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Rapid Spread of H5N1 in Asia Via Migratory Birds
June 8, 2005
The latest OIE report from China implicates migratory birds as the mode of spread for the outbreak in geese in Xinjaing autonomous region, Tacheng district, Tacheng city. The data presented in the report supports infection of the domestic geese by migrating birds. The index farm is a backyard farm with 2,177 geese. 1042 were positive for H5N1 and 460 had died. These numbers suggest a recent virulent lethal infection.
Although the onset date is not given, the earlier OIE report used the same battery of tests. In the May 21 report, the first deaths were on May 5. Since the latest outbreak is also a long distance from the Harbin testing facility, it seems likely that the first dead birds were also found about 16 days prior to the filing of the report, June 8.
16 days ago is when the report on the wild birds was filed and the new site is almost 1000 miles west of the outbreak at Qinghai Lake Nature Reserve. The earlier outbreak led to the closing of all nature reserves in China and shipment of vaccine to Qingahi Province and Xinjiang. Although official press releases indicated the outbreak did not affect domestic poultry in Qinghai, the report did not address infected poutry in Xinjiang. The report also indicated other provinces in China were not at risk.
These comments may be related to the observation that infections were spread by migratory birds heading north and west, and by the time the announcements were made, these birds were exiting China and entering Kazakhstan, Mongolia, and Russia.
These three countries have not reported any H5N1 infections of deaths, although a recent report on the deaths of 400 sheep in Mongolia would have coincided with birds entering Mongolia in late May / early June. H5N1 has not been previous reported to infect sheep, but an Abundant News report indicated the infections in Qinghai caused the deaths of over 8000 birds as well as livestock including sheep.
Usually H5N1 infections in wild birds do not cause symptoms or deaths. The die-off of 1000 birds in Qinghai was called unprecedented. Now there are more deaths almost 1000 miles away. These die-offs on migratory bird flight paths would also support spread via migratory birds and would suggest new infections in the countries bordering Xinjiang.
The rapid spread of the novel H5N1 is cause for concern. Since China has isolated virus from both outbreaks, sequence data would help determine the relationship between the two outbreaks as well as the origin of the H5N1. The initial cases were said to be exclusively bar-headed geese which winter in the plains of northern India. Although recent reports indicated Indian poultry workers were positive for H5N1 antibodies. No virus has been isolated because India, a country with a population of 1 billion, claims to not have the facility for isolating and sequencing H5N1.
Similarly, it is not clear in Kazhakstan or Mongolia has the resources to isolate H5N1, but Russia should be able to isolate and sequence virus. Although there have now been two reports linking H5N1 to migratory birds, directly or indirectly, there seems to be little effort to track the origin or destination of these birds.
Since Qinghai Lake is a resting and nesting site for migrating birds in the East Asia and Central South Asia flyways, H5N1 could be spread in several directions. The monitoring of H5N1 at points of origin and destination seems to be inadequate. New sequences can be expected again in the fall when these birds begin migrating back to their winter nesting sites.
New sequences bring new problems.