Silent spread of bird flu raises pandemic fears

From ABC News in Science, 12 March 2015:

A deadly strain of bird flu known to infect humans is spreading rapidly and silently through chicken populations across China.

The findings, published today in Nature, raise fears of a bird flu pandemic, as the sheer size of this disease reservoir increases the likelihood of a mutation that would enable human-to-human transmission.

The H7N9 strain of avian influenza first reared its head in humans in early 2013 in eastern China, prompting a rapid shut-down of live bird markets.

It then re-emerged in late 2013 in a second wave that led to 318 human cases and over a hundred deaths.

Taking swabs from birds at live poultry markets in five different western Chinese provinces, researchers have now found evidence that the H7N9 virus is moving across China and gaining genetic diversity as it does so.

“We’ve shown is that even though they [Chinese authorities] did a very good intervention to stop the virus contacting humans by closing live bird markets, in fact this virus is deep-seated in the chicken population all over the country,” says co-author Professor Edward Holmes, infectious diseases specialist at the University of Sydney.

This makes it all but inevitable that the virus will escape Chinese borders and spread elsewhere in the world, just as the H5N1 and H9N2 influenza viruses have done previously.

As chickens show no outward signs of being infected by the H7N9 virus, it is difficult to monitor and control.

Taken together with the sheer numbers of likely infections in chickens, this makes it ever more likely that the virus will spread to humans, Holmes says.

“The time bomb — which may never go off — is human-to-human transmission,” he says. Read more.

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