New bird flu strain takes hold
Scientists in Hong Kong and the United States have
detected a new strain of H5N1 bird flu virus in China that is overtaking other
The strain has increasingly been detected since October 2005 in poultry in
six provinces in China, displacing other H5N1 strains.
The researchers collected 53,220 fecal samples from poultry markets across
China between July 2005 and June 2006. Of these, 1,294 tested positive for
But genetic sequencing of viruses collected from October 2005 onwards
showed the Fujian strain was clearly becoming predominant over other H5N1
strains. Between April and June this year, 103 out of 108 H5N1-positive samples
were of the Fujian type.
The strain might also have become resistant to vaccines, which China began
using on a large scale from September 2005 to protect poultry from H5N1, said
To test how well vaccinated poultry could stand up to various strains of
H5N1, the researchers collected 1,113 blood samples from chickens from November
2005 to April 2006.
Only 180 samples, or 16 percent, tested positive for H5N1 antibodies. They
were exposed to the Yunnan, Guiyang and Fujian-like strains.
The antibodies managed to neutralise the Yunnan and Guiyang strains, but
had little or no effect on the Fujian virus.
"The predominance of this Fujian-like virus appears to be responsible for
the increased prevalence of H5N1 in poultry since October 2005 and recent human
infection cases in China," they said.
"It has already caused poultry outbreaks in Laos, Malaysia and Thailand,
and human disease in Thailand. It is likely that this variant has already
initiated a third wave of transmission throughout Southeast Asia and may spread
further in Eurasia."
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