the rice paddies. The virus was hard to trace in such circumstances, harder still to eliminate, because infected ducks showed no symptoms. “The duck is the Trojan horse,” Webster told me. That’s where the danger lurked secretly, he meant. Wild ducks might land on your flooded paddy, carrying the virus, fouling the water, and infecting your domestic ducks. Your ducks would appear fine, but when your son brought them home to their coop for the night, they could infect your chickens. Before long your chickens—and your son too—might be dead of bird flu.
“The duck is the Trojan horse,” he repeated. It was a good line, vivid and clear, and I had seen it also in some of his published work. But today he was even more specific: mallards and pintails. The pathogenicity of this virus differs starkly for different kinds of birds. “It depends on the species,” Webster said. “Some duck species die. The bar-headed goose dies. The swans die. But the mallard, and the pintail in particular, carry. And spread.”
Six years after its first outbreak in Hong Kong, H5N1 returned, infecting three members of a family and killing two. As I’ve described earlier, this occurred during the first alarms over what came to be known as SARS, complicating efforts to identify that very different bug. Around the same time, H5N1 started turning up among domestic poultry in South Korea, Vietnam, Japan, Indonesia, and elsewhere throughout the region, killing many chickens and at least a couple more people. It also traveled in wild birds—traveled pretty far. Qinghai Lake, in western China, thirteen hundred miles northwest of Hong Kong, became the site of one ominous event, to which Webster had alluded with his mention of bar-headed geese.
Qinghai Lake is an important breeding site for migratory waterfowl, whose flyways lead variously from there to India, Siberia, and Southeast Asia. In April and May 2005, six thousand birds died at Qinghai of H5N1 influenza. The first animal affected was the bar-headed goose, but the disease also struck ruddy shelducks, great cormorants, and two kinds of gull. Bar-headed geese, with large wing areas relative to their weight, are well adapted to flying high and far. They nest on the Tibetan plateau. They migrate over the Himalayas. They shed H5N1.
“And then presumably,” Webster told me, “the wild birds carried it westward to India, Africa, Europe, and so on.” It got to Egypt in 2006, for instance, and has been especially problematic for that country. “The virus is everywhere in Egypt. Through the commercial poultry, through the duck populations.” Egyptian health authorities tried vaccinating their poultry, with vaccine imported from Asia, but the vaccine efforts didn’t work. “It’s surprising there are not more human cases.” The toll in Egypt is high enough: 151 confirmed as of August 2011, of which 52 were fatal. Those numbers represent more than a quarter of all the world’s known human cases of bird flu, and more than a third of all fatalities, since H5N1 emerged in 1997. But here’s a critical fact: Few if any of the Egyptian cases resulted from human-to-human transmission. Those unfortunate Egyptian patients all seem to have acquired the virus directly from birds. This indicates that the virus hasn’t yet found an efficient way to pass from one person to another.
Two aspects of the situation are dangerous, according to Robert Webster. The first is that Egypt, given its recent political upheavals and the uncertainty about where those will lead, may be unable to stanch an outbreak of transmissible avian flu, if one occurs. His second point of concern is shared by influenza researchers and public health officials around the globe: With all that mutating, with all that contact between people and their infected birds, the virus could hit upon a genetic configuration making it highly transmissible among people.
“As long as H5N1 is out there in the world,” Webster said, “there is the possibility of disaster. That’s really the bottom line with H5N1. So long as it’s out there in the human population, there is the theoretical possibility that it can acquire the ability to transmit human-to-human.” He paused. “And then God help us.”
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This whole subject, like an airborne virus, is at large on the breezes of discourse. Most people aren’t familiar with the word “zoonotic,” but they have heard of SARS, they have heard of West Nile virus, they have heard of bird flu. They know someone who has suffered through Lyme disease and someone else who has died of AIDS. They have heard of Ebola,