Chickens to blame for spread of latest deadly bird flu

Chickens started the second wave of H7N9 bird flu that hit China last year, a new study concludes. With a third wave ongoing, pinpointing the source could highlight measures to prevent the disease from turning into a pandemic.

The virus spread from Zhejiang province in Eastern China southward, where it has evolved into at least three local varieties, researchers report online March 11 in Nature.

H7N9 avian influenza first became a concern in spring 2013 when it struck 136 people, killing about 40. The virus nearly disappeared during the summer only to reemerge in the fall. It sickened 318 people and killed more than 100 from October 2013 to September 2014. A third wave began last October. In total, more than 640 people have contracted the virus.

Researchers did not know why the virus bounced back so strongly. So Tommy Tsan-Yuk Lam of the University of Hong Kong and colleagues took samples from live poultry markets in five provinces and from a hospital in Shenzhen. On average, 3 percent of chickens in the markets carried the virus, indicating that the birds were probably the source of the outbreak. Poultry traders probably spread the virus, Lam and colleagues suggest.

If measures such as permanently closing live poultry markets are not implemented, “it will only be a matter of time before poultry movement spreads this virus beyond China,” the researchers write. In addition, H7N9 has picked up genes from other avian influenza viruses that may enable it to infect humans more easily. The combination makes H7N9 “a major candidate to emerge as pandemic strain in humans.”