Transmission of bird flu to humans slowed after China restricted live poultry sales in cities with the most H7N9 infections, with no new cases in Shanghai since April 13, a week after the financial hub ordered markets to shut.
The CHART OF THE DAY shows a plateauing in the cumulative number of reported cases and fatalities -- now at 129 and 26 -- since mid-April, following market closures in Shanghai, Nanjing and Hangzhou. Infections take a median of six days to cause symptoms, a study in the New England Journal of Medicine found.
“That really does suggest that closing down the live bird markets has reduced the risk of infection,” said Anne Kelso, director of a World Health Organization flu research center in Melbourne who was among international specialists invited to China to advise the government on the crisis last month.
Disease trackers have yet to pinpoint how infections are occurring, with contact with infected poultry identified as the most probable source. Rooting out the viral reservoir will help prevent further transmission and reduce the risk of the virus mutating to become as infectious as seasonal flu -- a scenario that could touch off a deadly pandemic.
“We definitely see the benefits of shutting down live markets, especially in Shanghai and in Jiangsu province,” said Feng Zijian, director of emergency response at the Chinese Center for Disease Control and Prevention, in a telephone interview yesterday. The next step may be to restrict that type of poultry selling nationwide to control the spread, he said.
“It looks like the human infections can be reduced with temporary management of the markets, but this isn’t a long term solution,” said Richard Webby, director of a WHO flu research center at St. Jude Children’s Research Hospital in Memphis. “The biggest question is still where the main reservoir of this virus is,” Webby said, adding that while poultry markets are likely culprits, the specific animal hosts, numbers infected, and mode of transmission between markets need to be understood.
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