And, indeed, as he listened to the cries of joy rising from the town, Rieux remembered that such joy is always imperiled. He knew what those jubilant crowds did not know but could have learned from books: that the plague bacillus never dies or disappears for good.
-- Albert Camus, The Plague
Over the last decades we have become more aware of the importance and dangers of emergent diseases. New and old viruses and bacteria come and go, sometimes as phantoms (Figure 8. 1). Oliver Sacks, in Awakenings, 1 tells the story of one of the most recent but forgotten pandemics: the sleeping-sickness disease. It was apparently first noticed in the winter of 1916-1917 in Vienna and other European cities, and it spread rapidly over the next three years until its distribution was worldwide. The illness itself was rather puzzling: "manifestations of the sleeping-sickness were so varied that no two patients ever presented exactly the same picture." It was as if "a thousand new diseases had suddenly broken loose." Later, systematic work identified the cause of this outbreak as a virus. The pandemic finally retreated, like the plague in Albert Camus's novel. "It took or ravaged the lives of nearly five million people before it disappeared, as mysteriously and suddenly as it arrived, in 1927."