A pathogen (from Greek πάθος pathos "suffering, passion", and γἰγνομαι (γεν-) gignomai (gen-) "I give birth to"), infectious agent, or (more commonly) germ, is a biological agent that causes disease or illness to its host.[1][2] The term pathogen is derived from the Greek "that which produces suffering." There are several substrates and pathways whereby pathogens can invade a host; the principal pathways have different episodic time frames, but soil contamination has the longest or most persistent potential for harboring a pathogen. Pathogen is known to cause diseases which attack the nerves.

http://en.wikipedia.org/wiki/Pathogen