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H5N1 Wild Bird Flu in Qinghai China
May 1, 2006
A wild goose found dead in northwestern China has tested positive for the deadly H5N1 strain of bird flu, the government said Monday. The Qinghai region is a stopping point for migrating birds.
The above report of H5N1 in a wild goose in Qinghai Province in China completes a one year cycle of the H5N1 Qinghai strain. On May 9, 2005 189 bar-headed geese were reported to have died at the Qinghai Lake nature reserve. Although H5N1 involvement was initially denied, the May 21 OIE report described 519 dead waterfowl at the lake. Most were bar headed geese and H5N1 had been found in the geese as well as black and brown headed gulls. H5N1 in dead waterfowl was unexpected because most waterfowl are resistant in to H5N1 and most avian influenza in waterfowl are low pathogenic avian influenza. The H5N1 at Qinghai Lake was highly pathogenic and killed experimental chickens within 20 hours.
H5N1 in bar-headed geese was a concern because they are long range migratory birds that can travel 1000 miles in a day, thereby spreading H5N1 far and wild. Moreover the Qinghai nature reserve was at a the intersection of several migratory bird pathways and a year ago the Asian version of H5N1 had not been reported north or west of China.
Several weeks later there were H5N1 outbreaks at farms in western Xinjiang province, indicating that the H5N1 did not die out at Qinghai Lake, but instead was migrating, as expected to the Chany Lake reserve at Novosibirsk in southern Siberia. This nature reserve was at the intersection of several migratory bird pathways that connected southern Siberia to Europe, the Middle East, Africa, and North America.
In early July sequence data from the H5N1 Qinghai strain was released. Although the sequences were readily distinguished from the Asian strain of H5N1 in China, many of the characteristic features such as the poly-basic HA cleavage site, the 20 amino acid NA deletion, and the 5 amino acid NS deletion were present. The strain was most closely related to H5N1 from eastern China, but sequences from Europe were also present, including European swine.
The Qinghai strain also had PB2 E627K. This polymorphism was present in all H1, H2, and H3 isolates from humans, but had not previously been reported for an H5N1 isolate from a bird. H5N1 from humans or cats had E627K, and the presence of E627K in H5N1 from mammals was linked to a poor prognosis. E627K was also found in a fatal H7N7 case in the Netherlands in 2003 and lab experiments showed that E6276K increased virulence in mice. The polymorphism also was linked to enhanced polymerase activity at lower temperatures, consistent with rapid replication in mammals. E627K was found in all 16 Qinghai Lake isolates from wild birds.
In July H5N1 was reported at Chany Lake in Russia as well as Kazakhstan and Mongolia. Sequence analysis indicated the H5N1 was the Qinghai strain and the isolates also had E627K. These data left little doubt that H5N1 had become established in the wild bird population and would continue to spread worldwide.
After extensive spread in southern Siberia in the summer, H5N1 then migrated into Europe in the fall of 2005. Initial reports were of H5N1 in the Volga Delta in Astrakahn, the Danube Delta in Romania, as well as outbreaks in western Turkey and Croatia. The OIE Mission report from Russia indicates H5N1 was widespread and had been detected in over dozen wild bird species shot down by hunters. These data further supported the worldwide spread of H5N1, which prior to last July had only been reported in China and countries to the south and east.
H5N1 was subsequently detected throughout Europe, the Middle East, and Africa. Although many countries in these regions have failed to detect or report H5N1, there is little doubt that H5N1 spread throughout the regions in the Fall and Winter and is now beginning to return north, as evidenced by the new report in Qinghai Province.