Unlike bacteria, viruses are not alive.  They are tiny little packages of genetic information that trick normal body cells into doing bad things, like causing disease.  In fact, viruses must invade cells and use the cells machinery in order to replicate.  Viruses come in many shapes but all of them are very small - too small to be seen with ordinary microscopes even.  Viruses are all around us... if someone has a cold or the flu, every time they cough, laugh, or speak they send millions of virus particles floating in the air around us.  If we breath them in, we can become sick too. 

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