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H5N1 Clade 2.3 in Japan Signals Global and Genetic Expansion

Recombinomics Commentary 05:21
May 15, 2008

it differs from the virus which in the past is verified in the country, presently has become popular in Indonesia and Vietnam

The above comments on the H5N1 in whooper swans in Japan indicate clade 2.1 or clade 2.3 has moved into long range migratory birds.  Comments from South Korea on similarities between the H5N1 there and H5N1 in Vietnam suggest that H5N1 in both countries is clade 2.3 (Fujian strain). Although movement of H5N1 via migratory birds in eastern Asian is not well defined, an elaborate distribution route in areas west of China has been defined by surveillance and analysis of clade 2.2.

Clade 2.2 was initially reported at Qinghai Lake in central China in May, 2005.  The spread outside of China was first reported in outbreaks in Siberia and Mongolia in the summer of 2005.  The high concentration of H5N1 in long range migratory birds suggested H5N1 would migrate into Europe, the Middle East, and Africa, where it had never been reported previous.  These predictions were confirmed by reports of H5N1 in these regions in late 2005 and early 2006.  All isolates were clade 2.2, which was also found in south Asia in India, Afghanistan, and Pakistan.

In the summer of 2006 a new wild bird outbreak was reported at Uvs Lake in Mongolia.  This clade 2.2.3 strain subsequently migrated to the east in South Korea and Japan in late 2006 and early 2007.  The Uvs Lake strain also migrated to the west, and was reported in Kuwait in early 2007.  Although there were few reports of H5N1 in Europe in late 2006 and early 2007, outbreaks were reported in the Czech Republic, Germany, and France in the summer of 2007.  All outbreaks were the Uvs Lake strain, which was subsequently widely reported in Europe and Saudi Arabia at then end of 2007.

Although there was considerable heterogeneity in the H5N1 in circulation, all isolates were clade 2.2.  The reports of clade 2.3 in whooper swans in Japan and poultry in South Korea raises concerns that the clade 2.3 will follow the paths of clade 2.2 and increase the geographical reach and genetic complexity of H5N1.

The outbreaks in South Korea are at record levels and the locations in Japan are further north than prior outbreaks.  The detection of these outbreaks in late spring raises concerns that the H5N1 was brought into the area recently by birds migrating north in the East Asian flyway.  Japan and Korea are within intersecting flyways that can move the clade 2.3 into Siberia and Mongolia, while northern movement along the east Asian flyway would move clade 2.3 into North America.

The mixing of clade 2.2 and clade 2.3 in migratory birds could lead to significant recombination and genetic drift, which may then move into new regions as evidenced by the new locations in Japan and the high concentration of H5N1 in South Korea.

Primorie has already reported H5N1 for the first time and its proximity to South Korea and Japan raise concerns that clade 2.3 has already moved into Russia.  Details on the sequence of the H5N1 in Russia would be useful.

Enhanced surveillance in Russia and Mongolia, as well as Alaska is warranted by these new movements of H5N1 and the first reports of clade 2.3 in Japan and South Korea.

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