News and Highlights: August 2006

WASHINGTON, August, 14, 2006 - The U.S. Departments of Agriculture and Interior today announced that routine surveillance has indicated the presence of H5 and N1 avian influenza subtypes in samples from two wild mute swans in Michigan, but 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 pathogenicity avian influenza, which poses no threat to human health.

Commentary on the strain of H5N1 detected in Michigan swans
Excerpted from: http://www.recombinomics.com/News/08140604/H5N1_Michigan_Sequence.html

H5N1 detected in two of twenty mute swans on Lake Erie in southern Michigan were LPAI (low pathogenic avian influenza). It is likely that the full sequence will be similar top the recently releases HA sequence of H5N1 detected on British Columbia,A/mallard/BC317/2005(H5N2), almost exactly one year ago. However, the exact sequence can provide valuable clues about the presence of the avian HPAI (high pathogenic avian influenza) version of H5N1. In wild birds, that version is most commonly the Qinghai strain.

The Qinghai strain was first identified in May of 2005 at Qinghai Lake. It migrated into southern Siberia for the summer and caused outbreaks in Russia, Kazakhstan, and Siberia. The strain then migrated to Europe, the Middle East, and Africa, as well as China. Sequences of the H5N1 from mute swans in Astrakhan have North American sequences suggesting H5N1 may have already migrated to Canada last year. However, HPAI H5N1 has not yet been reported in Canada.

Do migratory birds spread highly pathogenic avian influenza viruses?
Excerpted from: http://www.who.int/csr/disease/avian_influenza/avian_faqs/en/index.html

The role of migratory birds in the spread of highly pathogenic avian influenza is not fully understood. Wild waterfowl are considered the natural reservoir of all influenza A viruses. They have probably carried influenza viruses, with no apparent harm, for centuries. They are known to carry viruses of the H5 and H7 subtypes, but usually in the low pathogenic form. Considerable circumstantial evidence suggests that migratory birds can introduce low pathogenic H5 and H7 viruses to poultry flocks, which then mutate to the highly pathogenic form.

In the past, highly pathogenic viruses have been isolated from migratory birds on very rare occasions involving a few birds, usually found dead within the flight range of a poultry outbreak. This finding long suggested that wild waterfowl are not agents for the onward transmission of these viruses.

Recent events make it likely that some migratory birds are now directly spreading the H5N1 virus in its highly pathogenic form. Further spread to new areas is expected.

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