H5N1 Migration Into Southern Vietnam
Recombinomics Commentary
December 20, 2006
Dead poultry were found in water channels early this month but the officials failed to report it to Hanoi.
An H5 subtype avian flu virus resurfaced in Vietnam earlier this year, mainly in ducks and wild storks.
Bird flu first arrived in the delta in late 2003.
The above comments again highlight the relationship of the 2003/2004 explosion of H5N1 in Asia to the current outbreak. H5N1 was initially detected in South Korea and Vietnam in December 2003, which was followed by major outbreaks throughout China as well as Japan, Thailand, Laos, Cambodia, and Indonesia. Human cases were reported in early 2004 in Vietnam and Thailand, followed by human cases in China, Cambodia, and Indonesia in 2005.
The strong linkage to wild birds was provided last year when the Qinghai strain of H5N1 was found in long range migratory birds at Qinghai Lake. This strain was readily disguished from Asia stains, although it shared many polymorphisms with H5N1 isolated in South Korea and Japan in 2003/2004. It also had Asia low path polymorphisms as well as low path and swine polymorphisms found in Europe.
The Qinghai stain was easily identified by its novel cleavage site GERRRKKR as well as PB2 E627K, which was found in H5N1 from a bird for the first time at Qinghai Lake. This strain had the usual property of causing fatal infections in waterfowl, and therefore was easily traced by a path of dead wild and domestic waterfowl. This spread was subsequently detected in Russia, Kazakhstan and Mongolia in the summer of 2005 followed by spread to India, Afghanistan, Europe, the Middle East, and Africa. None of these areas had previously reported Asian H5N1 and all reported the Qinghai strain.
However, sequence analysis indicates avian influenza has been transported and transmitted by wild birds in general, and that distribution includes eastern Asia. In 2002 and 2003 new polymorphisms flew into Hong Kong, which served as a monitor for H5N1 spread in the region. the timing of the outbreaks in late 2003 / early 2004 coincided with wild bird migration coupled with cooler temperatures which stabilized the virus. The current H5N1 in north China trace back to low path avian influenza in Hong Kong in the mid to late 1970's and many of the sequences in northern china are linked to tree sparrow sequences from 2004 as well as Qinghai sequences recombined with Fujian sequences which trace back to ducks smuggled into Taiwan from Fujian province in late 2003 also.
The latest outbreak in Vietnam again points toward migration of H5N1 into the area. Details on the sequence of these new isolates would be useful.
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