WASHINGTON - Expanded bird flu testing has uncovered H5N1 avian influenza in samples from two resident wild mute swans in Michigan, the U.S. Departments of Agriculture and Interior announced here last week.
To date, the test results indicate low pathogenic avian influenza, which poses no threat to human health and is rarely fatal to birds. Authorities have ruled out the highly pathogenic form of the H5N1 strain that's been responsible for 139 human deaths since 2003.
"It's only the H5 and H7 subtypes, low pathogenic H5 and H7 subtypes, that have ever been known to mutate into a highly pathogenic form," said Ron DeHaven, administrator of USDA's Animal and Plant Health Inspection Service. "So the fact that we are dealing here with what looks like a low pathogenic H5 virus would be reason for concern simply because any H5 or H7 virus has that potential."
HPAI H5N1 has never been found in North America, but LPAI H5N1 has turned up three times: once last year in Manitoba, Canada; and twice in the U.S., most recently in 1986.
"According to the international standards put out by the OIE, or the World Organization for Animal Health, finding of this virus in wild birds should be no basis for any country imposing trade restrictions on the United States and our commercial poultry," DeHaven said.
The news shouldn't affect domestic poultry sales either, said Richard Lobb, spokesman for the National Chicken Council, also here.
"I think it's very clear that this is no big deal and it's nothing to worry about," he said. "Although the H5N1 strain is a little unusual, avian influenza viruses are found in wild birds all the time. I'm not a scientist so I can't say whether a flu strain that is sitting there minding its own business might mutate, but that normally doesn't happen."
Last year, the NCC, in partnership with the National Turkey Federation and the Egg Safety Center, launched the website www.avianinfluenzainfo.com to highlight the fact that HPAI H5N1 doesn't exist in the U.S. and if it did, the disease wouldn't be a food issue. Infected poultry and eggs are safe to eat as long as they are cooked properly. The site provides information for retailers and food-service industry representatives to reassure customers who have concerns, Lobb said.
Earlier this year, NCC established a voluntary bird flu testing program for its members. Since then, more than 10,000 commercial flocks have been tested each month as part of the program.
"We've had no findings of H5 or H7 avian influenza so far and about 96% of [commercial] flocks are covered by the testing," Lobb said.
Although the source of LPAI H5N1 in the resident swans was unclear, DeHaven said there is no reason to believe that the birds have any connection to commercial poultry.
"This finding of an H5N1 strain is not a surprising event to us," said Sue Haseltine, associate director of biology for the U.S. Geological Survey at the DOI. "In fact we have been increasing our surveillance for all avian influenza subtypes throughout wildlife species in this country as sort of an early warning system for this particular strain."
Earlier this year, Gale Norton, the U.S. secretary of the interior, said it's likely that HPAI H5N1 will arrive in North America via migratory bird as early as this year.
In anticipation, the USDA and DOI outlined their plan for expanded bird flu surveillance in March. It includes the investigation of disease-outbreak events in wild birds; expanded monitoring of live wild birds; monitoring of hunter-killed birds; testing of sentinel animals, such as backyard poultry flocks; and environmental sampling of water and bird feces.
Since early June, more than 8,000 migratory birds have been sampled in the U.S. as part of that expanded program, according to Haseltine.
About 4,000 of those sampled were hunted for subsistence purposes in Alaska. These birds are harvested in the spring as they return from their winter breeding ground, many coming from Asia. Four thousand additional samples were taken from live birds that have a history of spending time in Asia during the winter months.
"In that sampling as a whole, we found less than 2% of them to have contained avian influenza viruses of any subtype, and that's about standard for what we would find sampling wildlife species across the country," Haseltine said.
Worldwide there are hundreds of avian influenza viruses, and each can produce varying degrees of illness in poultry. LPAI commonly occurs in wild birds and in most cases it causes minor or no noticeable symptoms.
Earlier this month the USDA and DOI announced plans to increase the expanded surveillance program beyond Alaska to the other 49 states, and to other Pacific Islands as birds from Alaska and Canada begin their southerly migration. Testing in these regions will begin later this month.
"These coordinated federal and state testing programs will be important this fall as birds now nesting in Alaska and Canada begin their migration south through the continental U.S.," said Dirk Kempthorne, secretary of the interior, in a statement.
As part of a strategic plan that outlines an early detection system for uncovering AI in wild migratory birds, the USDA has completed cooperative agreements with 48 states thus far and is finalizing agreements with two states, which covers all 50 states in the four major U.S. migratory flyways. The agreements provide nearly $4 million for state agencies to sample specific species of migratory birds at sites coordinated through the four national flyway councils.
The mute swans tested in Michigan were part of a reduction in population effort unrelated to bird flu testing.
"These birds in fact were sacrificed and then samples were collected from them," DeHaven said. "There is no evidence of any mortality or morbidity, no sickness or dying in that population of birds."
Confirmatory testing is continuing at the USDA's National Veterinary Services Laboratories in Ames, Iowa. The testing will determine the exact subtypes of the virus and confirm its pathogenicity. The results will be completed next week and made public at that time.
"We are providing information about the sampling even though there is little reason for concern because of our commitment to transparency in the testing process," DeHaven said.