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Bird Flu in Tacheng Highly Pathogenic for Geese and Chickens
June 10, 2005
>> On June 1, geese death was reported at a backyard farm 32 kilometers from the city proper of Tacheng. Three days later, the national bird flu reference laboratory confirmed the death to be caused by a deadly H5N1 strain of the bird flu virus. The number of geese infected totaled 1,042, 460 of which have died, Chen said.
The governments of Tacheng prefecture and Tacheng city have ordered all the poultry markets in Tacheng City to be closed down and had 17,014 birds slaughtered in the affected area, most of them chickens and geese. Roads to the affected area have been blocked and traffic has been closed. <<
The above dates, if accurate, would indicate the H5N1 bird flu in Tacheng is very pathogenic to chickens. In the OIE report dated June 8, the H5N1 was said to be highly pathogenic based on two assays. One assay sequences the HA cleavage site while the other involves injecting new virus into test chickens and observing the chickens for 10 days for signs of illness or death. The testing was done at the Harbin facility which is on the eastern side of China while Tacheng is a border town within a few miles of the west border share with Kazakhstan.
To perform the 10 day test the samples would have to be collected in Tacheng, shipped to Harbin. Next the virus would be isolated from the bird samples and then grown in chicken eggs. Fluid from the eggs would then be tested to get a viral titer and then diluted to the appropriate concentration and injected into eight chickens. Those chickens would then be observed for 10 days.
Since the first reported goose death was June 1 based on the above report (the date of onset was left blank in the original report submitted to OIE), it would take several days to prepare the virus for the biological assay. Since the report was publicly available on June 8, the determination of lethality in chickens was made in less than the 10 day observation period (the report indicates it was completed June 7), indicating the H5N1 killed the chickens very quickly.
The geese also died quickly since almost half of the flock was infected and half of the infected birds had already died. The closing of poultry markets and the additional culling also suggests the H5N1 is quite lethal. The June 8 report indicated 13,457 birds had been culled, so an additional 3,557 birds have been culled.
H5N1 is usually not lethal in geese. China has now filed two OIE reports within the past 19 days detailing large die offs of migratory and domestic geese. These changes in H5N1 point to increased instability, which is driven by recombination between H5N1 genomes.
The gene pool is rapidly increasing in size and diversity, increasing the likelihood of a flu pandemic in the near term.