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Evidence for H5N1 Wild Bird Flu Migration
August 29, 2005
"There is a constant, low-level risk of a low-pathogenic strain being introduced, but there is no evidence that the highly pathogenic virus is spread by migrating birds," Dr Reynolds said.
Since policy makers are still claiming a lack of evidence of HPAI H5N1 being spread by migratory birds, it is worthwhile to review the evidence.
The H5N1 from Asia is HPAI based on a number of criteria. In May of this year, bar headed geese were dying at Qinghai Lake. Sixteen isolates were sequenced and the virus was highly pathogenic by a number of criteria, including death of experimental chickens within 20 hours of infection.
Although the H5N1 had the diagnostic multi-basic cleavage site found in HPAI in Asia and was closely related to H5N1 isolates from Guangdong Province in China as well as Japan and South Korea, the Qinghai sequences were unique. In addition, these isolates had the unusual property of causing death in migratory waterfowl.
Deaths of waterfowl in adjacent Xinjiang province were reported a few weeks later, and the OIE reports by China indicated migratory birds were responsible for the infection of the domestic ducks and geese.
However, the outbreaks at the nature reserve in Novosibirsk provide the strongest evidence for migration of H5N1. Although there was a surveillance lab operating at Chany Lake, H5N1 related to the Asia version had never been reported at Chany Lake. LPAI versions had been reported and a sequence for H5N3 had been deposited. However, this sequence was similar to H5N2 and H5N3 from Primore as well as locations in Europe.
The H5N1 at Chany lake this year was closely related to the H5N1 at Qinghai Lake. Thus, HPAI was reported to OIE from Russia for the first time this month.
These repots from Russia were followed by similar reports from Kazakhstan and Mongolia, two other countries that had never reported H5N1. In Mongolia, the outbreaks were at remote nature reserves and also involved migratory waterfowl. These outbreaks subsequently migrated east. In contrast the parallel outbreaks in southern Russia and northern Kazakhstan migrated west (see dynamic map).
All of these data strongly support transmission and transportation of HPAI by migratory birds. H5N1 was also detected in a wild duck shot down in the Republic of Altai, providing additional evidence for the transport of H5N1 by migratory birds.
Thus, the continuing migration of H5N1 and infections of wild migratory waterfowl at remote nature reserves provides ample evidence for transmission of HPAI H5N1 by migratory birds.