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China's Bird Flu Might Someday Spread More Easily

For now, however, the virus doesn't transfer well from human to human, experts say


Bresee noted that, so far, the H7N9 virus does not spread easily from human to human, but it is still concerning.

"It can cause severe disease and deaths in humans. The one thing that gives us comfort so far is that it doesn't seem to be able to spread efficiently between humans and that's what allows a flu virus to develop into a pandemic virus," he said.

Not only is the CDC watching this virus, Bresee said: "The whole world is watching."

Within the United States, the CDC has told state health departments what to look for and how to test for H7N9, Bresee said.

The agency is studying the virus, watching for mutations and trying to understand what medicines work against it. Moreover, the CDC is developing a vaccine against the H7N9 flu, he said.

"When the virus was first discovered and we got our samples here at CDC, we started vaccine development right away," Bresee said. "The U.S. government is developing and testing vaccines just in case we need to use them at some point."

The Chinese researchers investigated the virus from a variety of sources.

Chen's team identified dozens of H7N9 strains from more than 10,000 samples taken from poultry markets, poultry farms, wild bird habitats and slaughterhouses across China.

The researchers looked at the genetic makeup of these strains, comparing them with the genetic makeup of five of the strains found in people.

All strains of the virus could go to airway receptors in humans, and some could be transmitted to birds as well.

All of the H7N9 strains from birds easily went to chickens, ducks and mice without causing any disease. The human strains, however, caused mice to lose up to 30 percent of their body weight, the researchers said.

In addition, one of the human strains easily went from ferret to ferret.

Whether the virus will mutate, making it easier to transmit from human to human, is not assured, Siegel said.

"That's probably better left to science fiction, because mutations also occur that make something more benign," he said.

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