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Are drug companies honest about heartworm?

Are drug companies honest about heartworm?

Holistic look at heartworm prevention

A few days ago, one of my friends living in Vermont called me. She was wondering what I thought about heartworm prevention. She asked me to help her determine if the monthly administration of heartworm preventive medication is really necessary. The question threw me back to the 90s when heartworm prevention drug manufacturers decided to take North America by storm. I remember the drug reps visiting vet clinics on a regular basis telling us that it was only a matter of time and heartworm would be widespread in Canada. These visits were also accompanied by a subtle suggestion that selling heartworm tests and preventive drugs could be a significant source of income for the practice.

As time progressed, the heartworm doom and gloom scenario didn’t happen and the risk of heartworm infection in my area was clearly exaggerated.

Heartworm case map Canada

On the basis of my findings, I made the decision not to recommend heartworm preventive drugs in the area of my practice because the risk was practically zero and administering any drugs is never optimal. In reality, no one can be absolutely certain if preventive medication doesn’t increase the tendency to chronic disease, organ failure or even cancer down the road.

On the other hand, my friend’s situation is quite different because she lives in the eastern U.S., where heartworm is a real possibility. I saw her question as a great opportunity for me to review the lifecycle of heartworm once again to see if drug companies were honest about their recommendations for monthly prevention. To me, the monthly administration seemed to be kind of peculiar because, as far as I know, parasites do not carry an iPhone with a calendar and schedule.

Heartworm case map USA

I decided to bring clarity to the current situation to see what frequency is needed for heartworm preventive drugs and also tell you more about the heartworm prevention alternatives that I used with Skai and now use for Pax. In order to do so, I need to give you answers to the following questions:

  1. What is the risk of heartworm disease in your area?

  2. What is the minimal frequency of administering preventive drugs?

  3. Are there any alternatives?

1. Heartworm incidence

The life cycle of heartworm is dependent on a temperature that remains above 57F (14C) for at least 45 days straight and at least two weeks of temperatures over 80F (26C). If these conditions are not fulfilled, the parasite cycle cannot be completed and your dog is safe.

Based on the recommendations of Dr. David Knight and Dr. James Lok from the American Heartworm society, even with the most cautious conventional medical protocols, a year-round heartworm preventive schedule is exaggerated with the exception of Florida, some parts of Texas and Hawaii. According to their conventional opinion, preventive treatment is unnecessary in the winter months and definitely doesn’t need to be started before or after the months noted on the map in their paper.

2. Heartworm life cycle

Before you succumb to the marketing pressure and fear and administer heartworm medicine monthly, I urge you to learn more about the heartworm life cycle. Heartworm development goes through several stages before reaching maturity and it takes two-and-a-half to four months before the tiny stage of microfilaria leaves the muscles and starts settling in the pulmonary artery. When heartworm reaches its final destination in the pulmonary artery near the heart, it takes about three to four months to reach maturity.

One doesn’t need to have a degree in math to figure that it takes somewhere between five-and-a-half to eight months for microfilaria to mature into an adult worm and that your dog should be safe if you administer heartworm meds only once every three to four months if you live in an area where heartworm occurs.

So why would the drug companies recommend monthly heartworm prevention? The reason is clearly identified in Drs. Knight and Lok’s study:

“…given what is presently known, continued adherence to a policy of superfluous chemoprophylaxis is disquieting because financial expediency for the veterinarian conflicts with clinical objectivity and client consent is predicated on unrealistic expectations. Clients mistakenly believe that they are purchasing additional protection for their pets, but in reality they are not. If the truth was known to them, few clients would agree to unnecessarily double their expense for heartworm prevention.”

In real language, most vets are too busy to question the recommendations that drug companies give them about heartworm prevention. I strongly believe that the main reason for over recommending heartworm prevention (chemoprophylaxis) dose frequency is that drug companies can double or triple their revenues.

3. Safe alternative to heartworm preventive drugs

 I travelled with Skai and now take Pax to Hawaii approximately twice a year for two months and I had to face the dilemma of what to do about heartworm. I never felt totally comfortable about giving any drugs because, in my mind, there is no such thing as a little bit of poison.

Luckily, advances in heartworm testing brought about DNA testing on the basis of PCR technology, which allows me to test multiple times a year for any presence of heartworm. This test has virtually no false negatives, which is great news for your dog.

I can see that these tests are  a serious threat to the hefty profits of heartworm meds manufacturers because they are simply not needed if you follow this formula. The duration of the heartworm season can be found on the map on page 79 of the study.

Season Duration   Number of Tests Required
    (The last should be done at the end of the heartworm season)
Less than four months 1 test
Four – eight months 2 tests
Eight – 12 months 3 tests

Considering the facts above, in order to prevent heartworm and keep your dog safe, all you need to do is test your dog if you live in an affected area. If the results are positive (heartworm DNA is present) make sure that you consult your veterinarian before administering any heartworm meds. Heartworm preventive medication can be used only if adult heartworms are NOT present because using preventive drugs on adult heartworm can cause serious problems and a different treatment protocol must be used.


I regret to say that similar to the vaccination scam, monthly heartworm prevention is yet another dishonest marketing plot. What I am confused about is why drug companies continuously try to trick us and frighten us, instead of making a living the honest way. No matter what they are planning to try next, I believe that eventually, they will have to become more honest in order to survive because it is much more difficult to hide the truth in the age of worldwide web.

Wishing you a happy, more informed heartworm season.

© Dr. Peter Dobias, DVM

About the author

Dr. Peter Dobias, DVM is an Integrative veterinarian, nutritionist and creator of natural supplements for dogs and people. Helping you and your dog prevent disease, treat nutritional deficiencies, and enjoy happier, healthier, and longer lives together.

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