Study Links Live Animal Markets In China And Human H5N1
By Helen Branswell THE CANADIAN PRESSFeatures New Technology Production
December 20, 2011 – Chinese scientists looked for evidence of the dangerous flu virus in live-bird food markets that six people who came down with the infection in 2008-2009 had reported visiting in the two weeks before they became sick.
December 20, 2011 – Chinese
scientists looked for evidence of the dangerous flu virus in live-bird
food markets that six people who came down with the infection in
2008-2009 had reported visiting in the two weeks before they became
The researchers collected samples from the markets and the individuals' homes, swabbing the bottom of chicken cages, floors in the markets and nearby ditches, then testing the swabs for molecular traces of flu viruses.
A surprisingly large portion of the samples taken were positive for influenza A viruses, the broad family into which H5N1 viruses fall.
Of 69 samples, 31 were positive for influenza A and further testing showed 17 of the 31 were positive for H5N1 virus.
Genetic analysis of the viruses showed they were closely related to the viruses isolated from the human cases, suggesting strongly the markets were the source of their infections.
The study was published in the December issue of the Journal of Virology.
The findings have important public health implications, corresponding author Yuelong Shu warned in a release.
A key concern: that the H5N1 viruses and the H1N1 viruses that caused the 2009 pandemic might simultaneously transmit in these markets, giving the two viruses the chance to re-assort.
One of the ways pandemic viruses emerge is when different flu viruses simultaneously infect a person or an animal such as a pig, giving the viruses a chance to swap genes.
The 2009 H1N1 virus is a particular concern in this regard because it has an internal gene, known as the M gene, that seems easily able to move into new gene constellations. Studies of this M gene suggest it makes flu viruses more transmissible in guinea pigs, which are considered a good model for what happens with flu viruses in humans.
"Enhanced infection control measures are warranted in these markets, not only to reduce human H5N1 infection, but also to minimize the likelihood of co-infection with H5N1 and 2009 H1N1 viruses,'' the researchers wrote in the article.
"The sporadic cases of human H5N1 highly pathogenic avian influenza infection, the H5N1 outbreaks in birds, and the simultaneous circulation of the 2009 H1N1 pandemic virus raise concern that a deadly reassortment virus may emerge.''
Concern has long focused on the crowded live animal markets of Asia as a potential point of transmission between animal viruses and people. For instance, severe acute respiratory syndrome or SARS was caused by a coronavirus that probably passed to humans from civet cats and raccoon dogs sold in the so-called wet markets.
In 1997 in Hong Kong, when H5N1 viruses first began infecting humans, director of health Dr. Margaret Chan –now director general of the World Health Organization – ordered the destruction of all live chickens in the city in an effort to try to eliminate the threat.
There were no more cases at the time, but the virus was clearly spreading among birds elsewhere and in 2003 it roared back with a vengeance. Over the next several years, millions of poultry were culled in Southeast Asia and beyond.
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