Commentary
Asymptomatic Fujian H5N1 Spread Increases Concerns
Recombinomics Commentary 17:23
June 11, 2008
Following the Road in Sham Shui Po security markets, the Government again in Fanling, Tuen Mun and Ap Lei Chau Li Yan Oi Market swab samples found with the H5N1 avian flu virus and decided comprehensive slaughter of chickens at the retail level.
"We have not found any dead chickens with the virus -- not yet. We have not had any human cases," said Cheng Siu-hing, director of agriculture, fisheries and conservation.
The above translation and comments indicate that the asymptomatic H5N1 in Hong Kong has spread to at least four additional wet markets. This spread highlights the difficulties in controling the spread, since the infected chickens appear healthy. Although Hong Kong has reported H5N1 in wild birds each year, the spread to poultry has not been reported for five years. This spread to poultry extends the number of recent H5N1 events which signal an expansion of the Fujian strain (clade 2.3) of H5N1.
The sequence of the H5N1 from the recent poultry isolates is said to match wild bird isolates from this year. Although Hong Kong has withheld sequence data from H5N1 in wild birds in 2007 and 2008, sequences released from 2006 isolates have been a Fujian sub-clade, 2.3.4. However, the clade 2.3.2 vaccine target is from a wild bird that died in Hong Kong in 2007 and appears to be closely related to the Fujian outbreaks in South Korea, Japan, and southeastern Russian. Those isolates had a clade 2.3.2 HA which mapped to the same location as the 2007 isolate from Hong Kong, providing a link between the 2007 wild bird outbreak in Hong Kong and the outbreaks in 2008 to the north. These outbreaks may also be related to the suspect H5N1 in birds and patients in North Korea.
All of the above represent unusual events. None of the countries to the north have previously reported the Fujian strain of H5N1. The outbreaks in South Korea and Japan are usually associated with wild bird migration into the region from Russia and Mongolia in the fall or early winter. This year the outbreaks were reported in the spring, when birds were migrating into the region from the south.
Moreover, the outbreak in South Korea was the largest reported to date, and the outbreak in Japan was in northern locations which had not previously reported H5N1. The same is true for the outbreak in southeastern Russia, and North Korea has never reported H5N1 infections in birds or patients.
These events raise concerns of a global expansion of the Fujian (clade 2.3) strain of H5N1, which will rival and extend the expansion of the Qinghai strain (clade 2.2) which began in the spring of 2005.
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