Uva Lake H5N1 in Europe
Recombinomics Commentary
November 30, 2007
It says that there are two main theories about how the disease was introduced to the UK - either via contamination from people from a country with an undisclosed infection in their domestic flocks, or infected wild birds.
There is currently no evidence to support either theory.
"As there are no epidemiological links with domestic poultry in central Europe, the molecular genetic results suggest that wild birds may have introduced the virus into Suffolk from Europe," the report said.
Although there is no direct epidemiological evidence between the domestic birds and H5N1 isolated from wild birds in the area, there are direct links to wild birds. The domestic poultry was free range and adjacent to a large artificial lake with wild birds, which could also access the feed on the farm.
Detection of H5N1 in live wild birds in Europe is rare, and these failures can be linked to many factors including a low level of H5N1 in live birds, limited testing, and procedures linked to collection, transport, and storage.
The genetic linkage however, is strong. The sequences of the three isolates from Germany have been released for HA and NA. All six of the sequences are closely related to sequences from Krasnodar this fall, and signal widespread H5N1 in Europe. These sequences trace back to the wild bird outbreak at Uva Lake in Mongolia in the summer of 2006. Moreover, the recent H5N1 reports from Germany, France, and the Czech Republic on infections over the summer indicate those outbreaks also involved the same subclade, as did an earlier outbreak in Kuwait. The identity between these sequences is in the 99.2%-99.8% range, which signals independent introductions by wild birds infected with H5N1 linking back to Uva Lake. These sequences are distinct from earlier H5N1 infections and all recent public NA sequences have G743A.
The detection failures in Europe are similar to earlier reports which failed to detect H5N1 in live wild birds when dead or dying wild birds in Europe were common. These deaths were linked to harsh winter conditions in early 2006, which may have led to an increase in bird deaths link to host specific stress that could be linked to a variety of external factors including other infections, food shortage, or cold temperature. The vast majority of Qinghai PB2 sequences have E627K, which leads to increased viral replication at colder temperatures.
Thus, expectations of large numbers of dead or dying wild birds are not based on prior outbreaks, and such expectations do not exclude wild birds. The linkage to wild birds has been strong. All H5N1 west of China has been the Qinghai strain, and the initial outbreaks in 2005 were linked to waterfowl at Qinghai Lake, Erhel Lake, Chany Lake, Volga Delta, Danube Delta, Crimea Peninsula, and Nile Delta, corresponding to migration paths, including overlapping flyways.
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