In a previous post, I mentioned that folks are giving monthly doses of insecticide to their dogs to prevent heartworm, but that an every-other month dose in warm weather will do just as well, and that your dog does not need to be dosed at all during cool weather (night time temperatures of under 57 degrees).
I have, of course, written about all this before and I encourage folks to go read that now.
None of this is new, of course. In fact, it was spelled out in a 1998 article by David H. Knight, DVM and James B. Lok, PhD. published in Clinical Techniques in Small Animal Practice and entitled Seasonality of Heartworm Infection and Implications for Chemoprophylaxis. As Knight and Lok note in that paper:
The practice of some veterinanans to continuously prescribe monthly chemoprophylaxis exaggerates the actual risk of heartworm transmission in most parts of the country and unnecessarily increases the cost of protection to their clients.
The authors go on to say, in a nice under-stated way, that heartworm hysteria pays a nice dividend for vets.
There is also a tremendous financial incentive to veterinarians to promote heartworm chemoprophylaxis because they control distribution of these excellent products in a market that is already large but not yet saturated. Unfortunately, preoccupation with worse case scenarios imparted by the profession to our client's and what could be perceived as an obvious economic self interest for veterinarians to promote chemoprophylaxis has encouraged an insidious overuse of a good thing. The well-intentioned promotion of heartworm awareness and prevention may overshadow the fact that in the temperate latitudes, heartworm transmission is seasonal and chemoprophylaxis is not necessary on a continual basis.
Knight and Lok note that vets hide the truth from their clients because it is in their financial interests to do so.
[W]hat harm is there in liberally dispensing these drugs? The issue that needs to be considered is whether medical justification should prevail over entrepreneurial interests in dispensing drugs intended to prevent rather than cure disease? Because veterinarians are permitted to sell the drugs they prescribe, use may not always be based strictly on medical justification...
... [G]iven what is presently known, continued adherence to a policy of superfluous chemoprophylaxis is disquieting because financial expediency for the veterinarian conflicts with clinical objectvity, and client consent is predicated on unrealistic expectations. Clients mistakenly believe they are purchasing additional protection for their pets, but in reality they are not. If the truth were known to them, few clients would agree to unnecessarily double their expense for heartworm prevention.
But is this the kind of information your vet will tell you?
It is not! And why not? Simple: there's no money in the truth.
And so the vets beat the drum of dependency and over-medication, abetted by the "American Heartworm Society" which is entirely funded by companies that sell heartworm drugs and testing kits. It's a bit like Penzoil writing your car manual and advising you to change your oil every month. Your car mechanic would then point to this manual to justify his services and sales -- and yes he only uses Penzoil in a car like yours! Perfect!