Surviving Within the Host and Exiting the Host

A pathogen or infectious agent is a microorganism such as a virus, bacterium, prion, or fungus that causes disease in its host.

A pathogen's success depends on its ability to evade the host's immune responses.

Virulence regulation is a combination of the specific traits of the pathogen and the evolutionary pressures that lead to virulent traits.

Pathogens must have a way to be transmitted from one host to another to ensure their species' survival.