First, please double-check to make sure your dog actually has heartworms; different tests mean different things. The most common test evaluates antibodies, which only means the dog has been exposed to heartworms, not that there are still heartworms present.

I am separately emailing you with an article on heartworm management, but if others would like their vets to see it, it was published in the journal “Veterinary Forum” in August 2008. The original is here:
http://www.vetlearn.com/ArticleDetails/tabid/106
/ArticleID/3289/Default.aspx (any vet can sign up for access).

The basic protocol is as follows:
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1. If the dog is symptomatic, attempt to stabilize it with furosemide, angiotensin-converting enzyme inhibitors and, if ascitic, abdominal drainage.

2. Put the dog on a heartworm preventative at standard doses for 2 to 3 months and continue throughout treatment. If using milbemycin, pre-treat with diphenhydramine and dexamethasone for the first dose.

3. Start the dog on doxycycline at 5 to 10 mg/kg q12h for 4 weeks. Studies also have shown that doxycycline-treated heartworms become unthrifty and cease producing microfilariae; the female heatworms become smaller. This reduction in total heartworm mass, along with control of Wolbachia organisms, reduces the morbidity associated with thromboembolisms.

4. Start all dogs on prednisone – if the dog is symptomatic, before giving melarsomine or if the dog is asymptomatic, at the time of melarsomine administration. This is also thought to reduce the lethal complications caused by pulmonary thromboembolisms when you traett with melarsomine. The suggested dose of prednisone is 1 mg/kg/day divided bid and tapered weekly.

5. After giving a heartworm preventative for 3 months, giving doxycycline for 1 month, and starting prednisone if the dog is symptomatic, give one injection of melarsomine. This will kill 30% to 50% of the adult worms. If there are any complications associated with step 5, delay step 6 for another month.

6. One month later, give two injections of melarsomine 24 hours apart. This will kill the remaining worms.

7. Enforce strict exercise restriction during the entire period, not just after giving melarsomine. Any dog with complications should be crated.

– Thomas Nelson, DVM

* Treatment involves off-label use of melarsomine.
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Good luck!
Dr. Jean

In Denver, the prevalence of heartworm is less than 3%. Heartworms have been slowly moving up the Platte and Arkansas River valleys, but the overall prevalence hasn’t changed dramatically. I’ve seen Colorado rated high for heartworm by various organizations, but we have a fairy mobile population; such studies do not take into account where the dog came from or its travel history. The natural transmission rate is very low.

Wow, that’s very informative.

Just so I’m clear:
1-The temp needs to stay above 57 degrees for 8 to 30 days.
2-A mosquito has to bite a dog or cat that already has heartworms and/or microfilaria in it’s bloodstream.
3-That mosquito has to then bite my dog 8-30 days later.
4-I must give my dog heartworm preventative meds within 6 weeks to kill the microfilaria in his bloodstream to prevent my dog from getting heartworms.

Is that correct?
Do you know how prevalent heartworms are in Denver?

You are correct that the treatment for heartworm disease is potentially dangerous, even deadly. You definitely do not want your pet to get heartworms!

However, according to the research I have done, year-round heartworm prevention is clearly unnecessary in most of the country. I am not by any means saying don’t give your pet *any* heartworm preventatives, but simply to give it only when necessary and appropriate. I agree that you can trust most veterinarians to do what’s right for the individual animal, but I also know that most veterinarians are extremely busy and simply take the materials provided by their drug reps and follow those recommendations. My point is that we should not rely solely on the arguments presented by folks who have a financial stake in heartworm medication.

This “debate” just appeared in an April journal article (Ask the Expert: Year-Round Heartworm Prevention: Two Viewpoints, by By Dwight Bowman and James Lok, published in Clinician’s Brief, the official publication of the North American Veterinary Conference, 2009/04/01). Both authors are university professors in parasitology.

The argument presented by Dr. Bowman *for* year-round heartworm medication focused on just two points: (1) the speculation that “scenarios can arise where transmission may occur in cooler climates in the “off season;” and (2) the completely unrelated issue of prevention of internal parasites by additional drugs added to the heartworm preventative.

Arguing on the other side, Dr. Lok lays out the case for appropriate seasonal control, and concludes, “Besides incurring unnecessary costs for the client, indiscriminate application of broad-spectrum medications can engender further confusion about the primary imperative for these medications–heartworm prevention–and when they are most crucial–during the season of heartworm transmission.”

You might find it interesting that in Dr. Lok’s original research (Seasonality of heartworm infection and implications for chemoprophylaxis. Knight DH, Lok JB. Clin Tech Small Anim Pract. 1998 May;13(2):77-82.), the recommendation for Tennessee is to give the monthly preventative from June (to cover infections that may have begun in May) to December (to cover the last possible transmission date in November). I checked with weather.com and these dates seem quite reasonable given the historical temperatures in Memphis. However if–anywhere–the weather is unseasonably warm for long enough, exceptions to those recommendations should be made. I find it even more interesting that this study was funded by a grant from the American Heartworm Society, but its results have never been publicized, least of all to veterinarians.

When looking at a site such as the American Heartworm Society, it’s important to investigate whether that their agenda is truly unbiased. On the Society’s board are representatives from Ft. Dodge and Eli Lilly, and their Vice President works for Merial. These drug companies have a strong financial interest in selling more heartworm products and have been aggressively promoting year-round prevention for all pets, period.

Having looked at both sides of the issue, I have to agree with those who suggest that giving year-round treatment to animals in states where year-round transmission does not occur is doing an injustice to both the animals being given drugs they don’t need, as well as the pocketbooks of their guardians. This argument is rarely presented since the drug companies have the resources to express *their* views in a wider and louder fashion. Since I am neither in practice nor employed by the drug companies, I feel obliged to present that “other side” to our community. Lots of vets and others will disagree with me, but I think there is tremendous value in just having the discussion!