There was an interesting article in this last weeks New Scientist magazine entitled "Befriending the Body Snatchers" which talks about parasitic organisms that take over their host's brains. I can't find an online posting of it, but it talks about things like ophiocordyceps camponoti-balzani (http://www.impactlab.net/2011/03/06/zombie-ants-controlled-b...), Gordian worms (http://en.wikipedia.org/wiki/Nematomorpha), Entomophthora (http://en.wikipedia.org/wiki/Entomophthora_muscae), sacculina (http://en.wikipedia.org/wiki/Sacculina), and also the use of things like Beauveria Bassiana(http://en.wikipedia.org/wiki/Beauveria_bassiana) as a way to fight malarial mosquitoes. Interesting stuff, now if only it was posted online... :(

This reminded me of an excellent read: http://www.damninteresting.com/a-fluke-of-nature/

I read this and immediately thought of a recent freakonomics podcast: http://freakonomicsradio.com/the-power-of-poop.html

As someone who suffers from IBS and lactose intolerance, I am excited about the possibility of this field of research.

on a related note: http://en.wikipedia.org/wiki/Toxoplasma_gondii