February 2, 2006
Protecting People from the Avian Flu
At first glance, Patrick Leahy, PhD, seemed a bit like a duck out of water. Why had the acting director of the U.S. Geological Survey (USGS) been invited to the Johns Hopkins Bloomberg School of Public Health to deliver the keynote address at the January 30 Avian Flu Symposium?
Leahy’s connection with avian flu soon became clear. His agency, USGS—the science arm of the U.S. Department of Interior (DOI)—is charged with overseeing thousands of U.S. wildlife refuges and wetlands, which are home to millions of migratory shorebirds and waterfowl … which in turn are the natural reservoir for the H5N1 avian flu virus.
“All birds are believed susceptible to avian influenza,” said Leahy, “from its mild forms to the highly contagious and fatal form known as highly pathogenic avian influenza—HPAI.” Thus, USGS personnel are now in the thick of pre-pandemic operations, testing live birds, spot-checking hunter-taken birds and studying waterfowl mortality and diebacks. And, of course, trying to protect DOI employees, legitimate bird vendors and the millions of Americans who visit U.S. nature preserves each year.
The brunt of USGS’s work is being performed in Alaska. “We focus on Alaska because that’s where we feel the risk is greatest in terms of migratory birds. Birds from both the East and West intermingle there,” he said. As of January, USGS staff in Alaska had collected and tested tissue samples from over 1,300 birds in their search for the H5N1 virus. They found various Asian flu isolates in 59 samples but no H5N1.
Right now, it takes about a week to turn around a sample, Leahy said, so the search is on for new techniques that will produce quicker results. USGS is also fine-tuning its surveillance methods and boosting its lab capabilities. “We’re trying to get the process streamlined before the migration back to Alaska begins this spring,” he said.
Leahy pointed out that even if no pandemic materializes, the avian flu virus can still have great economic, social and ecological consequences if transmitted to domestic flocks. He pointed to a 1983–1984 eradication campaign in the northeastern United States that resulted in the destruction of more than 17 million domestic birds, cost nearly $65 million and boosted retail egg prices by more than 30 percent. “Early detection and rapid response are crucial,” he said.
Leahy also mentioned in passing that “Maryland’s poultry industry is holding its breath.” Another speaker at the symposium, Ellen Silbergeld, PhD, professor of Environmental Health Sciences, addressed Maryland’s piece of the avian flu puzzle. Silbergeld said the concentration of poultry processing plants on Maryland's Eastern shore—which produce 900 million broiler chickens annually—presents a valuable opportunity for researchers to learn more about the spread of disease from animals to humans.
“We have to understand the animal/human interface to understand the risks,” Silbergeld said, referring to poultry workers’ contacts with tens of thousands of animals during high-volume processing operations. These facilities promote infection and animal-to-animal diseases, and workers typically have no respiratory protection.
Using poultry houses as a research setting, Silbergeld said a question worth asking is, “How can we find out when things are starting to happen in zoonotic systems and moving into human systems?”
Leahy said the task of keeping humans from getting too close to wild birds is made more difficult by the loss of bird habitat to human encroachment and by the growth of the ecotourism industry. Also playing a part nowadays is the lively trade in exotic species. Leahy told of one man who had flown into Brussels, Belgium, with two hawk eagles (an Asian bird of prey) hidden inside his carry-on luggage. Customs agents caught him.
“The two hawks showed no visible symptoms of flu at the time,” said Leahy, “but laboratory tests later revealed that both were infected with H5N1. All the passengers on that flight were contacted and asked to come in for testing—the smuggler was one of the first in line.”
Scientists are now able to implant tiny transmitters inside birds’ bodies and then track the travels of individual birds, moment by moment, in real time. Leahy said the data suggest that if we humans want to catch this virus, we will have to be quick on our feet. “The transmitters show that migratory birds can cover very great distances in very little time.”
Noting that the H5N1 virus had now taken five, maybe six, of the seven classic steps toward a pandemic*, Leahy offered the audience a simple bit of advice: “Don’t touch dead birds.” —Rod Graham
Steps Toward a Pandemic
1. Virus present in host in small region
2. Virus spreads in host across a wide geographic area
3. Virus infects other animal hosts
4. Virus jumps from animals to humans inefficiently
5. Virus jumps from animals to humans more efficiently
6. Virus jumps from human to human inefficiently §
7. Virus jumps from human to human efficiently
§ According to Patrick Leahy, one recent situation in Turkey is particularly troubling because it suggests that H5N1 may be achieving Step 6. In January, a 4-year-old Turkish girl took sick after handling chickens and died. Her mother got sick five days later and died. An aunt, who visited the sick girl and who came from a completely different part of the country, died five days after the mother. “The aunt’s death is not a smoking gun," said Leahy, "but does suggest that H5N1 may be close to accomplishing step six: the virus jumps from human to human inefficiently.”
As of January 30, 2006, 160 human cases of H5N1 had been reported worldwide, with 85 deaths—a 53 percent mortality rate. In the past five years, 180 million birds have been culled in an effort to staunch the flood of disease.