Long Range H5N1Transport and Transmission by Migratory Birds
Recombinomics Commentary 20:41
January 24, 2008
"We know that some wild birds have probably moved short distances carrying viruses and then they died, but we have not been able to identify carriage of H5N1 across large scale spatial distances and then resulting in spread to other birds and mortality in poultry flocks," Newman told Reuters.
He said fecal tests on some 350,000 healthy birds worldwide had to date only yielded "a few" positive H5N1 results.
Furthermore, in instances and places where wild birds were found with the disease, there were no concurrent outbreaks of the virus in poultry.
"So we don't have at this point in time a wildlife reservoir for H5N1 ... so they can't be a main spreader of the disease," Newman said.
The above comments on negative data on testing of fecal samples from live wild birds are remarkable. The fatally flawed approach was used over two years ago in Mongolia, when wild bird deaths were reported at the remote Erhel Lake. The failure to detect H5N1 in the live birds at the lake left little doubt that the approach was flawed. Now two and half years and 350,000 tests later, these data are used to “prove” that migratory birds are not the major transport and transmission vehicle of H5N1 in the 50 countries reporting H5N1 since the outbreaks in the spring and summer of 2005.
The role of the migratory birds was really decided in the summer of 2005, when false negatives were being generated at Erhel Lake. In the spring of 2005, H5N1 was found in long range migratory birds at Qinghai Lake in central China. The H5N1 reported was a novel variant, which had unique genetic features, including the acquisition of a “human” change in one of the enzymes used to copy the viral genome. This change PB2 E627K was a concern because it had never been reported in H5N1 from a bird, and the change allowed the virus to replicate more rapidly at 33 C, the temperature of a human nose or throat in the winter. Since the body temperature of a bird is 41 C, the “human” change slowed down the replication of the virus in birds. However, the H5N1 could still be quite lethal, since 5,000-10,000 wild birds died at Qinghai Lake.
The high number of deaths raised the possibility that the strain would “burn out” at the lake. However, Qinghai Lake is the largest lake in China and attracts a large number of species of birds, so when H5N1 was reported at Chany Lake in southern Siberia, which was 2,000 miles from Qinghai Lake, the role of long range migratory birds was becoming clearer. Prior to the summer outbreak at Chany Lake, Russia had never reported highly pathogenic H5N1, so the wild birds were the prime suspect.
H5N1 was isolated from a healthy grebe, and the sequence was the Qinghai strain. Thus, at that point there was little doubt about the role of wild birds in the transport to Chany Lake, and the transmission to nearby poultry in Russia and Kazakhstan.
Any doubt that remained was removed by a similar, almost simultaneous outbreak at Erhel Lake in Mongolia. Like Russia and Kazakhstan, Mongolia had also never reported H5N1 prior to the summer of 2005. When wild birds began to die at the remote lake, conservation groups joined in the study. These groups initially said that the bird deaths couldn’t be due to H5N1 because there were fewer than 100 dead birds. When initial results of H5 came back, they again maintained that the H5 would not be from H5N1 because there were not enough dead birds. Then when the H5 was determined to be from Qinghai H5N1, the conservation groups said H5N1would not pose a problem because the live birds at the lake tested negative for H5N1.
At that point it was clear that the Qinghai H5N1 had the potential of causing greater problems because it was killing a small number of birds. Thus, it was more likely that live birds would transport the H5N1. The failure to detect the H5N1 in live birds in an area where dead birds were H5N1 positive, signaled a fatally flawed assay.
In Siberia, the number of reports of H5N1 in wild birds continued to grow during the summer, signaling further spread in the fall when the wild birds would head south. The potential for spread was great, because Chany Lake and other small lakes in southern Siberia or northern Kazakhstan hosted a large number of waterfowl in the summer, and these locations were in intersecting flyways, so the H5N1 could fly off in several directions. The flyways predicted that the H5N1 would move into Europe, the Middle East, and Africa in the ensuing months, which happened.
Although none of the countries west of China had previously reported H5N1, the reports began in the fall of 2005. H5N1 was found in mute swans near the Volga Delta, at the northern end of the Caspian Sea. That was followed by H5N1 in mute swans in the Danube Delta on the western shores of the Black Sea, which was followed by H5N1 in wild birds in the Crimea Peninsula, which juts out into the Black Sea, which was followed by H5N1 in a healthy teal in the Nile Delta at the end of 2005.
Although H5N1 was reported in wild waterfowl at the above locations, countries in the EU denied H5N1 infections, as did countries in the Middle East and Africa through the end of 2005. However, after H5N1 caused human fatalities in eastern Turkey at the beginning of 2006, H5N1 was widely reported at all of the above locations in February and March of 2006. Moreover, all H5N1 reported was the Qinghai strain of H5N1, although there were regional differences in sequences, reflecting independent introductions by wild birds.
In the summer of 2006, the cycle repeated. This time there was a massive wild bird H5N1 outbreak at the largest lake in Mongolia, Uva Lake near the Russia / Mongolia border. Most countries again denied H5N1 infections in the fall of 2006 and early 2007, but in the summer of 2007, H5N1 was found in multiple wild bird outbreaks in Germany, the Czech Republic, and France. In all cases the H5N1 was the Uva Lake strain, which was a variant of the Qinghai strain.
The outbreaks in the summer in Europe signaled more activity in the fall and winter, which happened, and all reports in Europe have been the Uva Lake strain.
Thus, the role of wild birds in the transport and transmission of H5N1 in Europe, the Middle East, and Africa is quite clear, fatally flawed live wild bird screening notwithstanding.
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