Tests reveal mild avian flu in ducks in 2 states

Oct 18, 2006 (CIDRAP News) – Federal officials announced yesterday that final tests confirmed that a mild strain of H6N2 avian influenza—not the deadly H5N1 type—was found in green-winged teals in Illinois last month. Meanwhile, initial tests on wild ducks in Ohio also suggest a mild strain of avian flu.

In late September, investigators found the virus in Illinois ducks when they collected samples from healthy migratory green-winged teals in Fulton County in west-central Illinois, the US Department of Agriculture (USDA) and the Department of the Interior (DOI) said in a news release. The samples were sent to the USDA National Veterinary Services Laboratory (NSVL) in Ames, Iowa, where 5 of 11 samples tested positive for H6N2.

Initial screening results on Sep 29 indicated that H5 and N1 subtypes might be present, but further testing was needed to confirm the subtypes and assess the pathogenicity. The USDA said it's not unusual for a specific subtype to be identified in initial screening tests but not be isolated in confirmatory testing, because the screening tests are so sensitive.

In this case, rapid screening yielded weak positive results for the H5 and N1 subtypes, but confirmatory testing instead found the H6 and N2 subtypes. Previously announced genetic testing had already ruled out the presence of the highly pathogenic H5N1 strain.

Last week, the USDA and DOI announced that investigators in Ohio had detected H5 and N1 subtypes in samples from apparently healthy wild northern pintail ducks in Ottawa County, in northern Ohio on the shores of Lake Erie. The ducks had been killed by a hunter.

In an Oct 14 news release, the agencies said, "Initial tests confirm that these wild bird samples do not contain the highly pathogenic H5N1 strain that has spread through birds in Asia, Europe, and Africa. Initial test results indicate the presence of low-pathogenic avian influenza virus, which poses no threat to human health."

The birds were collected on Oct 8 as part of an expanded wild bird monitoring program involving the USDA, the DOI, and investigators from the lower 48 states.

Thirty-five samples obtained from the ducks were screened at the Ohio Department of Agriculture Animal Disease Diagnostic Laboratory. Two of the samples were sent to the NVSL for confirmation, and one tested positive for both the H5 and N1 components, which could mean the duck was infected with either one H5N1 strain or two separate avian flu viruses.

Low-pathogenic avian flu viruses often occur naturally in wild birds and cause only minor sickness or no noticeable signs of disease. They pose no risk to human health. However, low-pathogenic strains sometimes mutate into deadly strains.

Recent tests on birds in Michigan, Maryland, and Pennsylvania identified the low-pathogenic "North American" strain of H5N1, and recent tests on wild northern pintail ducks in Montana confirmed the presence of H5N3, another mild strain.

See also:

Oct 17 USDA-DOI news release on avian flu in Illinois ducks

Oct 14 USDA-DOI news release on avian flu in Ohio ducks

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