Commentary
Migration of H5N1 to the European Union
Recombinomics Commentary 18:08
July 1, 2008
Phylogenetic analyses of strains from EU Member States indicated that all H5N1 viruses detected in the EU in poultry and wild birds since 2006 were closely related and belong to clades 2.2 and 2.3. The use of phylogeny can advise on the source of infection, but it is not possible in all circumstances to be definitive about the likely source of an introduction.
All H5N1 viruses detected in the EU in poultry and wild birds since 2006 belong to clade 2.2, the lineage that was first identified during the 2005 Qinghai lake outbreak in China, except for an import case in quarantaine facilities in the UK (clade 2.3). Phylogenetic analyses of strains from EU MSs indicate multiple independent virus introductions, presumably from countries in Eastern Europe or the Middle East, where similar clade 2.2 strains are circulating in poultry and/or wild birds. The use of phylogeny can advise on the source of infection, but it is not possible in all circumstances to be definitive about the likely source of an introduction.
The above comments are from a recent European Food Safety Organization report entitled “Animal health and welfare aspects of avian influenza and the risk of its introduction into the EU poultry holdings”. This first paragraph is from the executive summary, while the second paragraph is the text which was summarized. Although both acknowledge two clades (2.2 and 2.3) in the EU since 2006, the executive summary fails to note that clade 2.3 was in a single import case, which is the exception that proves the rule. Although clade 2.3 (Fujian strain) was detected when quarantined exotic birds died, clade 2.3 has never been reported in EU poultry or wild birds as misrepresented in the executive summary.
Moreover, clade 2.3 has never been reported in poultry, wild birds, or humans outside of eastern Asia. This exception is similar to the H5N1 detected in crested owls being smuggled into Europe from Thailand in 2004. The two birds were detected on a passenger plane and as expected, the H5N1 was clade 1 from Thailand. However, like the clade 2.3 described above, clade 1 has never been detected outside of southeast Asia. Thus, although both clade 1 and clade 2.3 have been detected in birds involved in smuggling or trade, the two exceptions, or undetected related cases, have never produced a reported infection in poultry or wild birds in the EU or any other country not in eastern Asia.
In contrast, all Asian H5N1 in the EU has been clade 2.2, which is transported and transmitted by migratory birds. The role of these birds in the movement of H5N1 over long distances extends to all other countries west of China. None of these countries have reported cases of Asian H5N1 in poultry, wild birds, or people prior to the outbreak at Qinghai Lake in the spring of 2005. This outbreak was followed by the rapid expansion of H5N1 into more than 50 countries west of China, and all infections were clade 2.2.
This type of migration was repeated a year after the Qinghai expansion. In the summer of 2006 a Qinghai subclade (clade 2.2.3) was modified during a massive wild bird outbreak at Uvs Lake in Mongolia. This sub-clade was easily distinguished from other Qinghai sub-clades, including clade 2.2.3 in circulation in early 2006. This Uvs Lake strain migrated to South Korea and Japan in late 2006 / early 2007. It also migrated to the west and was reported in Kuwait in early 2007. Although there were no reported of the Uvs Lake strain in Europe in late 2006 or early 2007, in the summer of 2007 it appeared in wild birds at multiple locations in the Czech Republic, Germany, and France. This was followed by outbreaks throughout Europe in late 2007 / early 2008 and all reported outbreaks in the EU were the Uvs Lake strain.
Similarly, in recent weeks long range migratory birds in northern Japan were linked to clade 2.3 infections and similar sequences were found in chickens in Russia infected with entrails from a wild birds, as well as poultry infected in South Korea. The detection of clade 2.3 in long range migratory birds in northern Japan raises the possibility of expansion of the Fujian strain (clade 2.3) out of eastern Asia.
Thus, the executive summary displayed above is in error, and this type of error continues to confuse a very straightforward geographic expansion of H5N1. The role of trade and smuggling in the long distance spread of H5N1 is minimal. Virtually all of the long range spread of H5N1 in Europe, the Middle East, and Africa is due to migratory birds, which has been confirmed year after year as new waves of H5N1 migrate into the regions.
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