Dictionaries define that for something to “emerge” it has to rise from an obscure or inferior position. One could say that humans, by vanquishing the threats of infectious diseases, have emerged as one of the dominant species on the planet. But an ominous foreshadowing of the history of infectious diseases is contained in another dictionary definition of “emerge,” in which emergence refers to coming into being through evolution.
While the human species has developed an armamentarium to ward off the known infectious threats to health, the microbial world has not been idle. One only has to peruse newspaper headlines to realize that reports of emerging infections are increasing at an alarming rate. Humans around the world are continually battling viruses, bacteria, prions, and parasites. Sorting through the plethora of new infectious threats to human health and biosecurity can be daunting, even for infectious disease specialists. The rapid-fire pace with which new discoveries of unknown pathogens are announced makes most textbooks irrelevant when it comes to this topic, and one is left to use Internet search engines when colleagues or patients inquire about some exotic new infection creating havoc on the other side of the globe. A recent review on this topic begins with a fitting 19th-century quote from Rudolf Virchow: “Not a single year passes without [which] . . . we can tell the world: here is a new disease!”1