What is a pathogen?

A pathogen or infectious agent is a biological agent that causes disease or illness to its host. The term is most often used for agents that disrupt the normal physiology of a multicellular animal or plant. However, pathogens can infect unicellular organisms from all of the biological kingdoms. Today, while many medical advances have been made to safeguard against infection by pathogens, through the use of vaccination, antibiotics and fungicide, pathogens continue to threaten human life.