Between fevers, congestion and diarrhea, there are numerous ways that microbes can make us feel sick. But just how do microorganisms cause these symptoms?
At any given time, the microbes inside of our bodies outnumber our own cells by at least 10 to 1. In general, these tiny organisms are harmless — and often beneficial — to us, but some bacteria, viruses, fungi and protozoan parasites cause nasty diseases. For example, Escherichia coli can cause diarrhea, rhinovirus is behind the common cold and the fungus Cryptococcus neoformans can bring about a severe form of meningitis.
As you've probably guessed, there is no singular way that microbes make us sick — different biological mechanisms underlie different disease symptoms. So let's go over some of the ways that microbes cause different symptoms. (Note: This is a general guide and is in no way meant to be a comprehensive description of every symptom you could possibly get.)
For the rest of the story: http://io9.com/the-truth-about-why-microbes-make-you-sick-471481771