Aug 14, 2006 (CIDRAP News) –The federal government announced today that two swans in Michigan tested positive for both the H5 and N1 avian influenza subtypes, but initial genetic sequencing suggests that it is a low-pathogenic type rather than the highly pathogenic H5N1 strain spreading through birds in Asia, Europe, and Africa and causing deaths in humans.
Ron DeHaven, chief veterinary officer for the US Department of Agriculture (USDA), said at a media briefing today that the birds appeared healthy and normal and were part of a group of 20 nonmigratory, resident mute swans that were sacrificed and tested on Aug 8 as part of a population reduction plan at a game area on Lake Erie in southeast Michigan.
Bill Raub, science advisor to the secretary of the Department of Health and Human Services, said the findings should not cause alarm. "There is no threat to human health, and there is no cause for any special actions," he said. "This is a matter of wildlife biology."
On Aug 9 the samples were tested at Michigan State University's Diagnostic Center for Population and Animal Health, part of the USDA's National Animal Health Laboratory Network, where tests confirmed the presence of an H5 avian influenza virus. The samples were then sent to the USDA's National Veterinary Services Laboratory (NVSL) in Ames, Iowa, which is the only national reference laboratory that can confirm the H5N1 virus.
Confirmatory tests at the NVSL lab showed the presence of an H5 virus along with an N1 subtype; however, experts aren't sure if the birds were infected with two separate avian influenza strains or if the findings represent low-pathogenic H5N1. Testing began at the NVSL on Aug 12 to further characterize the virus, and results are expected in about 2 weeks.
An analysis of genetic sequences at the NVSL has already suggested that the avian influenza virus in the swans is similar to the low-pathogenic avian flu virus identified previously in North America. Routine sampling in wild ducks in the United States showed evidence of low-pathogenic H5N1 in 1975 and 1986. The virus has also been detected in Canada as recently as 2005.
"These results are not unexpected in a given surveillance activity," DeHaven said at the media briefing.
Sue Hazeltine, associate director of biology for the US Geological Survey at the Department of the Interior (DOI), said the agency has taken 8,000 wild bird samples since early June. About 4,000 were from dead birds taken by subsistence hunters in Alaska, and the rest were from live birds. "Less than 2% have shown avian influenza of any type, which is standard and what we would expect to find across the country at any point," she said. None have tested positive for low-pathogenic H5N1.
DeHaven said there is no reason to believe the swans had any connections to any commercial poultry operations, and the findings do not provide a basis for any country to impose any trade restrictions on the United States.
On Aug 9 the USDA and the DOI announced they are expanding wild bird monitoring for H5N1 avian influenza beyond Alaska in partnerships with the lower 48 states, Hawaii, and other Pacific islands. Surveillance in Western states in the Pacific flyway during late summer and fall will coincide with the southward migration of birds that have been exposed to Asian species this summer in the Arctic. Surveillance in Alaska has been under way since summer 2005.
Transcript of Aug 14 USDA/DOI briefing on Michigan swans
Aug 14 USDA fact sheet on low pathogenic vs high pathogenic H5N1 avian influenza
Dec 20, 2005, CIDRAP News article: " H5N1 avian flu viruses: What's in a name?"
Aug 10 CIDRAP News article: "US's wild bird H5N1 monitoring expands beyond Alaska"