Spreading Its Wings
It's only a matter of time before Bird flu reaches the United States. Can we stop the killer virus?
Steven Hinrichs delights in watching the sandhill cranes that soar along Nebraska's Platte River each March on their spring migration north. This year, that delight has turned to dread. Hinrichs directs the University of Nebraska's Center for Biosecurity, and he knows that birds can bring not only beauty but also death. "I don't think it's a coincidence," he says, that the 1918 flu pandemic, which killed perhaps 50 million people worldwide, originated nearby.
Nebraska is on the famed Central Flyway, a route that millions of birds follow each year as they migrate from southern wintering grounds north to Alaska and the Arctic to breed. While there, the birds often mingle with birds from Asia, where H5N1 avian flu, widely regarded as the bug most likely to mutate and spark a human pandemic, is rampant. When the sandhills return in the fall, Hinrichs wonders, "what will they bring back?"
He's not the only one asking that question. David Nabarro, the United Nations' bird flu czar, said last week that he expects bird flu to reach the Americas in a migratory bird in the next six to 12 months. Federal agencies announced ramped-up efforts to detect H5N1 in wild birds. "We expect H5N1 to arrive in the United States," Agriculture Secretary Michael Johanns told U.S. News last week. "If migratory birds can spread it, and we're heading into spring, we need to be prepared." The goal is to create a system to detect the virus's entry into North America early on. With more notice, infectious disease specialists hope they can slow the contagion among wild birds and poultry, thus reducing odds that it will jump to humans or, in the worst case, mutate and gain the ability to spread from human to human, setting off a deadly pandemic. Even without a pandemic, the advent of H5N1 could have enormous economic impact. Although only one commercial poultry farm in Europe has been infected, poultry sales there have plummeted as much as 70 percent in the past month--even though eating cooked chicken doesn't pose any risk.
Starting in April, researchers from several federal agencies will test roughly 100,000 birds, dead and alive, as well as bird feces, in Alaska, Hawaii, and the lower 48. The survey was launched in 1996; this year's endeavor will test eight times as many birds as in the previous years combined. The samples will be run through a network of 39 federal, state, and university laboratories equipped to do rapid polymerase-chain-reaction testing, which copies bits of DNA, and can handle 18,000 samples a day, part of a national laboratory upgrade funded by post-9/11 federal bioterrorism programs.
Natural step. "There's little question in my mind that we will at some point see a wild bird [with H5N1] enter our domain," says Michael Leavitt, secretary of health and human services, who convened summits last week with officials in North Dakota and South Dakota to discuss pandemic flu preparations. "We don't view that as a crisis; we see that as a natural step along the path. It would not be unusual, seeing what's happening in the rest of the world. "As part of its pandemic flu precautions, the United States is buying 19.5 million courses of antiviral drugs, but no one knows if they will work against H5N1. The feds are also testing experimental vaccines, but because domestic vaccine production facilities are lacking, it will take at least six months from the start of a pandemic to make significant amounts. Thus, the hope that surveillance will bring early warning and more time to mount a response.
The need for surveillance, a time-honored technique in infectious disease control, is particularly acute because no one knows exactly how the H5N1 virus has spread so far, so fast. Avian influenza has been around for at least a century in both wild and domesticated birds. But until recently, outbreaks of virulent strains in poultry were exceedingly rare. The H5N1 virus first appeared in 1997, when thousands of chickens in Hong Kong suddenly sickened and died. That outbreak was halted when public-health officials ordered the slaughter of all the poultry in Hong Kong. The virus re-emerged in Southeast Asia in 2003 and proliferated rapidly. That outbreak continues, and efforts to contain it by culling flocks or vaccinating birds, measures that had worked in the past, have failed. At least 97 people are known to have died from bird flu since 2003. Almost all of them lived in households with backyard poultry flocks.
But in the past year, avian influenza has started to kill wild birds, which had long been able to harbor the disease without getting sick. In April 2005, more than 6,000 bar-headed geese died at Qinghai Lake in central China, a congregating point for migratory fowl. That was a wake-up call to wildlife biologists; the last time avian influenza afflicted large numbers of wildfowl was in 1961. "That's the really surprising part of it, that wild birds are now being killed by this virus as well," says Leslie Dierauf, director of the USGS National Wildlife Health Center in Madison, Wis. "It's changed somehow, and we're not sure how."
