H5N1 strain could start wave of bird flu outbreaks
Reuters / Tan Ee Lyn | October 30 2006
Scientists in Hong Kong and the United States have detected a new strain of H5N1 bird flu virus in China and warned it might have started another wave of outbreaks in poultry in Southeast Asia and move deeper into Eurasia.
The strain, called the "Fujian-like virus" because it was first isolated in China's southern Fujian province in March 2005, has increasingly been detected since October 2005 in poultry in six provinces in China, displacing other H5N1 strains.
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 the scientists.
The researchers are from the University of Hong Kong, including virologists Guan Yi and Malik Peiris, and Rob Webster of St Jude Children's Research Hospital in the United States.
"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 in an article published in the U.S.-based Proceedings of the National Academy of Sciences (www.pnas.org).
"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."
The first wave of H5N1 outbreaks occurred in late 2003 and 2004 in many parts of Asia. The second wave started in China's Qinghai Lake in May 2005 and that strain has since been found in parts of Europe, Africa and the Middle East.
The virus has killed more than 150 people since late 2003 and remains largely a disease among birds. But experts fear it could trigger a flu pandemic and kill millions of people if it mutates into a strain that can pass from human to human.
The researchers collected 53,220 fecal samples from chickens, geese and ducks in poultry markets in six Chinese provinces between July 2005 and June 2006. Of these, 1,294 tested positive for H5N1.
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.
"That's pretty conclusive proof that this new variant is predominant," said Gavin Smith, one of the researchers in the Hong Kong team.
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 3 strains of H5N1 -- namely the Yunnan, Guiyang and Fujian-like strains.
The antibodies managed to neutralize the Yunnan and Guiyang strains, but had little or no effect on the Fujian virus.
"The market poultry, many of them don't have antibodies against H5 virus and those that do are not well protected against the Fujian virus, which is why we think the Fujian-like virus has been able to grow because other (strains) have been suppressed," Smith told Reuters in an interview.
"What happens with vaccines is that you basically introduce something that kills off most of the viruses, but there are always going to be some viruses that can escape from it."
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