Understanding, Preventing and Treating Heartworms

Recently, fellow blogger Melissa Rice posted this piece about West Nile virus and how important it is to treat pets with products that repel and kill mosquitoes. That got me thinking about another mosquito-carried disease that is even more harmful to pets: heartworm. Here’s some interesting information on heartworm disease in general, and a series of questions and answers, based on the questions I frequently get from pet owners in my veterinary practice.

During the turn of the 19th Century, Thomas Jefferson became the 3rd President of our country. In true Virginian fashion, he wanted more land for our country and to find a waterway route from the east to the Pacific. Jefferson called a gentlemen, a long-time friend, Meriwether Lewis to put together and expedition to map and find this route. Captain Lewis was joined by William Clark, and together with a crew they formed the Corps of Discovery to embark on their historical journey.

Part of the group included Meriwether Lewis’s faithful companion, Seaman, a large Newfoundland dog. The Corps of Discovery faced a multitude of hardships along their journey which also included swarms of mosquitoes, as you can imagine, along waterways in the summer months.

So how does this bit of history relate to our pet care today? Though we don’t know if heartworm disease existed in the early 1800’s, we do know it exists today. Was Meriwether’s beloved Newfoundland exposed to heartworm disease from constant attack by the culprit of spreading the disease, the pesky mosquito? We will never know that answer either. But we still have mosquitoes and we definitely have heartworm disease currently. The bad news is that we can’t eradicate mosquitoes. The good news is we can prevent heartworm disease simply and effectively.

In this, Part I of my two-part series on heartworms, I will address questions on heartworm disease in general, primarily with regards to our dogs. In Part II, I will address the disease in cats.

So, what are heartworms?

As the name suggests they are a worm or parasite that lives in the heart, lungs and pulmonary vessels. The immature form are transmitted through a mosquito bite and migrate as they develop to the heart, where they can cause heart failure.

Are heartworms contagious?

Not in the direct sense. In other words, a heartworm-infected dog simply coming in close contact with another dog will not transmit the parasite. The infected dog would have to be “bitten” by a mosquito (part of the life cycle/development of heartworms occurs in the mosquito) and then the mosquito taking a blood meal from the non-infected dog. When the mosquito takes the blood meal from the dog, the immature heartworm is sort of vomited into the system of the now infected dog.

Are heartworms fatal?

 Unfortunately, the answer is YES. Left if your dog is unprotected, the numbers of heartworms are great enough or if your dog is already health compromised and left untreated, heartworm disease is fatal.

Do heartworms hurt?

There doesn’t seem to be any direct pain with the immature forms of the heartworms migrating. There also doesn’t seem to be any direct pain associated with the adult worms. However, heart failure and the symptoms this presents can be quite compromising and uncomfortable for your pet.

How can I tell if my dog has heartworms?

The unfortunate part of this is you may not know, unless tested, until it is too late to reverse the cardiac disease. However, a simple blood test that most veterinarians can do while you wait will diagnose heartworm positive cases. It is recommended that all dogs be tested at least annually (even if the dog is taking a preventative treatment). If you acquire a new dog and don’t know their heartworm status, have them tested. Young puppies (less than 5-6 months of age) probably will not be tested initially since the tests “look” for a specific portion of the female adult heartworm called an antigen, and to reach the adult stage of heartworm takes a minimum of months. Other symptoms you may see include: exercise intolerance, weight loss, chronic harsh coughing, gagging and an increased respiratory rate.

Can heartworms be treated?

Yes.  The health condition of your dog, the symptoms they are exhibiting and the stage of heart disease will determine the protocol for treatment. The treatment can be somewhat risky, especially if the worm burden is high and your dog is in compromised health. Treatment will occur in stages and your veterinarian will determine the best protocol to follow.

Can heartworm disease be prevented?

Hooray on this one!!! YES, YES, and YES.  There is no reason that a dog should be left unprotected.  There are a variety of great preventative products including oral (given once monthly), topical products and even injectable medications to protect your dog.

How often and when should my dog get or be on heartworm prevention?

Most topical and oral products are administered once monthly. Injectable preventions have much longer duration for prevention which can be up to a year with one injection. Your veterinarian will help you decide on the best option for you and your dog. Dogs should be on prevention year round with very few exceptions, pending the geographical area you live in. Even if you don’t have mosquitoes every month of the year, the added intestinal parasite protection is warranted.  Plus every year weather patterns change and mosquitoes may arrive earlier or be around longer than in other years. It is not worth the risk of leaving your pet unprotected!

Can people get heartworms?

Although we are exposed to the same heartworm-carrying mosquitoes as our dogs,  if we are exposed our immune system “fights off” the infection, so we are almost never affected by the disease. Our canine friends’ immune systems are not the same as ours, and therefore they are at risk.

Could heartworms come back after treatment?

If treatment is considered successful (negative testing after a period of a few months) and preventatives are given faithfully, the answer is no. They should not “come back”. However, prevention is key.

Bottom line: Don’t let your four legged “man’s best friend” go unprotected! There is no good reason for your dog to contract heartworm disease.  If Meriwether’s  brave Newfoundland were still around, today I am sure he would agree.


-Photo Credit: From flickr by Oliver Ruhm


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