Bird Flu Defies Control Efforts
The spread of avian influenza to at least 29 new countries in the last seven weeks -- one of the biggest outbreaks of the virus since it emerged nine years ago -- is prompting a sobering reassessment of the strategy that has guided efforts to contain the disease.
Since February, the virus has cut a wide swath across the globe, felling tens of thousands of birds in Nigeria, Israel, India, Sweden and elsewhere. Health officials in the United States say bird flu is likely to arrive in North America this year, carried by wild birds migrating thousands of miles to their summer breeding grounds.
The speed of its migration, and the vast area it has infected, has forced scientists to concede there is little that can be done to stop its spread across the globe.
“We expected it to move, but not any of us thought it would move quite like this,” said Dr. David Nabarro, the United Nations’ coordinator on bird flu efforts.
The hope was once that culling millions of chickens and ducks would contain or even eradicate the virus. Now, the strategy has shifted toward managing a disease that will probably be everywhere. Officials are hoping to buy a little more time to produce human vaccines and limit the potential economic damage.
“We cannot contain this thing anymore. Nature is in control,” said Robert G. Webster, a virologist at St. Jude Children’s Research Hospital in Memphis, Tenn., who has been studying the virus since it emerged in 1997.
Formally known as avian influenza A, or H5N1, the virus is rarely transmitted to humans.
There have been 186 human cases and 105 deaths since 2003, according to the World Health Organization. More than a quarter of the deaths -- 29 -- have occurred this year.
Many fear the virus will mutate into a form that is more easily transmitted among people, introducing a deadly flu strain unfamiliar to the human immune system.
Though the virus also could mutate into a harmless strain, scientists have recently found that it has infected domestic cats and a stone marten in Germany, increasing concerns over its ability to cross into mammals.
“Something generally disturbing is going on at the moment,” Nabarro said. “It’s certainly in the bird world, and it’s pushing up against the human world in a serious way.”
For most of its existence, H5N1 stewed in Southeast Asia.
It first appeared in Hong Kong in 1997, infecting 18 people and killing six. The government ordered the culling of all 1.6 million chickens, ducks, quail, partridges and geese in the area to eliminate the virus.
“The slaughter of all poultry in Hong Kong did slow it down,” Webster said. “We thought we had gotten rid of it for quite some time.”
Four years later, the virus resurfaced. Tens of millions of chickens and ducks were killed in Thailand and Vietnam to contain the virus. The sale of chicken plummeted across the region, even though thoroughly cooking the meat destroys the virus.
The outbreak of the virus in Europe and Africa is traced to the discovery last spring of thousands of dead migratory birds at Qinghai Lake in remote western China. The lake is a crucial stopover for many birds that ultimately mix with others that migrate through Europe, Africa and Asia.
Webster suspects that the virus mutated as it circulated among the birds at Qinghai Lake, allowing it to infect wild birds more easily and hitch a ride with them on their long travels.
The genetic fingerprints of the Qinghai strain have shown up in Russia, the Middle East, Europe and Africa.
“Each morning I sit down at the computer ... there’s another country, another outbreak or another human case,” said Nancy J. Cox, chief of the influenza branch at the U.S. Centers for Disease Control and Prevention.
“It keeps us breathless,” she said.
Scientists say the migrating birds could arrive in North America this summer via bird pathways that encompass Alaska and northeastern Canada.
There is no way to stop wild birds, and they can’t all be killed.
“Once it’s in migratory fowl, you really can’t contain the movement of the disease,” Cox said. “In an ideal world, we’d put the spark out, but that’s in an ideal world.”
With the fading hope of containment, governments are considering the controversial option of vaccinating poultry to limit economic damage and reduce human exposure to the virus.
Many countries have hesitated to vaccinate because some vaccinated birds could pick up the virus but not show any symptoms. Those seemingly healthy birds could sicken other birds or poultry workers.
Some experts suspect that the use of substandard poultry vaccines in China in the past helped H5N1 to circulate undetected there.
Japan, Hong Kong and Germany, among other areas, have banned imports from countries that vaccinate poultry, citing the risk of infected meat. The WHO has said there is no danger in eating infected meat if it is properly cooked.
At the end of February, the European Union relaxed its stand against poultry vaccines and allowed France and the Netherlands to inoculate poultry in selected areas.
Russia also approved a mass vaccination program this month, after the government’s efforts to cull more than 800,000 birds did not stop the outbreaks.
“There were reasons in the past not to vaccinate,” said Henry L. Niman, president of Recombinomics Inc., a virus and vaccine research company in Pittsburgh. “Now there has been some rethinking of that because nothing seems to be working very well.”
Most U.S. chicken producers have yet to see the need to vaccinate their flocks, said Richard L. Lobb, a spokesman for the National Chicken Council, whose members produce about 95% of the broiler chickens in the United States.
Lobb said that vaccinating chickens would be a logistical nightmare, and that it would be easier to kill infected birds.
“If you’re vaccinating, you’re basically waiting for something to happen,” he said. “We’d rather go out there and look for something to happen and if we find it, destroy the animals.”
Work on a human vaccine is proceeding, and the CDC has begun stockpiling millions of doses of an H5N1 vaccine undergoing clinical trials.
That vaccine, which was derived from a strain of the virus circulating in Vietnam in 2004, is being produced by Chiron Corp. of Emeryville, Calif., and French drug maker Sanofi Pasteur.
Researchers have begun work on another human vaccine derived from a more recent version of the virus, the U.S. Department of Health and Human Services announced this month. That version is based on a strain harvested from Indonesia in 2005 and is more closely related to strains in Europe, Africa and the Middle East.
The key now, said Cox of the CDC, is buying time to develop vaccines and devise a strategy for using them effectively.
The Los Angeles Emergency Preparedness Department has been brainstorming since April in anticipation of bird flu infections among city employees and their families.
“We’re planning for an absenteeism rate as high as 30%,” said Jim Sims, an emergency planner.