Life Cycle from The microfilaria grow up to be adult heartworms and produce more microfilaria that will be pumped out into the blood stream and be picked up during a mosquito bite! The microfilaria in the mosquito’s saliva are transmitted to the dog when the mosquito bites the dog Baby heartworms – “microfilaria” are found in the salivary glands of mosquitoes Over a 5 month period the microfilaria will move through the dogs body and make themselves at home in the right side of the heart and the blood vessels that go to the lungs!

Where do Heartworms Live?

We take a small blood sample, mix a few drops of blood with special chemicals and pour the sample on a “snap test”. The test detects proteins produced by adult heartworms. Your dog’s veterinarian will usually do this test on your dog during his yearly check up. Heartworm Testing: How do we know our dogs have Heartworms? Photo from:

Heartworms –what do they look like? Microfilaria circulate in the blood of dogs – if we take a sample of blood and put it on a microscope slide we can see the microfilaria. Photo from:

Heartworm Infection vs. Disease Infection: The presence of heartworms (immature or adult) is detected but there are no clinical symptoms, i.e. the animal does not appear “sick”. Disease: When the presence and numbers of heartworms impedes the physical well being of the animal causing clinical symptoms such as, coughing, vomiting, nose bleeding, exercise intolerance, heart failure, heart enlargement

The Heart

Heartworms and the Heart When Heartworms are mature adults, they live in the Right side of the heart and the pulmonary arteries. Presence of the worms blocks blood flow and impedes the heart’s ability to pump blood to the lungs and body

Heartworms can also affect the lungs When the worms die, they worm or pieces of worms shoot off through the vessels to the lungs. The vessels of the lungs are very small and the worm or piece of worm can block the vessel – this makes it more difficult for blood to reach parts of the lung or stops blood flow completely  Author of illustration: Patrick J. Lynch, medical illustrator Heartworms and the Lungs

Heartworm Disease Ultimately the heart gets so tired from pumping it tires out becomes very weak – we call this heart failure The lungs produce fluid to try to “wash” the lungs clean - but unfortunately, fluid in the lungs makes it hard for the dog to breathe With the heart and lungs not working well, the dog gets very sick

Heartworm Treatment If a dog has a positive heartworm test, it’s important to treat the dogs before the problem gets worse. The dog will get two injections about a month apart. During treatment time it’s important the dog remain as quiet as possible to risk complications.

Heartworm Prevention Heartworm infection and disease is easily prevented with monthly drug treatments.

Any Questions?

The End!