by Dr. Peter Dobias, DVM
Holistic look at the Heartworm prevention
A few days ago, one of my friends living in Vermont called me. She was wondering what I thought about heartworm prevention and if I could help her determine, if the monthly administration of heartworm preventive medication is really necessary.
The question threw me back in the 90’s, when the manufacturers of heartworm preventive drugs decided to take North America by storm. I remembered the drug reps visiting vet clinics on a regular basis telling us that it was only a matter of time and heartworm would widely spread in Canada. These visits were also accompanied by a subtle suggestion that selling the heartworm tests and preventive drugs could be a significant source of income for the practice.
As time progressed, the heartworm doom and gloom case scenario didn’t happen and that the risks of heartworm infection in my areas were clearly exaggerated.
On the basis of my findings, I made a decision not to recommend Heartworm preventive drugs in the area practice because the risk was practically zero and administering of any drugs is never optimal. In reality no one can be absolutely certain if down the road preventive medication doesn’t increase the tendency to chronic disease, organ failure or even cancer.
On the other hand, my friend’s situation is quite different because she lives in the Eastern US 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 of monthly prevention. To me, the monthly administration frequency seemed to be kind of peculiar because as far as I know, parasites do not carry an iPhone with a calendar and schedule.
I decided to bring clarity in the current situation to see what the frequency of heartworm preventive drugs really needed to be and also tell you more about the heartworm prevention alternatives that I use with my dog Skai. In order to do so, I need to give you answers to the following questions:
1. Heartworm incidence:
Heartworm life cycle is dependent on temperature that must remain above 57 degrees F (14 C ) for at least 45 days straight and at least 2 weeks of temperatures over 80 F ( 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, all year around 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 to administer heartworm medicine monthly, I urge you to learn more about the heartworm life cycle. The heartworm development goes through several stages before reaching maturity and it takes 2.5 to 4 months before the tiny stage of microfilaria leaves the muscles and starts settling in the pulmonary artery. When heartworm reaches its final destination of pulmonary artery near the heart, it takes about 3 – 4 months to reach maturity.
One doesn’t need to have a degree in math to figure that it takes somewhere between 5.5 to 8 months for microfilaria to mature into an adult worm and that your dog should be safe if you administer heartworm meds only once every 3 to 4 months if your live in the area where heartworm occurs.
So why would the drug companies recommend monthly heartworm prevention? The reason is clearly identified clearly in the study of Drs. Knight and Lok’s study on page 80 :
“…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 and life translation 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 ) is that drug companies can double or triple their revenues.
3. Safe alternative to heartworm preventive drugs
My dog Skai and I travel to Hawaii approximately twice a year for 2 months and I had to face the dilemma what to do about heartworm. I never felt totally comfortable about giving him any drugs because in my mind, there is no such thing as a little bit of poison.
Luckily, advances in heartworm testing offers DNA testing on the basis of PCR technology which allows me to test 3 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 manufacturers of heartworm meds. They are simply not needed if you follow this formula considering the duration of the heartworm seasons you can find out from the map on page 79
Number of Tests Required
(the last should be done at the end of HW Season)
Less than 4 months
4 – 8 months
8 – 12 months
Consider 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 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 World Wide Web.
Wishing you a happy, more informed heartworm season.
Dr. Peter Dobias, DVM
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