People do not realize how often they come into contact with bacteria and viruses. These microscopic And the worst comes in the form of disease. Even though the overwhelming majority of the encounters with microbes go unnoticed, people are quick to respond when a run-in gives them a runny nose, fever, upset stomach, or more severe symptoms. Some bacteria and viruses cause such pain and devastation that they become headline news. Every year novel microbes are discovered and new infectious diseases emerge. It is not big news when a new bacterium is discovered living harmlessly in the soil, but it is broadcast when a virus mysteriously crops up out of nowhere and kills unsuspecting victims.

The first new disease-causing organism to emerge in the twenty-first century was a virus that appeared in a organisms are in...