Monday, March 9, 2009

What Purpose do Parasites Serve?

In the past, I promised not to have too many "end of the world" posts, but this one is just too intriguing.

After dealing with the heckling from some immature friends for having giardia, a parasite that is endemic to the area we live, I got frustrated and began to research why parasites exist. I remember scratching through the itchiest of southern summers wondering how mosquitoes fit into ecosystems. In the end, no matter how grotesque I view mosquitoes to be, they are required to feed birds, frogs, and fish. When I confronted giardia, I had trouble finding the role they and other parasites play in our ecosystems. As it turns out, some scientists devote their lives to the buggers.

From a traditional ecological perspective, parasites act as regulators of species population and as an indicator of ecosystem health. A new study from Ecological Parasitology at the University of California Santa Barbara (UCSB) suggests that parasites also "drive the flow of energy in ecosystems." The findings show that the sheer biomass (weight or volume of organisms in a unit area or habitat) of parasites far outweighs that of free-living organisms. That means little bugs invisible to our eyes encompass more energy in our ecosystem than the things we often enjoy- birds, frogs, and fishes. Even crazier is the power of these microscopic creatures. Add in the energy hosts use to repair the tissue destroyed by parasites to the weight of the parasites and the effect is alarming. To put this into context one scientists explains,
"... in an estuary there are more kilograms of trematode worms - parasites - than kilograms of birds. If you could see the trematodes with binoculars, you might not bother bird watching."[1]
In my case, I can say I spent months of time and energy to get rid of these suckers, but in the greater scheme of an ecosystem, these scientists urge that we cannot ignore the power of parasites. One friend expressed it best, "Eesh, I don't understand if that means parasites are important, but you gotta respect them." The scientists do report that understanding the abundance of parasites will guide future research on how to protect free-living organisms.

Another report from the same research institute touts the importance of parasites in the food web. The article explains that the "pyramid of life" food web that we learned in kindergarten no longer applies. With parasites, there is a second inverted pyramid. Animals at the top have the greatest vulnerability to parasites which pass through prey from the bottom to the top of the pyramid. The study found that on average, food webs contain more links between parasites and their hosts than predators and their prey. The most loving review of parasites comes from study coauthor Andrew Dobson of Princeton University,
"Parasites may well be the thread that holds the structure of ecological communities together."[2]
Let's all jump on the bandwagon and praise the energy suckers! Truthfully, I am slightly in awe of the bugs in my belly, but I still do not understand how I have a condition my body cannot rid of itself. Did native Vermonters deal with this type of indigestion through their lives or did these people have defenses against the endemic parasite? Is pollution making us more susceptible to parasites? I did find one article explaining that nutrient pollution (soil run-off) could be the cause of a surge in parasites that cause deformities in frogs.[3] Perhaps water pollution and an increase and of parasites could explain IBS and humans' digestive issues. No matter what, you have to respect the buggers.

1) University of California - Santa Barbara. "Parasites Vastly Outweigh Predators In Estuaries: Could Have Significant Ecological Implications." ScienceDaily 24 July 2008. 9 March 2009

2) University of California - Santa Barbara. "Study Shows That Parasites Form The Thread Of Food Webs." ScienceDaily 13 July 2006. 9 March 2009

3) Nutrient Pollution Increases Parasite-Drive Frog Deformities


  1. I'm sure I heard something in the news in the last week or two about human parasitic infections appearing to guard against allergy - that we have lived with some of them for so long that our health is impacted now that we can get rid of them. On searching, I didn't find any recent news articles but there was a research paper on the subject from some time ago...

  2. That would make sense. People in third world countries tend to have more defenses against parasites (so when people in the wealthiest countries travel they get sick). This is similar to the idea that antibacterial soaps and cleaners are hurting us. We are in effect setting ourselves up for worse health issues in the future.

    Thanks for the comment.

  3. I do believe that we make ourselves more vulnerable to illnesses, parasites, etc. by our whole stay as clean as possible approach. Nobody used to flinch over a little dirt, we used to rarely take antibiotics, etc. and now super germs and parasites are rampant.

    I also think our eagerness to eat sushi when we have no idea of the quality of the water the originating fish/seafood is extracted from is CRAZY. I only had to read one article about someone getting a parasite from eating sushi to know I am never touching the stuff.

    Dr. Hulda Clark ( advises not to even have any pets because of the potential human issues from their parasites. She's definitely way alternative, but I have done some of her cleanses with great success.

    Last, I am glad we can't see all those parasites when we are enjoying nature!

    FYI--I couldn't get these links to work either. :-(


  4. Shirley,

    My doctor actually advised me to stay away from sushi, which has been slightly difficult for me. It's the destination of choice when I visit my brother or parents. It does bother me to think about the dirty water fish comes from and it is possible I got the parasite form eating sushi.

    It was interesting to read those articles and realize that not everyone views parasites as grotesque things. These scientists seem to have a fascination with them as they indicate health of ecosystems.

    Thanks for the heads up on the links- they are up and running.



  5. Matt--Just think about sushi the way I think about eating gluten ... it would be like willingly eating e coli for me!

    Hope you are starting to feel better! I think all your articles are top notch. I am really enjoying your blog ... even if it about some gross and depressing topics. ;-) Reality, right?


  6. Shirley- I am starting to look at some foods like poison. Which is sad (food should be natural and healthy), but if I focus on what I can eat it's much easier. Plus now I have a dozen instances where I can remember telling myself it was okay to eat a certain food and paying for it later, so by association, those foods are blacklisted.

    I am starting to feel a bit better, but like you said, the healing process may be extensive. I should be up and running (literally) in a month or so. There will be a blog post soon on the updates.

    Thank you for the positive comments!!! It makes all of this screen time worthwhile. I am truly glad that you're enjoying my blog- even the gross and depressing stuff.

  7. Here's a word of thanks from another who reads this blog with rapt attention. Your posts are clear, interesting and informative.

  8. Esmaa,

    Thanks for the glowing comments!

  9. I am starting to look at some foods like poison. Which is sad (food should be natural and healthy), but if I focus on what I can eat it's much easier. Plus now I have a dozen instances where I can remember telling myself it was okay to eat a certain food and paying for it later, so by association, those foods are blacklisted.