Neuse River Golden Retiever Rescue
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Neuse River Golden Retiever Rescue

A foster dog and HEARTworm Disease

by User Not Found | Sep 16, 2014

It has been far too long since I climbed on top of my heartworm shaped soap box.  The timing of this after our recent discussion about heart murmurs is actually great but the reason for it is sad. 

Meet one of our current foster dogs.

He was never given heartworm prevention and to no surprise, he now has heartworm disease.  The frustrating and absolutely sickening part about it is, he is only two years old and his disease is so bad he has been put on medication to help his heart function normally. 

Let’s revisit heartworm lifecycle for just a moment.  A mosquito feeds on an infected animal and ingests what’s called microfilaria.  Microfilaria mature in the mosquito for about two weeks and then are passed in to another animal by the mosquito during a bite.  Typically this is where your heartworm prevention would kick in to “deworm” and get rid of this infective larva stage.  No prevention? Then this larva makes its way thru the blood for about 1 to 3 days and eventually migrates in to the tissue.  Once in the tissue, they grow up in to horrid teenage worms in about 50-70 days.  At this point, they make their way to the heart and lungs where they develop in to full adults and start making microfilaria.  If you have done some simple math here, heartworms actually can’t show up in a dog until they are about 6-7 months old because of this complex life cycle.  So let’s go back to our foster dog.  He is only two years old, so we would like to assume that because of his age and the length of the heartworm life cycle, that his worm burden would be low.  For the past several weeks, his foster has reported lots of coughing, so much that it’s even keeping everyone up at night.  Although this is common with our dogs with heartworm disease, it continued to be a major problem for him.  This past week, we sent our little buddy back to the vet for a more thorough once over to make sure that nothing else was going on.  First, an exam.  Our vet heard a grade 2 heart murmur (which was present when we bought this guy in) and he also said the heart and lung sounds were muffled.  This usually means that something, like fluid, is obstructing the heart or lungs and is making it hard to hear.  So we took an x-ray.  Now you can’t see heartworms on an x-ray, but what you can see is the shape and pattern of a heartworm infection.  To explain what I mean, let’s play with pictures.  Remember that I am a scientist, not an artist.HD Blog Pic#1

This is a simple depiction of a heart.  Blood comes in from the body (blue and deoxygenated) and enters the right side (atrium), is pumped thru (ventricle) and in to the lungs.  From the lungs it gathers oxygen and comes back to the heart (left atrium to ventricle) and is pumped out in to the body.  Heartworms come from the body tissues, so they enter the right side of the heart first and actually swim there to maintain position.  As they die, they get pushed in to the lungs via the pulmonary artery.  Once the heartworms are in the lungs, there is no exit, so they must remain there until the body’s cells can chew them up and digest them.  Heartworms are about the size of a spaghetti noddle and your cells are microscopic, so you can imagine about how long this takes.  During this time, your dog is at constant risk for what is called a pulmonary embolism (PE) where the worms can block the pulmonary artery and cause difficulty breathing, collapse, rapid heart rate, chest pain, shortness of breath, cyanosis (‘turn blue’), and sudden death.

As long as your dog is not on heartworm prevention, they can always get heartworm disease, even if they have had it before and been treated for it.  Without prevention, they can get infected by mosquito bites over and over and over again sending more and more heartworms to the heart.  As adults, heartworms can live 2-5 years in a dog and that’s enough time for them to start piling up.  After all, heartworms have no natural enemies inside the body.  A dog with heartworm disease can have anywhere from 2 to hundreds of worms at 4 to 12 inches long.   It’s parasitic genius.  Here is where the problems are just beginning for our dogs.  Let’s look at this picture again, only this time, I’ve labeled the valves in the heart.  We recently talked about their job between chambers of the heart, to keep the blood from back-flow and to seal off the chambers as the heart pumps blood where it needs to go. 
HD Blog Pic#2

As worms begin to fill the chambers of the heart, they can jam up these valves, causing them to leak blood and causing a heart murmur.  When the heart’s ability to pump blood to the lungs for oxygen and back out to the body to nourish organs is compromised, there is no backup!  It must only work harder to make that happen and is driven by signals from the organs.  Like trying to pack everything in your carry-on luggage to avoid bag fees, worms start to get packed in too tightly that they get pushed into the arteries and lungs and sometimes back out in to the body.   And here is that famous model you see at your vet’s office, the heart in the jar overflowing with worms that are wriggling out of all kinds of spaces.  It is meant to scare you and it should, but now you know it is not an exaggeration. 

Now that we know what is happening in severe heartworm disease, let’s go back to our little foster guy.  His x-ray showed what we expect, typical “right-sided” heart enlargement.  No surprise there since we know that heartworms live in the right side of the heart.  But, we also saw a lot of blurry lines in and around his lungs, which means that there is probably fluid obstructing the picture on x-ray.  This is known as pulmonary edema or fluid build-up in the lungs.  Because this poor pup has so many worms obstructing the valves and pumping of blood thru the heart, his heart has to work harder.  Working harder means more pressure inside those chambers.  More pressure means pushing the blood that is pumped in to the lungs in to the air sacs inside the lungs.  This fluid build-up will spread to other parts of the body and with the increased pressure in his heart, it will eventually fail.   Thanks to an ECHO we could assess where the worms are and the medications we can safely use to help his heart not have to work so hard.  He will be rechecked in a week to determine if he can continue heartworm treatment.  The longer the worms are present, the more damage is done to the heart and lungs so treatment is a must.  There is no way for us to medically manage him with the supposed “slow kill” method because heartworms can live for several years, his heart would fail long before the worms die, even with medication.  His heart looks something like this
HD Blog Pic#3

My moral of the story, please, please, please give your dog heartworm prevention.  Every dog, every month because this is a 100% PREVENTABLE disease.  Heartworm prevention costs you about the same as one latte a month, so there are no excuses.

Please send good juju to our little pup as we work hard to help him thru this horrible situation.  I promise to update you and let you know how he’s doing!

After three months of treatment and a year long effort, Baelfire has finally beaten heartworm. However, because the damage to his heart was too severe for repair, he will remain on medication to help his heart function normally for the rest of his life. NRGRR and his loving fosters will take care of him and make sure that he gets everything that he needs. His medication is expensive and sadly this all could have been prevented with an inexpensive monthly Heartworm preventative. Please educate yourself on this terrible disease and make sure your dog gets preventative!  Every dog, every month!  Many thanks to all who have helped Bael along the way. And kudos to one of his fosters for getting these great photos recently of a happy and heartworm free Baelfire!
Bael 2016
Bael2 2016

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