“A disease organism that kills its host quickly creates a crisis for itself,” wrote the historian William H. McNeill, in his landmark 1976 book Plagues and Peoples, “since a new host must somehow be found often enough, and soon enough, to keep its own chain of generations going.” McNeill was right, and the key word in that statement is “quickly.” Timing is all. A disease organism that kills its host slowly but inexorably faces no such crisis.
