So here's another set of questions about heartworm treatment where the answer bears repeating. This is a continuation of a dialog that began in a previous post about heartworm treatment. This fellow is out east and has adopted a stray, and unfortunately, the dog has heartworms. At present, he doesn't feel that he can take on the full recommended heartworm treatment with Immiticide to get rid of the adult worms. He has questions about the alternative of just putting the dog on heartworm preventive and trying to "hold the line".
Have you seen young, lightly infected (class 1) dogs overcome a few years of heartworms (maybe
living 2-4 yrs with them and then having no more adult worms due to preventative) and still live decently long lives?
Or is it just ridiculous to think that preventing more adult worms to come and slowly suppressing the ones she has already is okay and not cruel? I worry that just giving her Ivermectin regularly and some doxcycline will be good, but not great, and that years will be taken off her life due to heart damage.
Finally, this is an extremely active dog. She loves to run, jump, and play with our retriever. I
haven't heard her cough or seen her severely out of breath, but it seems this physical activity is not ideal. How much should we cut back? Can she play for a few minutes, or is any exertion just adding more of a chance of heart/artery damage?
The experts say that the severity of disease (actual structural damage resulting in decreased function and shortened life, versus just the presence of worms) is due as much or more to a dog's activity level as to the number of worms present.
Unless there are a huge number of worms (as in a dog that has died from the disease, which would be the picture at the top of the post), they really aren't in the heart, but rather in the pulmonary arteries, those vessels coming from the right side of the heart to the lungs (to get oxygen). If the dog is athletic and active, a more turbulent flow of blood is generated in the arteries by the higher blood pressure and more rapid heart rate. This beats up the inside of the arteries by whipping the worms around.
A relatively small number of worms can thus cause more damage in the athletic dog than would a larger number of worms in the couch-potato dog. The couch-potato dog takes it easy, has a slow heart rate, lower blood pressure, and so the worms are just floating lazily in his blood vessels. They aren't getting whipped around.
When the arteries get beat up, they become inflamed, and they swell. The swelling of the walls causes a narrowing of the open space in middle. This restricts blood flow, causing higher blood pressure in the lungs, and creating increased resistance to the heart's effort to pump blood through the vessels. The heart eventually begins to wear out from constant overwork.
The more often, and more vigorously a dog exercises, the more likelihood that even small numbers of worms will eventually cause significant damage. Unfortunately there is no way to say what magic number of worms will be safe, and even if there were, there's no way to count the worms (at least while the dog is alive).
In our area, you can count on an outside dog having some heartworms by the age of one year if he receives no medication. I have seen many dogs who received no heartworm-preventive whatever lead apparently normal lives until the age of 3 to 5 years, having good exercise tolerance and looking great. Then they begin to show outward signs of decreased exercise tolerance, which progresses eventually to congestive heart failure by less than half of a normal life-span.
SO, if your dog is young, healthy, has very few worms, and you keep giving the ivermectin each month so that he doesn't get any additional worms, then yes, she has good odds for a good quality of life for several years. If she were older, or has more worms, then not such good odds.
It surely would be better to treat the dog for the adult heartworms.