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No one knew it at the time, of course, but flu viruses are notoriously unstable-- "genetically labile," as one researcher puts it. Set one flu virus beside another, and the two may trade genes, a process called reassortment. If this reassortment produces a virus that closely resembles one of its parents, it is said to have undergone antigenic drift. On rare occasions, this scrambling can be dramatic. The virus becomes a kind of Frankenstein virus so different from existing strains that the human population has no immunity to it.
In August 1918, the mild virus apparently reassorted into something positively deadly. Outbreaks caused by the new variant exploded almost simultaneously in three far-flung locations: France, Sierra Leone and Boston. The flu struck with a ferocity that shocked doctors, who feared this strange new pathogen might be an airborne version of the Black Death. Patients died awash in blood and gore, literally drowning as fluid filled their lungs.
The virus rocketed to the farthest points of the globe. From September 1918 through March 1919, it killed 33,387 people in New York City, just over 1% of the city's population. In some Alaskan villages, the death toll topped 50%; in one, Teller Mission (now Brevig Mission), 85% were dead within a week.
One of the great mysteries of 1918 centers on who was killed by the virus. Even ordinary flu will cause deaths among the very young, the very old and people with a weakened immune system. The 1918 virus did kill within these groups, but it seemed to have a special passion for the young and hardy, ages 25 to 34, those typically most able to weather the flu.
Rumors flew of strange influenza-like diseases affecting animals, even moose, according to the pandemic's chronicler, Alfred W. Crosby Jr. One rumor turned out to be true--disturbingly so for anyone familiar with the subsequent history of influenza research and the recent Hong Kong outbreak. Farmers in 1918 discovered that something was making their pigs very sick, with high fevers and bad coughs. No such pig flu had ever been noticed before 1918, but every fall thereafter an influenza-like illness attacked the nation's hog population. In 1928 a researcher from the Rockefeller Institute, Richard E. Shope, went to Iowa to investigate the phenomenon, and in 1930 he became the first scientist to isolate an influenza virus. Copies of it are stored today in laboratories around the world.
The 1918 strain of influenza persisted into the '20s, then disappeared, or lost its virulence and faded into the great jigsaw of constantly reassorting viruses. Until lately, the epidemic had almost disappeared from our collective memory as well, prompting Crosby to title his history The Forgotten Epidemic. Among flu experts, however, its mysteries are still current and utterly significant. It has always stood as a vivid warning of what the next pandemic could be like. What made the virus so lethal? Why was it able to kill so quickly? And where in nature did it originate?
Last year flu researchers found themselves asking the same questions once again, but this time because of the strange events in Hong Kong.
THE NEW TERRITORIES