Or, why does my dog need heartworm pills every month?

I've said it many times before, and it bears repeating again.  If you choose to do nothing else for your dog, heartworm prevention is still an absolute necessity.  Now, I obviously don't recommend skipping vaccinations, flea control, or otherwise neglecting care for your dog.  But heartworm disease is a killer, and absolutely preventable for a fraction of the cost and risk of treating it later.

What is heartworm disease?

Heartworm disease is caused by a parasitic worm called Dirofilaria immitis.  The parasite attaches to the inside of the blood vessels near the heart and grows to about the size of a spaghetti noodle.  Disease can be caused by as little as a single worm, but there are often many of these worms present in affected dogs.  The presence of heartworms in these vessels causes damage to the heart, blood vessels, and lungs over time, and eventually leads to heart and lung failure and death.


Heartworm disease and your dog (or cat!)

How do dogs get this disease?
Heartworms in a dog mate and reproduce in the blood vessels where they live.  Thier offspring, called microfilaria, are microscopic baby worms that freely circulate through a dog's bloodstream.  When an infected dog is bitten by a mosquito, these baby worms are ingested with the mosquito's blood meal.  They spend a few weeks living it up in the mosquito, where they grow a bit and eventually move to the mosquito's salivary glands, ready for deployment.  The infested mosquito then bites another dog, and the baby worms are injected out of the salivary glands and into the dog's bloodstream, ready to mature and begin the cycle anew.

Living in central Florida, there is no time of the year when mosquitoes aren't a problem.  Sure, they're less active in what we call "winter", but with 72 degree weather in January, they can still wreak havoc!  While some folks in other parts of the country may get away with skipping prevention for part of the year, that's not an option here.  Heartworm disease is endemic in this area, meaning it is present 'in the wild' all the time.

​But my dog is inside all the time!  She only uses pee pads!
Mosquitoes are more than happy to come into your home to feed.  The mosquitoes around my house insist on it.  And when they come in, they'll bring heartworms with them!  While Fifi may have less exposure, staying inside all the time does not eliminate the possibility of contracting heartworm disease.

How can I tell if my dog has heartworms?
In the early stages of heartworm disease, there is no visible sign of the disease.  Being the well adapted parasites they are, heartworms have developed mechanisms to live inside dogs for a long time without killing them.  After all, if they killed dogs immediately, they wouldn't have time to breed and spread to new hosts.  A dog may have worms inside for months or years without showing any signs of disease.  However, when signs occur, it indicates that a large amount of damage has already taken place.

Over time, irritation to the heart and vessels causes the heart to enlarge and the vessels to become thickened and less elastic than normal.  The worms also cause irritation in the lungs, which causes a condition similar to emphysema.  Dogs have an ability to compensate for this damage until it gets pretty bad, and when they finally show signs it is bad news for your pet.

The first signs pet owners usually notice are dry coughing and wheezing.  This indicates that your dog's lungs are in bad shape.  Next, you may notice swelling in your dog's belly or a wet cough.  These are signs that the heart is no longer functioning efficiently, and allowing fluid to accumulate.  Obviously, these are things we would all like to avoid!

Fortunately, we can detect heartworms within a few months after infection, before any physical signs are present.  We use a simple test on a single drop of blood, which detects molecules produced by the female worms.  This allows us to treat heartworm cases before they become life threatening.

So you can treat the disease?
Yes, we can, but at a great cost.  Not only is the treatment expensive ($800-$1200), it requires use of medication that is basically poisonous to your dog as well as the parasites.  The treatment is dangerous, and your pet will have to be kept in a kennel for a couple months after treatment to prevent further serious damage to the lungs after the worms die.  Despite our best care, a small number of dogs will have an adverse reaction to treatment, which can be fatal.  This is usually not the case, and the vast majority of patients recover without complication, but why would we want to take that chance?  Also, there is inevitably some damage done to the heart and lungs before any signs are seen, so prevention is the best option!

What about my cat?
While most people don't realize it, cats can actually get the same parasite as dogs.  However, cats don't tolerate the parasite nearly as well as dogs do.  This is due to the fact that the heartworm is specially adapted to deal with the chemistry and immune response in dogs.  In short, this means that while it is harder for heartworms to survive to adulthood in cats than dogs, they can be especially bad if they do.  Often, the only outward sign we see when a cat contracts heartworm disease is sudden death when the worm dies.  

What can I do to prevent this?
Prevention of heartworm disease is simple.  First, we will do a yearly blood test to make sure your pet has not picked up heartworms.  Then, you will prevent heartworms from infecting your dog by simply giving them a medicated treat once a month.  We recommend Trifexis™ for the gold standard in flea and heartworm protection for dogs in a single pill.  We recommend Revolution™ for monthly prevention of fleas and heartworm for your feline friends.

That's it.  That's all you have to do to prevent this deadly menace!

More information can be found at:   The American Heartworm Society

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