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Fujian H5N1 Evolution and Global Expansion
Recombinomics Commentary 21:22
May 24, 2008

The recent sequence data from Japan and Russia and the reported identities of 99.7% or greater with the isolates from South Korea clearly demonstrate a global expansion of the Fujian (clade 2.3) strain of H5N1.  None of these countries has previously reported the Fujian strain, raising concerns that the strain is poised for a dramatic global expansion similar to the expansion of clade 2.2 which began in the spring of 2005 at Qinghai Lake.  Clade 2.2 migrated to Chany Lake  in Novosibirsk in Siberia and the Erhel Lake in ongolia in the summer of 2005, and then spread to Europe, the Middle East, and Africa in late 2005 / early 2006 as well as south Asia in the same time frame.

Clade 2.3 traces back to an isolate from ducks being smuggled from Fujian province to Formosa in late 2003, A/duck/China/E319-2/03.  In contrast to the consensus HA cleavage site of RERRRKKR, the Fujian strain was missing a K, producing the cleavage site of RERRRK_R.  The strain expanded in China and a more evolved version, A/duck/Fujian/1734/2005 was isolated in the spring of 2005 and it spread throughout southern China in the 2005/2006 season.  This Fujian strain was also found in wild birds in Hong Kong in early 2006 as well as isolates from Laos and Malaysia, signaling movement into southeast Asia.  In 2005 China reported its first human case and it, like virtually all human cases in China was clade 2.3,

As more sequences were developed, clade 2.3 was divided into multiple sub-clades.  The 2003 duck isolate was clade 2.3.2, as were poultry isolates in Vietnam in 2005.  The vaccine target for clade 2.3.2 is A/common magpie/ Hong Kong/5052/2007, although the sequences fro this isolate have not been made public.  However, it is in the WHO phylogenetic tree of vaccine targets, and maps to the same location as the HA sequences from Japan, and presumably Russia and South Korea.

The largest Fujian sub-clade is 2.3.4, which includes the 2005 isolate from Fujian province as well as all clade 2.3 human cases in China.  Human cases from Laos and Vietnam are also clade 2.3.4.  The sequences from Japan and Russia (and presumably South Korea), other than HA are clade 2.3.4 and are most closely related to a human isolate from Guangdong Province, A/China/GD02/2006, which is closely related to the wild bird sequences from Hong Kong in 2006.

Thus, the sequences in Japan (and presumably Russia and South Korea) are reassortants, with an HA from clade 2.3.2 and the other seven gene segments from clade 2.3.4.  The H5 infection of the soldier in South Korea represents the first reported human infection involving HA from clade 2.3.2.

Thus, it is the Fujian reassortant of clade 2.3.2 / clade 2.3.4 that is poised to spread into North America via the East Asia flyway and poised to mix with clade 2.2 in Mongolia via clade 2.3 infected wild birds in South Korea which migrate to Mongolia during the summer.

This global expansion of Fujian clade 2.3 is an increasing cause for concern.

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