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Friday, May 10, 2013

You Are A Rainforest


Did you know that you are only about 10% human?  Admittedly, the microbe cells are a lot smaller than the human cells so they only add up to 1-3% of our total mass.  But if you're counting cells, microbes that live in and on the body of a healthy adult human being are estimated to outnumber the human cells by about ten to one.  It's an odd thought isn't it?  Makes you feel a bit like a coral reef or a rainforest.  This population of microbes is called the human microbiome.

What are all these microbes?  Well, we actually don't know much about them.  Until recently, the study of our human biome was limited to what would grow in a petri dish....and most microbes just won't grow outside their home habitat.  Due to recent technological advances in genetic sequencing, we are finally beginning to get an accurate look at the billions of diverse ecosystems walking around every morning getting coffee.  If you are interested in the details of this project, do an internet search for the Human Microbiome Project (HMP), funded by the National Institutes of Health (NIH).

What we have already learned is fascinating.  We are born nearly sterile.  During and after birth, we “catch” the mix of microbes that colonize our bodies over our first few months.  The HMP estimates there are approximately 10,000 different species of microbes that commonly inhabit human beings.

Moreover, the microbes that live in my nose are a completely different mix of species from the microbes that live in your nose.  In a way, this is not surprising.  We notice the same thing in rainforests and coral reefs: the exact mix of species can vary dramatically from spot to spot, even when there are no obvious differences in environmental conditions.  But it does raise some interesting questions.  We know that the human microbiome is essential for our health.  But we don't know how to identify a healthy human microbiome!  What does a healthy forest look like?  At what point is intervention required?  At what point does intervention do more harm than good? These same questions must be asked at the microbial level.

All of this new research brings up some serious questions about our “war on germs.”  We used to believe that microbes could be neatly split into categories of beneficial (good) or pathogenic (bad).  But now we're discovering the existence of conditionally pathogenic bacteria.  These bacteria are part of our normal human microbiome.  They are usually harmless or even beneficial.  However, in certain circumstances they can cause disease.

At one time in human history, it was considered desirable to drive a species extinct.  Animals that threatened human beings or their livestock were subject to extermination campaigns around the world.  This made sense at the time.  Who wants to risk the possibility of getting eaten on the way home from work?  Who wants to starve this winter because a predator ran off with most of your livestock?  Trying to exterminate the wolf, the tiger, and other large predators was “common sense” that led to some serious unexpected consequences.  These days, we generally look at that “common sense” as tragic.

Ecosystems are complex things.  Adding or removing a species from an ecosystem can have unforeseen consequences both positive and negative, even if you're looking at a very localized ecosystem.  Does that mean we should never act on an ecosystem?  Well, no.  All living things adjust their local environment, even plants and fungi.  Weeding your garden or setting a mousetrap are attempts to remove certain species from your localized ecosystem.  I certainly have no qualms about keeping mice out of my pantry and morning glory out of my veggie garden!  Nor do I object to planting tomatoes every year, despite the fact that they are not native species.  

But we must also act with caution and intention.  Kudzu was imported to the southeastern area of the US as an attractive, fast-growing plant to control erosion and provide forage for domestic animals.  Now it's called "the vine that ate the south" and is wreaking havoc on the economy, infrastructure, and ecosystem.  During the Great Leap Forward in China, sparrows were nearly exterminated to prevent them from eating grain.  It was subsequently discovered that sparrows prefer to eat locusts and other grain-eating insects.  The net result was a locust swarm that contributed to massive famine.  Approximately 30 million people starved to death.

So it is important to exercise caution when intervening in an ecosystem!  This brings us back to microbes and our current “war on germs.”  Obviously, there are some microbes that are scary, nasty pathogens and which have the potential to make many people very sick.  Living in a world without smallpox is a goal we sought...and achieved.  Similarly, we may be only a few years from eradicating polio!  

But it may be time to question certain aspects of the “war on germs.”  Are antimicrobial washes a good idea?  If so, under what circumstances should they be used?  Antibiotics have saved lives.  However, using an antibiotic is very much like clear-cutting part of our microbiome.  After clear-cutting a forest, what comes back is not what was there originally.  In our part of the world, scotchbroom is quick to colonize newly exposed land...preventing slower growing, native plants from recovering.  How does this look inside of our gut?  Our colon? Our nose?  And, what is the health impact of this change?  Currently, we have very few answers.

And then there are vaccines.  The first vaccine wiped smallpox off the planet, an achievement which we all celebrate.  Polio vaccination - and cleaner water supplies - have nearly eliminated polio, another tremendous achievement.  And now...we have vaccines against 28 different diseases with nearly 300 new vaccines in various stages of development.

What does this all mean for our human microbiome?  Perhaps nothing.  Perhaps everything.  Smallpox and polio vaccines have done wonderful things for humanity.  On the other hand, these successes do not mean that all further vaccines will be such a success.  Decades ago, we had a simple goal: eliminate infectious disease by controlling germs.  That theory is starting to look as woefully simplistic as trying to protect our gardens by killing deer.  Most would agree that building a strong and safe enclosure for a garden works much better...and most health practitioners agree that an ounce of prevention (through a strong and healthy lifestyle) is better than a pound of cure.  

Given that we now recognize the existance of conditionally pathogenic bacteria...what about viruses?  Fungi?  Parasites?  Yup, even parasites might have their benefits.  Active research is currently being done on “helminthic therapy” otherwise known as intentionally giving someone parasitic worms to treat or prevent autoimmune diseases.  It boggles the mind!

You are as delicately balanced as a coral reef or a rainforest.  You are a walking, talking, breathing ecosystem with up to 10,000 different species interacting in a delicate balance.  Amazing, isn't it?

2 comments:

  1. Correction/Clarification:

    I stated above that "we are born nearly sterile". This is not exactly true. Right *before* birth we are nearly sterile. The first colonization with microbes occurs as the baby passes through the vagina during birth. This mechanism obviously does not take place for those born by C-section. Science is still exploring the health implications for newborns who do not get this initial coating of beneficial microbes.

    Karen Crisalli Winter

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  2. Karen Crisalli WinterMay 21, 2013 at 7:58 PM

    Another interesting article on the role of friendly viruses. check it out!

    http://news.sciencemag.org/sciencenow/2013/05/friendly-viruses-protect-us-agai.html?ref=hp

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Welcome to the conversation. Knowledge changes. People respond best when this truism is kept in mind. In community, March & Karen