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H5N1 Bird Flu In Pennsylvania
Recombinomics Commentary

September 2, 2006

The U.S. Departments of Agriculture and Interior today announced that the presence of the H5 and N1 avian influenza subtypes in samples from wild mallard ducks in Pennsylvania.

Testing has ruled out the possibility of this being the highly pathogenic H5N1 strain that has spread through birds in Asia, Europe and Africa. Test results thus far indicate this is low pathogenic avian influenza (LPAI), which poses no threat to human health.

The ducks were sampled August 28, 2006 in Crawford County, Pennsylvania.

The above comments indicate low path H5N1 has also been identified in northwestern Pennsylvania. This detection is not unexpected because H5N1 was found in mute swans adjacent to Lake Erie in southeastern Michigan as well as Queen Anne’s Country in Maryland on the Delmarva peninsula.  It is likely that H5N1 is in wild birds throughout the northeastern United States as well as southern Canada. Thus far all reported isolates are from samples collect in  August.

In August, 2005 Canada reported H5 throughout southern Canada. Although all were low path, H5N1 was only reported for Manitoba.  Other provinces reported H5N2, H5N3, and H5N9.  In the past H5N1 was rarely detected in North America. In the United States, H5N2 was much more common. 

The detection of H5N1 in three distinct locations in the United States suggests that serotype is becoming dominant in the area.  Sequence information may help explain the dominance.  Dual infections in wild birds, including mallard, are common.  Samples collected by Ohio State University are detailed at GenBank and the serotype many of the cloned isolates frequently do not match the initial serotype of the sample, signaling the presence of multiple serotypes in the same wild bird host.

Thus, low path H5N1 could obscure high path H5N1 since they are the same serotype, although the presence of high path should be noted in the biological assay.  Those assays on the Michigan samples indicated the H5N1 was low path.

PCR tests on samples may distinguish samples containing mixtures because the initial tests typically use primers that flank the HA cleavage site and the Qinghai strain of H5N1 would have an additional 12 nucleotides, which would generate a larger insert.

At this time, the factors making H5N1 the dominant H5 serotype are unclear.  Sequence data on the H5N1 in Michigan, Maryland, and Pennsylvania would be useful.

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