Editor's note: David Quammen is a contributing writer for National Geographic and the author of many books. His most recent, Spillover: Animal Infections and the Next Human Pandemic, appeared last fall.
A deadly new kind of influenza, if it's readily transmissible from person to person, can travel halfway around the planet and blossom on another continent in a day. (See "Tracking the Next Killer Flu.")
Information travels much faster. So does misinformation. Confusion, alarm, misplaced concern, and even panic can move at the speed of electronic gossip, sweeping out ahead of the science, the judicious public health warnings, or any sneezable virus yet discovered.
Those are points to keep in mind as you watch your media sources, over the next few weeks, for updates on H7N9, the newly emerged avian influenza virus that's now killing people in China.
This story broke on March 31, when Chinese authorities announced that a new form of bird flu had been detected in three patients, two men in Shanghai and a woman in Chuzhou City (map), hundreds of miles away.
The two men had died earlier in the month, but laboratory analyses were just now available. The new virus caught the attention of health officials and flu researchers all over the world because this particular subtype, H7N9, has never before been known to infect humans.
Where had it come from? How had it gotten into people? How transmissible among humans, and how lethal, might it prove to be?
Dead Pigs May Be False Lead
Those crucial questions became entangled with a grotesque coinciding phenomenon: thousands of dead pigs floating down the Huangpu River through Shanghai.
Some commentators have speculated that, because swine sometimes serve as intermediate hosts—between birds and people—for influenza viruses, the dead pigs might have been linked to the H7N9 outbreak.
Furthermore, genetic sequencing of H7N9 reveals that while all eight of its gene segments come from viruses unique to birds, some finer mutations suggest an adaptive shift toward infecting mammals.
But there's no evidence that the pigs in the river died of H7N9, and some grounds to doubt it.
According to one flu expert, Malik Peiris of the University of Hong Kong, quoted in ScienceInsider: "It is not expected that any form of influenza would lead to such a huge die-off in pigs."
Meanwhile traces of the virus have been found in pigeons, chickens, and quail, all available at live markets in Shanghai and other Chinese cities, and officials have ordered mass cullings and market closures. If each of the people so far infected caught the virus directly from a bird, as currently supposed, such cullings and market closures might help. (Read Quammen's National Geographic piece "Infectious Animals.")
Then again, this H7N9 bug—unlike the other notorious bird flu, H5N1—doesn't seem to sicken birds, let alone kill them. That makes the problem of determining which stocks of captive birds—or populations of wild ones—might carry the virus very difficult to solve.
And still there's the other mystery: If some mammal is also now carrying the virus, which mammal?
Worldwide concern increased over the past week—emails and online posts and tweets have been flying—as the count of confirmed human cases rose to 24, and the death toll to seven. By the time you read this, those numbers may be higher.
One headline, above a report by a respected journalist, asked: "Is This a Pandemic Being Born?" It may be, or not. But bear in mind that any disease outbreak that spreads globally, whether or not it causes millions of deaths, is by definition a pandemic.
The 2009 swine flu event was a pandemic, worldwide in scope, though it turned out to be far less severe than it might have been. Will H7N9 move beyond China? Will it adapt for transmission from person to person? If so, will it be highly virulent and highly contagious?
Nobody knows, and at this point nobody can know, because influenza viruses are inherently so unpredictable. They mutate continually. Their eight major gene segments snap apart, like Poppit beads, and reconnect with segments from other flu viruses.
(That process, known as reassortment, sometimes happens within pigs.) Because the viruses are so changeable, they're highly adaptive. (Related blog post: "An Infinity of Viruses.")
There's a large element of randomness in their mutation and reassortment, but what emerges and proliferates is whatever proves successful in a given ecosystem. And the human population is an ecosystem offering great opportunity to any highly adaptive virus that can take hold.
It's not a failure of science, nor a sign of cowardice among public health officials, to admit this degree of indeterminacy.
It reflects sober recognition that while vigilance is essential, and quick scientific response is crucial, and every available clue must be factored into planning for what might happen, predicting the course of a new influenza is impossible. You might do as well using guesswork in Las Vegas.
Two dire results could come from the 2013 outbreak of H7N9. One is that it might indeed become pandemic, spreading around the world and causing much illness, disruption, expense, and death.
Another is that after loud warnings have been sounded, if H7N9 proves relatively inoffensive or constrained, almost disappointingly undramatic, the whole experience might contribute to public complacency in the future.
This is the old problem of crying wolf. We know that our flock is vulnerable and faces menace. We see lupine shapes in the dark. We just can't be sure whether the big, bad one will arrive this year or next.