The ecosystem of the human body

[haggholm]

These days scientists have a much clearer picture of our inner ecosystem. We know now that there are a hundred trillion microbes in a human body. You carry more microbes in you this moment than all the people who ever lived. Those microbes are growing all the time. So try to imagine for a moment producing an elephant’s worth of microbes. I know it’s difficult, but the fact is that actually in your lifetime you will produce five elephants of microbes. You are basically a microbe factory.

The microbes in your body at this moment outnumber your cells by ten to one. And they come in a huge diversity of species—somewhere in the thousands, although no one has a precise count yet. By some estimates there are twenty million microbial genes in your body: about a thousand times more than the 20,000 protein-coding genes in the human genome. So the Human Genome Project was, at best, a nice start. If we really want to understand all the genes in the human body, we have a long way to go.

[…]

In the September 2010 issue of the journal Microbiology and Molecular Biology Reviews, a team of researchers looked over this sort of research and issued a call to doctors to rethink how they treat their patients. One of the section titles sums up their manifesto: “War No More: Human Medicine in the Age of Ecology.” The authors urge doctors to think like ecologists, and to treat their patients like ecosystems.

[…]

Here’s one crude but effective example of what this kind of ecosystem engineering might look like. A couple years ago, Alexander Khoruts, a gastroenterologist at the University of Minnesota, found himself in a grim dilemma. He was treating a patient who had developed a runaway infection of Clostridium difficile in her gut. She was having diarrhea every 15 minutes and had lost sixty pounds, but Khoruts couldn’t stop the infection with antibiotics. So he performed a stool transplant, using a small sample from the woman’s husband. Just two days after the transplant, the woman had her first solid bowel movement in six months. She has been healthy ever since.

Carl Zimmer, The Human Lake