I've been thinking alot about parasites lately. It seems to me that "parasite" is like "weed." A weed is simply a plant we don't have any use for, or that is occupying a space or behaving in a way we don't want it to. Same with a parasite: it's something we don't have any use for, or that is present somewhere or doing something we don't approve of.
But I think that's a very humancentric concept, and a very adversarial, "us vs. them" approach, at that. As with everyone and everything else on the planet, the organisms we call parasites have a place and a purpose.
To put this idea to a rigorous, real-world test, I decided to consider one of the nastiest parasites we have in veterinary medicine: heartworm (Dirofilaria immitis). Its place is inside a dog or some other suitable mammalian host. Its purpose presently eludes me, but I believe it does have one. The adversarial view of life would suggest that its "purpose" on the planet, if it has one at all, is to control the population of dogs. While that may well be part of it, I think this view is fundamentally flawed, not to mention incomplete; it just doesn't include all of the facts. I believe that there can - and even should - be a healthy balance between parasite and host, a dynamic that is mutually beneficial.
The benefit to the parasite is obvious: a warm, well-protected place to live, where food is plentiful - that is, as long as the host stays alive. (Note that there is absolutely no benefit to killing, or even harming, the host; because in so doing, the parasite would sign its own death warrant. The idea of parasites as population control just doesn't hold up.)
But what is the benefit to the host? Not to gross you out, but immunologists are now using pig worms to treat allergic conditions in humans. So, one benefit to the parasite-host relationship evidently involves restoring a more healthy immune system response in the host. Whether the host's immune system needs to develop greater vigor or greater tolerance, the presence of a parasite appears able to facilitate it.
Problems arise when there is a lack of balance between parasite and host, or the parasite winds up out of place (e.g. in the wrong host or in the wrong tissue within the right host). Perhaps instead of focusing on killing the worms, we should be emphasizing host health, in the true sense of the word "health" - including physical, psychological, social, and environmental aspects - and restoring a healthy balance between parasite and host, to our mutual benefit. The same is true for the dynamic between host and resident bacteria. That's a fascinating symbiosis... Perhaps I'll write about that next time.
It is possible for a healthy dog to be heartworm positive, and it is just as possible for a heartworm-positive dog to be healthy. It's all about balance. But isn't that true of almost every facet of life?
Stay tuned,
-Dr. Chris King-
Nature's Apprentice
www.animavet.com
