Birds from Latin America — not from the north — are most likely to bring deadly bird flu to the main U.S., researchers said Monday, suggesting the government might miss the H5N1 virus because biologists have been looking in the wrong direction.
The United States’ $29 million bird flu surveillance program has focused heavily on migratory birds flying from Asia to Alaska, where researchers this year collected tens of thousands of samples from wild birds nesting on frozen tundra before making their way south.
Those birds present a much lower risk than migratory birds that make their way north from South America through Central America and Mexico, where controls on imported poultry are not as tough as in the U.S. and Canada, according to findings in the latest Proceedings of the National Academy of Sciences.
Nations south of the U.S. import hundreds of thousands of chickens a year from countries where bird flu has turned up in migratory birds or poultry, said A. Marm Kilpatrick, lead author of the study.
Poultry trade riskier than migratory birds
“The risk is actually higher from the poultry trade to the Americas than from migratory birds,” said Kilpatrick, of the Consortium for Conservation Medicine in New York. Other researchers on the study came from the Smithsonian Institution.
If bird flu arrives in Mexico or somewhere farther south, it could be a matter of time before a migratory bird carries the virus to the United States, Kilpatrick said.
“It’s not just a matter of worrying about who you trade with, but it’s a matter of thinking about who do your neighbors trade with, and who do your trading partners trade with,” Kilpatrick said. “We need to be looking both south and north.”
The study concluded that “current American surveillance plans that focus primarily on the Alaskan migratory bird pathway may fail to detect the introduction of H5N1 into the United States in time to prevent its spread into domestic poultry.”
The report is the first to combine the DNA fingerprint of the H5N1 virus in different countries with data on the movement of migratory birds and commercial poultry in those countries.
The analysis helped to determine, for example, that the outbreak of bird flu in Turkey likely didn’t come from poultry imports from Thailand, as previously thought. Instead, the probable source was migratory birds in Russia, where the virus had similar DNA to the virus in Turkey.
The study found that:
- Bird flu was spread through Asia by the poultry trade.
- Most of the spread throughout Europe was from migratory birds.
- Bird flu spread into Africa from migratory birds as well as poultry trade.
U.S. officials cautioned that the study is not the final authority on the spread and prevention of bird flu.
'A big puzzle'
“When you look at scientific literature, it’s a big puzzle. This puts in a few more pieces,” said David Swayne, director of the Agriculture Department’s Southeast Poultry Research Laboratory in Athens, Ga.
Swayne cautioned that researchers looked only at countries’ import restrictions through 2005.
“I’m not saying it’s the fault of the study; the study is designed to look at what happened in the past,” Swayne said. “We have to be very careful not to over-interpret. There is a limit on how recent the data is.”
In addition, Agriculture Department officials said they are not focusing exclusively on Alaska.
More resources have been spent in Alaska than in other states so far, but testing is happening throughout the lower 48, and the U.S. is even helping Mexico do surveillance, said Tom DeLiberto, the department’s National Wildlife Disease Coordinator.
“We have more information now than we did when we designed the surveillance effort last fall,” DeLiberto said.
“We knew that we had limited information and couldn’t design a system that looked at just Alaska,” he said. “You have to build a robust system that could cover a lot of different potential pathways. We know as we get more information, we’ll adapt our system.”
Since the deadly H5N1 virus emerged in Hong Kong in 1996, at least 154 people have died and hundreds of millions of chickens, ducks, geese and turkeys have died or been killed to keep it from spreading.
So far, the virus has killed mostly people who had close contact with sick birds or their droppings, but scientists fear the virus could someday mutate into a form that spreads easily among people.