By DONALD G. McNEIL Jr.MAY 4, 2015
Although much of the country has barely noticed, avian influenza — a version of the virus that generated “Killer Bird Flu!” headlines a decade ago — is now sweeping the Midwest.
More than 20 million turkeys and chickens have died or been culled; Iowa, Minnesota and Wisconsin have declared states of emergency; and teams of experts are trying to figure out how the new virus is spreading.
No humans have caught this flu, but health officials fear they might. They are requiring that cullers and barn-cleaners wear the kind of protective gear that Ebola workers do. Officials have also advised that everyone who was recently in contact with affected poultry operations — workers, truckers, veterinarians and so on — take Tamiflu, a flu preventive.
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The H5N2 and the new H5N1 have some North American genes and so clearly emerged on this continent more recently — presumably when the H5N8 virus finally arrived and crossed with North American strains.
That may have happened last summer. Migratory ducks, geese and swans from around the world share ponds in the Arctic in summer. New flu gene mixes emerge and move south along the various migratory paths taken by the birds.
Whatever the mix of genes, dose size is also important in determining spread of the virus, said Dr. Peter Palese, a flu expert at the Mount Sinai School of Medicine.
Human flus can infect people who inhale only one to 10 virus particles, he said, but it takes 100,000 to 1 million particles of an H5 bird flu to infect a human.
“That’s why people who sleep under their chickens in markets in Asia get it, and we don’t get it on Fifth Avenue,” Dr. Palese said.
In birds, flu is primarily an intestinal disease rather than a respiratory one, so cullers and cleaners are told to wear coveralls, face masks and goggles to prevent any barn dust — much of which is powdered feces — from entering their noses, mouths or eyes.
Dr. Palese says he believes they should wear the full hoods with battery-powered air filters used in biosafety Level 3 laboratories.
Officials, he said, should also consider giving them the vaccines developed years ago against H5N1. Although it would not be a perfect match, it might provide some protection.
Several million doses of an experimental vaccine are in the National Strategic Stockpile, said Dr. Anthony S. Fauci, the director of the National Institute for Allergy and Infectious Diseases.
It was created in the early days of panic over the Asian H5N1.
Blood samples from people who received the experimental vaccine years ago are now being tested to see if they contain antibodies that help protect against the new flus, a C.D.C. official said.
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