H5N1 Migration in South Korea
Recombinomics Commentary 07:95
April 13, 2008
There were two prior HPAI outbreaks in the ROK as a result of infected migratory birds. These outbreaks occurred in poultry farms 15 Dec 03 to 5 Feb 04, and then again 22 Nov 06 to 8 Mar 07.
The above comments from the US Forces in Korea are a refreshing change in the description of the H5N1 outbreaks in South Korea (and elsewhere). The report includes maps of the above outbreaks and the above description leaves little doubt that the poultry outbreaks are due to migratory birds.
The role of migratory birds in the transport and transmission of high pathogenic H5N1 was settled in the summer of 2005, but media reports, as well as reports from Promed and some blogs continue to misinform the general public on this issue by suggesting that there is a scientific debate on this issue. These news outlets are supported by similar misinformation from conservation and bird watching groups, which continue to create confusion on this very straightforward and obvious method of H5N1 distribution.
In South Korea the two earlier outbreaks corresponded to wild bird migration. The 2003/2004 outbreak signaled the start of a major geographic expansion of H5N1 out of China. Japan also reported H5N1 outbreaks and subsequently published sequences from wild resident birds, which were closely related to the sequences in South Korea.
However, the major signal for long range migratory bird transport and transmission of H5N1 happened in the spring of 2005 when a massive outbreak was reported at Qinghai Lake in central China. Initially all dead birds were bar-headed geese, which can fly 1000 miles in 24 hours. The OIE report listed 5 long range migratory bird species, but the large number of species that visit the nature reserve in the spring suggested that the number of infected species was much greater.
Sequences published in Nature and Science in July, 2005 showed that the species was novel, but related to the H5N1 from South Korea and Japan in 2003/2004. This sequence data alone suggested that distribution by long range migratory birds had been ongoing, but at a level that was not detectable or reportable, because no country west of China had reported H5N1.
In mid-July however, H5N1 was reported at Chany Lake in southern Siberia. The OIE report attributed the outbreak to wild birds and noted that the first farms to be affected were those that shared small lakes with wild birds. The reports also included sequence data showing that the H5N1 in Russia was also the Qinghai strain. Thus, by the summer of 2005 there was little doubt that migratory birds could transport and transmit H5N1 over long distances, since the location in Siberia was thousands of miles from Qinghai Lake. Moreover, H5N1 was isolated from a healthy crested grebe, and that H5N1 was also the Qinghai strain.
The final blow came in August of 2005, when wild birds began dying at Erhel Lake in Mongolia. The location of the remote lake relative to outbreaks in China and Russia, as well as the lack of poultry farms in the area once again provided compelling evidence that H5N1 was transported thousands of miles by migratory birds and was transmitted to hosts in and around nature reserves, which attracted dozens of species of waterfowl.
Conservation groups helped out with the Mongolia outbreak. Although they initially did not believe the dead birds were linked to H5N1 because the number of dead birds was markedly lower than Qinghai Lake. However, the birds were H5N1 positive and the sequences were Qinghai. However these groups then predicted that H5N1 would not spread because the fecal samples from live birds in the area tested negative for H5N1. However, since H5N1 had clearly flown into the region in live birds, the failure to detect H5N1 in any live birds signalled a fatally flawed assay that lacked the sensitivity required for the detection of H5n1 in the healthy birds.
The summer of 2005 signaled the launch of a major propaganda campaign centered on “dead birds don’t fly” and “wild birds as victims”. This campaign included reports published by Promed as well as significant e-mail and internet campaigns. These reports largely depended on the fatally flawed assay of live wild birds to support the two major themes. The reports ignored the sequence data, the failure to detect H5N1 in live birds where there were large numbers of H5N1 positive dead birds, and the (limited) detection of H5N1 by others in healthy wild birds.
The outbreaks in Mongolia and Siberia in the summer were followed by outbreaks in 50 countries in Europe, the Middle East, and Africa. Prior H5N1 outbreaks had not been reported in any of these countries previously, and all outbreaks post-Qinghai Lake were the Qinghai strain.
The following year, the cycle was repeated. H5N1 was again found in Qinghai Province in the spring of 2006, and Qinghai H5N1 was found at a massive wild bird outbreak at Uvs Lake in the summer of 2006 in northern Mongolia and southern Siberia. The H5N1 at Uvs Lake was still clade 2.2, but had a few changes that distinguished the Uvs Lake isolates from earlier clade 2.2.3 isolates.
In the fall of 2006 the Uvs Lake strain was then found in South Korea along a migratory bird flyway that passed through southwestern Korea. The H5N1 was identified in dead poultry as well as feces collected at locations frequented by migratory birds. Although the Uvs Lake strain was not reported in Europe or the Middle East in the fall, it was identified in an outbreak in Kuwait in February, 2007.
The limited detection in the fall or spring of 2007 in Europe led to the pronouncement at the Options VI meeting in Toronto in June, 2007 that H5N1 in wild birds in Europe had been eliminated, based on the false negatives generated by conservation groups collecting fecal samples in Europe, the Middle East, and Africa. However, within minutes of the talk the Czech Republic reported an H5N1 poultry outbreak, which was quickly followed by wild bird outbreaks in the Czech Republic, Germany, and France. These summer outbreaks indicated H5N1 was endemic in wild birds in the region, but was largely undetected. All of these summer outbreaks were due to the Uvs Lake strain of H5N1, but each outbreak had regional differences indicating these outbreaks were due to independent introductions by wild birds.
In the fall, there were outbreaks throughout central and western Europe, and all reported outbreaks were the Uvs Lake strain of H5N1. Multiple sequences from these outbreaks demonstrated near identity, as indicated by a single introductions. These data also supported multiple introductions in outbreaks involving distinct differences, such as the mute swans and Canadian goose in southern England in late 2007 / early 2008. Thus, the overwhelming majority of outbreaks west of China have been due to migratory or resident wild birds. The exception that proves the rule was the outbreak in England in early 2007, which linked that outbreak to the same company with operations in Hungary.
Thus, the current outbreak in South Korea completes a long string of H5N1 outbreaks of clade 2.2 or clade 2.2 precursor sequences, that have been ongoing for more than four years. These outbreaks involve H5N1 that is transported and transmitted by migratory birds.
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