Indeed, three months after the Qinghai Lake die-off, poultry in Western Siberia started dying of H5N1. The virus has spread like wildfire since then, first moving through Central Asia into Turkey and eastern Europe. Those viruses, when tested, proved almost identical to those recovered from the birds at Qinghai Lake.
In the past three months, the H5N1 virus has gone ballistic, infecting birds in 21 countries in Africa, Europe, and the Middle East. It's unclear if the outbreaks are the result of bird migrations, poultry shipments, or other human activities. In some countries, like Nigeria, only poultry has been infected. In others, like Germany, only wild birds are dying. The uncertainty has set off a fierce battle between some wildlife conservationists, who feel that wild birds are being unfairly maligned, and agricultural interests.
"Who is the spreader?" asks Robert Webster, a bird flu authority at St. Jude's Children's Research Hospital in Memphis. Webster, working with colleagues in Asia, reported last month that H5N1 is widespread in migratory birds in southern China, suggesting that they could carry the virus long distances. Webster says he's less concerned about the dead birds found in recent weeks in Europe than he is about those still aloft. "Dead birds don't migrate."
Testing flocks. Commercial poultry growers in the United States are acutely aware of the risk posed by H5N1, not the least because they've been dealing with less lethal and more common forms of bird flu for decades. The highly pathogenic H5 and H7 strains are both rare and more lethal, killing 80 to 100 percent of the birds infected. The United States has had three outbreaks of these strains, in 1924, 1983, and 2004; slaughtering the birds and disinfecting the farms contained them. In 2003, the Netherlands killed more than 30 million birds to arrest an outbreak of H7N7 bird flu. Other countries, notably China, have used vaccines, but the United States and most European nations eschew that method, arguing that vaccinated birds can act as carriers and infect others. If H5N1 attacked U.S. poultry flocks, producers would use the slaughter, quarantine, and sanitation techniques that have worked in the past, says Richard Lobb, a spokesman for the National Chicken Council. Almost all commercial poultry is raised indoors, and in January the large producers, which account for 95 percent of the chicken sold in the United States, started testing all flocks for H5N1.
"The poultry industry in the United States is well prepared to detect and manage an outbreak," says Nina Marano, associate director for veterinary public health for the Centers for Disease Control and Prevention, who specializes in zoonoses, or diseases like H5N1 and West Nile virus that pass from animals to humans. She frets more about protecting the country's approximately 50,000 hobby flocks, as well as exhibition birds and live poultry markets.
The country's major zoos, which are shelters of last resort for endangered species, and also commonly host chickens, wild ducks, and geese, are buttoning up plans to deal with H5N1. Those range from shutting down walk-through aviaries to quizzing visitors on their recent travels. "You can't eliminate wild birds," says Robyn Barbiers, a veterinarian at Chicago's Lincoln Park Zoo who chairs the American Zoo and Aquarium Association's animal health committee. When West Nile virus arrived in the United States in 1999 and started killing wild birds, everyone was nervous, she says. "We dealt with it," says Barbiers. "I don't think avian influenza is going to be as disastrous as people envision."
But H5N1 could prove disastrous in countries like Nigeria, where the virus has been detected on more than 130 poultry farms in the past month. Webster says when he lies awake worrying, it's about places like Africa where lab capacity, cash, and expertise are all scarce. "I worry that the virus will end up in humans and not necessarily be detected," he says. It would take just one sick person on an overseas flight to ignite a pandemic.
Last week, health officials from around the world met in Geneva to talk about how to stop a pandemic--something that has never been attempted, let alone realized. Intensive surveillance of animal and human flu cases would be essential to containment, providing enough time to vaccinate people and treat them with antivirals before the disease could spread.
Until H5N1, notes Webster, the world wasn't interested in bird flu. "Who gives a damn about a virus that's out there in wild birds and doesn't do anything? Now we know," he says, "that we do have to understand the natural history of these things, because they do have consequences."
Since 2003, the deadly H5N1 strain of avian influenza has spread from its origins in Asia into Europe and Africa, infecting millions of birds. At least 96 people have died.
First confirmed cases of H5N1 flu in birds
Sources: World Organization for Animal Health; World Health Organization
This story appears in the March 20, 2006 print edition of U.S. News & World Report.