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: http://www.merckvetmanual.com/
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
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!
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!
The microfilaria in
the mosquito’s
saliva are
transmitted to
the dog when
the mosquito
bites the dog
Life Cycle from http://www.stopwormsdead.co.uk/
Where do Heartworms Live?
Heartworm Testing: How do we know our dogs
have Heartworms?
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.
Photo from: http://www.vmth.ucdavis.edu/Cardio/cases/case27/tests.htm
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: http://www.stanford.edu/class/humbio103/ParaSites2006/Dirofilariasis/Diagnosis.htm
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 and the Lungs


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
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!