Understanding Heartworm Disease

I’ve heard and seen some things lately about heartworms, and I realized that while I have a general understanding of the disease, there was still a lot I didn’t know. So, I thought I would share this important information, which can save your dog’s life!

What is Heartworm Disease:

Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living  in the arteries of the lungs and occasionally in the right side of the heart of dogs, cats and other  species of mammals, including wolves, foxes, ferrets, sea lions and (in rare instances) humans.  Dogs and cats  of any age or breed are susceptible to infection. Heartworms are transmitted by mosquitoes, and cannot be caught from an infected animal. However, when a mosquito bites an infected animal, and then bites a healthy animal….the cycle begins!


Symptoms of Heartworm disease:

For both dogs and cats, clinical signs of heartworm disease may not be recognized in the early stages, as the number of heartworms in an animal tends to accumulate gradually over a period of months and sometimes years and after repeated mosquito bites. Recently infected dogs may exhibit no signs of the disease, while heavily infected dogs may eventually show clinical signs, including a mild, persistent cough, reluctance to move or exercise, fatigue after only moderate exercise, reduced appetite and weight loss. It is SO important to understand that many dogs do NOT show symptoms of this disease until the late stages of the infection!

Testing for Heartworms:

An annual blood test, done by a veterinarian, is recommended. This will check to be sure that your dog has not been infested with the disease. Heartworms need to be detected as soon as possible before irreversible heart and lung damage occur. Early detection and treatment are always best!


There are two drugs that are FDA-approved and commonly used for heartworm treatment. Those are Caparsolate and Immiticide. Both contain arsenic.

  • Caparsolate is given intravenously twice a day for two days. Caparsolate does not always kill all the worms. Immature worms, especially females, are relatively resistant. Treatment with Caparsolate must be followed by treatment for microfilaria. The drug is not safe to use on high-risk dogs with congestive heart failure, liver failure, or kidney impairment.
  • Immiticide eliminates more than 90 percent of worms, making it more effective than Caparsolate. It has a higher margin of safety and can be given to dogs at high risk. Immiticide is given by intramuscular injection once a day for two days. If the dog is severely debilitated by heartworms, the drug can be given in divided doses 30 days apart.

After treatment, the worms begin to die. And as they die, they break up into pieces, which can cause a blockage of the pulmonary vessels and cause death. That’s why dogs have to be kept quiet during the treatment and then for several weeks afterward. Studies have shown that most of the dogs that die after heartworm treatment do so because the owners let them exercise. It’s not due to the drug itself.

Treatment Complications:

 With Caparsolate, significant toxic reactions can occur, and include loss of appetite, vomiting, diarrhea, jaundice, kidney failure, and death.

Pulmonary Thromboembolism-Dogs that are not kept quiet and cool for approximately a month after the  initial injection of heartworm medicine or who have a heavy infestation of  heartworms generally experience some degree of pulmonary thromboembolism.  Symptoms of this include fever, coughing, and the coughing up of blood.

So, not only is the disease extremely harmful, but the treatment itself is hard on the dog. Take our sweet little Hope for example. She is a young, energetic pup that LOVES people and dogs! However, because of having to go through heartworm treatment, she has had to be restricted and kept quiet. She can’t play with the other dogs; she can’t get all excited for her humans. Just that part alone is hard on her, let alone having these nasty worms inside her heart.

Hope is coming to the end of her recovery, and is doing well. Now is ready to find her forever family!
Hope is coming to the end of her recovery, and is doing well. Now she is ready to find her forever family!

Some important facts:

  • It’s perfectly acceptable to adopt a dog with heartworms, but you have to be dedicated to having the disease treated appropriately, because it’s a horrible disease that can lead to a dog’s death if left untreated.
  • A dog can NOT outgrow this disease. You must seek treatment!
  • Dogs can get heartworms multiple times throughout a lifespan, if they are not on a monthly preventative.
  • A dog can/should live a perfectly happy, healthy life after treatment! As long as you keep them on the monthly preventative, they should never have complications or get heartworms again!

Here’s a great short video on the life of a heartworm: http://youtu.be/FKKU0CzDWWw

Informational websites:

American Heartworm Society: http://www.heartwormsociety.org/pet-owner-resources/heartworm.html

ASPCA: http://www.aspca.org/pet-care/dog-care/heartworm

Pet WebMD: http://pets.webmd.com/dogs/guide/heartworms-in-dogs-facts-and-myths?page=2

I hope this information has been helpful, and will remind everyone how important the preventative medication is!

Have a wonderful weekend!!


5 thoughts on “Understanding Heartworm Disease”

  1. GREAT info! Thanks so much! I did some house-sitting once for friends with TWO dogs both on heart worm treatment, and it is really difficult on dogs and owners to treat HW. Taking the once-a-month preventative is waaaaaay easier…

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