Triple Threat
The H5N1 avian virus originated in Hong Kong and spread rapidly through much of Asia before continuing to Africa and Europe.
It is fatal to birds and can be transmitted to humans through close contact with birds, for example, on poultry farms.
So far the disease has killed 151 people, but the virus in its current form cannot be transferred from human to human. (Read "Bird Flu: Frequently Asked Questions.")
In his team's current research, Kilpatrick found that the virus spread through Southeast Asia primarily through the poultry trade, but migrating birds were mainly to blame for carrying the disease from Asia to Europe.
"The question now is, How will it get to the U.S.,?" Kilpatrick said.
(See National Geographic magazine's "Tracking the Next Killer Flu.")
Ken Rosenberg of Cornell University's Laboratory of Ornithology was not involved in the study, but he agrees that testing birds in Alaska may not protect the U.S. from the virus.
"To my knowledge, all the testing has been negative. They haven't found it coming in through birds that way,'' Rosenberg said.
Rosenberg thinks it's possible that the virus will come to the U.S. from Latin America, not through migrating birds but through the legal or illegal pet-bird trade.
Mulit-Nation Plan Is Key
Kilpatrick's team found that the virus has spread easily so far due to both the global trade in birds and the migration of wild birds, chiefly geese, swans, and ducks.
The team examined the spread of the virus into 52 countries. In each instance the researchers determined whether transmission occurred through the legal poultry trade, the wild-bird trade, migrating birds, or some combination of these.
The scientists also estimated the number of birds that enter or leave a country, how many of them were likely infected, and how long the birds remained contagious.
The team then ran genetic tests on the viruses found in infected birds, which helped reveal how the virus spread from region to region.
Turkey, for example, has a thriving poultry trade with Thailand as well as a heavy influx of migrating birds from Russia. Scientists weren't sure which pathway brought the virus to the country.
"But then we took a look at the [genetic] isolates, and they were much more related to Russia," Kirkpatrick said.
This led his team to conclude that the likely source of bird flu in Turkey was Russian migrating birds.
The case of Turkey may offer a lesson the U.S., Kilpatrick suggested.
An effective way to keep the U.S. free from bird flu would be to work with Latin American countries on a regional system of testing and quarantining imported poultry, he said.
"If we want to be as safe as possible, we would want all our neighbors to have the same safeguards we do," Kilpatrick said.
His team has not heard from U.S. policymakers about the suggestions put forward in the new study. But Kilpatrick said he hopes decision-makers will refer to the research when considering future bird-flu prevention plans.
"If you're going to make policy decisions, it's best to look at data,'' he said.
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