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HIPPOCRATES DESCRIBED THE SYMPTOMS of the flu some 2,400 years ago. But the influenza virus didn't become a true menace until the rise of stable, densely populated settlements and the growth of animal husbandry. This crowding of people and their animals furnished the virus with ample opportunities to jump from one species to another, acquiring deadly attributes along the way.
The first influenza pandemics were recorded during the 1500s. The one that occurred in 1580 traced a path that epidemiologists today would recognize: it began in Asia during the summer and then spread to Africa, Europe and America over the next six months. Another big epidemic hit in 1789, the year that George Washington took office, “before modern means of rapid travel were available and when a man could go no faster than his horse could gallop,” wrote virologist and epidemiologist Richard E. Shope in 1958. Even so, he said, it “spread like wildfire.”
Shope knew influenza well: in 1931 he became the first scientist to transmit the virus between two animals, by transferring mucus from one pig's nose to another's. Because Shope had filtered bacteria from the mucus beforehand, his experiment suggested, for the first time, that the flu was caused by a virus. Two years later a group of U.K. scientists became the first to isolate a human form of the virus, from a sick ferret.